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Duraforce Re-jetting Instructions Part 2

Posted by FordTech ok (My Page) on
Wed, Jul 13, 05 at 22:33

Thanks to Tom_P_PA for the first 100 post thread, this to be a continuation of which I repost the instructions in this first post. Only 100 posts are allowed per Subject
"quote"
Also, the mikuni on the suzuki 2 stroke part number is 81-1030 which is matches the Duraforce "37.5" jet and is a #40.

1) Get a NEW main jet and pilot jet. Part numbers are 98-1357 and 98-7041. Also, get the paper gaskets (1 for the carb body and 2 for the heat shield), get a fuel line and in line fuel filter.

2) Note that the main jet 98-1357 is called a "77.5" jet. The "77.5" jet is the jet orifice size in one-thousands of a centimeter. The closest drill bit size is a #68 wire gauge drill bit whose diameter is 0.031 inch (and it fits into the orifice, and #67 does not).

3) Note that the pilot jet 98-7041 is called a "37.5" jet. Again, the "37.5" is the jet orifice size in one-thousands of a centimeter. The closest drill bit size is a #79 wire gauge drill bit whose diameter is 0.0145 inch (and it fits into the orifice, and #78 does not).

4) Get a wire gauge drill set (from #80 to #60), or better still, get drill sizes #66 (0.033 inch) and/or #67 (0.032 inch) for the main jet and #78 (0.0160 inch) for the pilot jet. You will need a hand chuck to mount these tiny drills. Do not use power tools. This results in an approximately 10% increase in the orifices for both jets. 10% is all that is needed.

5) Carefully hand drill the jets, apply gentle pressure. Note that the pilot jet center hole is to be drilled ONLY. Do not drill through the body of the jet, drill out only the 37.5 orifice. Use the #78 drill to oversize the pilot jet orifice (it is the first oversize). To oversize the main jet, you can use a #67 drill (0.032 inch), go back and forth and ream out unit the #66 drill (0.033 inch) just fits, or you can use a #66 (0.033 inch) drill - but be careful to not oversize the orifice.

6) Carefully drain all of the gas, remove and disassemble your carb adn replace the existing jets with the new modified (oversize) jets. Not the pilot jet is on the side of the carb and is covered up with a sticker. Take the sticker off to get access to the pilot jet.

7) Be real gentle when putting the new jets in, do not apply excessive turning force...a new carb will set you back $100.

8) Reassemble the carb and adjust the speed control vane one click slower. The engine speed may run fast after these mods.

9) Reinstall the carb with a new gas line and in-line fuel filter. Note, its a real good idea to install an in-line fuel filter. The carb jets are small and can plug up easily.

10) Gas and go.

Your mower will consume a bit more gas but will not surge any more because your mower's mixture will be a little richer. However, the engine will be better lubed and cooled as a result. This cures surging and makes the mower runs like mowers of 10 years ago.


Follow-Up Postings:

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RE: Duraforce Re-jetting Instructions Part 2

Thanks for continuing the posting..appears it is continuing to give people lots of value.

I am so excited about my mower now. It cured a 2 year head ache for me.

I am considering another tear down and going up one more on the bit. I have a similar situation as Hawkeye described (very slight surge once in awhile). I did one up on the bits so far. I guess the worse case is that it runs too rich and I need to purchase new bits and start over.

What is the recommendation...do both jets..or just the main?

Could the Duraforce maybe, just maybe, make it into the LB Hall of Fame??


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RE: Duraforce Re-jetting Instructions Part 2

Blaise--

I haven't found a good used DuraForce carb on eBay yet. When I do, I'll bid on it and, if I win, I'll re-jet the used one instead of the one on the mower in case I do something wrong.

It sounds like re-jetting really makes a difference in performance. I'm looking forward to doing it eventually.


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RE: Duraforce Re-jetting Instructions Part 2

"This was about the third or fourth time I've taken carbs off of DF's - I'm getting better but they are a pain in the butt! Have patience."

They are a pain. I found it tedious on reassembly of the carb and trying to keep all the parts together and get the spring into place. My heat shield remained "stuck in place" on the engine when the carb was removed...However, I made the mistake of bumping it off, and had that to deal with another loose piece on reassembly too.

I also made the primer hose mistake Tom mentioned about and could not reinstall it onto the carb and through the white plastic hose holder fig-a-mag-ig. I tried and got pissed off at it and just removed it again.



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RE: Duraforce Re-jetting Instructions Part 2

Today I cleaned the carb on project 22261.
Someone had already done the suzuki mikuni low speed jet swap and drilled the main 2 sizes larger.
The mower is a 2001 model and ended up in the junk yard last fall.I didn't notice any carbon build up or deposits in the rings.Plug looked perfect.
Since the engine is still nice and tight maby there is some hope for longevity in a jetted Duraforce.


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RE: Duraforce Re-jetting Instructions Part 2

There is a case for at leaset one new heat shield gasket...
p/n 94-5795. Specifically the one between the heat shield and the engine. New gaskets have semi-circular holes that, when the carb screws are threaded into, grip the screws and hold the air box-gasket-carb-gasket-heat shield-gasket assembly together enough to replace it with out parts flying around every where. It holds the whole thing together as if you had nuts on the end of the screws.

AJT


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RE: Duraforce Re-jetting Instructions Part 2

I find it helps to remove the 3 screws around the engine shroud and move it out of the way. Gives a little more room to work and better visibility of the area.


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RE: Duraforce Re-jetting Instructions Part 2

I finally had the time to re-jet my 10550 yesterday. It took a little longer to do the job than what others posted because of a few extra steps I needed to do. After performing the over size ream of my main jet I promptly dropped the jet on the floor which then rolled under my work table and disappeared into the cold air return duct :o 45 minutes later after tearing open the duct from the basement retrieving said jet and resealing the duct, I was ready to re-jet my mower. Murphy's Law I guess!

Like I had said before I was conservative on my reaming and only oversized each jet by one bit size; although, I did follow the suggestion of my local mower shop L-B guru and upsized both pilot and main jets at the same time. The stock pilot jet allowed a bit number #79 to fit and I reamed it with #78, and the #77 would not fit. The main jet came out a little larger than one bit size because the bit I used bound up as I fed it into the orifice and I spent extra time reaming to smooth the jet orifice wall after it went through. In this case a stock main jet allowed a bit # 69 to fit and I reamed it with #68 and afterward #67 fit but #66 would not. I removed the engine shroud and rear drive belt cover to improve access and was able to keep the air cleaner housing and carburetor and throttle cable together which avoided some messing with that part of the control assembly. I didn't bother adjusting the governor.

The results were noticeable. It fired right up with 2 primes and choke. The temperature was in the upper 80s and humid and the motor smoked at first (expected) and seemed to surge at slow speed (unexpected). As the motor warmed up the smoke cleared and settled into a nice intermittent burble sitting on the drive with no load at full throttle and at slow throttle the surging was gone. It has been very dry here so there isn't much to mow, but there was a small section of lawn that had some turf tall enough to mow and the re-jetted motor ran great with good power and no burble under load.

I suspect that I could have went larger to where a # 77 bit fit the pilot jet orifice and a # 66 bit fit the main jet orifice resulting in jetting closer to perfect because with this one bit size larger re-jet I noticed a slight lean spot at a middle throttle setting between the pilot and main circuits. Also, I suspect it likely will be on the lean side overall by late October when the temperature is below 60F. However, the jetting is pretty close to perfect so I'm leaving it for now to see how it goes. Except for added step of having to tear up the cold air return duct on my house the re-jetting job was easy and it gave the desired results.


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RE: Duraforce Re-jetting Instructions Part 2

Gardyn; Did you reuse the gaskets?


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RE: Duraforce Re-jetting Instructions Part 2

The intake gaskets and heat shield came apart with no problems as did the float bowl. There was no sealer on them from the factory so I didn't have to use the replacements I bought.

I wasn't expecting any problems as I only have about 15 hours on my mower so they weren't baked on and brittle, but I did buy a set just in case.

I mowed the tall grass in my ditch today with the re-jetted Boy and it ran very It is very close to perfect and I may try increasing the pilot jet orifice to a #77 or even a # 76 bit size. I'm thinking the pilot may be an easier way to fine tune it and if it is a little rich at idle speed, so what I'm a full throtle mower kind of guy anyway.


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RE: Duraforce Re-jetting Instructions Part 2

For that part throttle flat spot best bet is to go up another size on the main.
Then do the idle jet fine tuning. 2 strokes make best power with a rich A/F ratio.


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RE: Duraforce Re-jetting Instructions Part 2

Reposting this message from the first thread, since it was near the end of that one. I used one of my mowers again already. What a pleasure to use now!

I also wanted to add another tip: I used a micrometer to make sure I was using the correct bit. The bits are so small, and I wanted to be sure I used the right one. The micrometer confirmed the size for me.

My #68 bit had to be turned in on both, and the #67 just took out one tiny shaving. I stopped there. Both engines had just the slightest hint of a tiny surge afterwards, but only something I would notice and only once it a while. That tells me I didn't over-do it. Most of the time, they had the perfect, smooth hum and burble sound.
Here are some other observations:

1. This was about the third or fourth time I've taken carbs off of DF's - I'm getting better but they are a pain in the butt! Have patience.

2. I actually noticed less smoke and a better smell, if you can believe that.

3. They just sound, smell, and run like a Lawn-Boy should. I'd even bet that they burn cleaner now.

4. I'm tempted to go up one more size. I feel confident it would not be too much for the engine, as others here have noted.

Thanks to everyone who's commented on this post. A year ago, I was scared to try this. Now I know process is easy (took me less than an hour to do 2 engines). It makes the DF run the way it was meant to run. What a difference 1/1000th of an inch makes!


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RE: Duraforce Re-jetting Instructions Part 2

THS_Hawkeye, I used a #66 bit on mine, it runs perfect! It has the burble, settling into a nice steady hum when I hit the heavy stuff, and gives a nice, small puff of smoke when it first hits the governor. I did not touch the pilot jet, I like the wy it sounds when idling way too much for that! It has a nice "pop" to it at idle. I also no longer have to prime it...it will start first pull with just the choke.


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RE: Duraforce Re-jetting Instructions Part 2

Well, I now have the tools needed to do the job, but I was astounded at how thin and fragile the #78 is. I probably will just do the main with the #67 (or #66, as per snuffy). I would probably break the little bit off in the pilot jet.


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RE: Duraforce Re-jetting Instructions Part 2

I didn't do the pilot jet either for the very reason Saxman mentions. Only the main and I went to the #66 bit. I mowed again yesterday for only the second time since re-jetting and I'm still shocked and amazed by the improvements. Wow, sunny, 94F with soaking humidity and I'm enjoying myself. =;^)

The personal pace is now much much smoother and disengages more readily.

I did prime and choke when I started it "cold" yesterday and it only required one anemic pull on the rope to start. Previously, before rejetting it was typically 2-3 pulls. Hot starting was very easy at any engine speed.

Cheers,
jarrall


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RE: Duraforce Re-jetting Instructions Part 2

Saxman...don't worry about the small bit. Just choke it up into the pin vise so only a small portion is exposed outside the vise. When drilling, it does not have to go in very far at all before it opens up into the large center orifice at which point your are done. The tiny orifice that needs drilling does not go the entire length of the jet. Just keep it straight and be patient. It actually feels like nothing is happening at all, but all of a sudden, it pops through, and viola, your are done. Actually, I think I am going to re-bore mine a second time and go up one more on both the pilot and main. After hearing how the 22261 runs, I want the others to run the same.

I am also amazed. The rejetted 10550 and 10323 require one prime pump and one to two pulls. The 22261 has started in two pulls with no prime.


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RE: Duraforce Re-jetting Instructions Part 2

Isn't it sweet when a 2 stroke motor is jetted right. Damn politicians; can't write law to save their life, what makes them think they can jet a motor correctly.

I talked to my brother who bought a 10552 this year and he said now that his mower is broke in it is a nasty surger. I orderd up a set of jets and we'll install them over a few brews. I think I will try a reaming his jets with a #77 bit on the pilot and a #66 bit on the main right from the start because his Boy seems to surge more than my 10550 ever did.
We'll be sure to check for the air leak on the intake track. Now that I'll soon have experiece with re-jetting a lean running non surger (mine) and a full on Durasurge (his) I'll be able to add detail to the knowledge base here. I think I'll be able to update you all in about a week. Stay tuned.

I'm sure that fans of whatever 4 cycle motor is on their mower that was bought in the last few years are likely running a touch lean as well and might benefit from a little "tuning" too. A mini tea party we've got goning here!!!


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RE: Duraforce Re-jetting Instructions Part 2

Gardn_dlyte--

You brought up a good point. I've heard that Phase II compliant flatheads are leaned out to the max. If that's true, they definitely could benefit from some tuning.


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RE: Duraforce Re-jetting Instructions Part 2

I suspect my Honda GCV 160 cc runs a little lean, too. I think we're onto something here! I loved the old days when you just made fine adjustments to the needle valve every so often. For example, if I needed more power for some heavy cutting, I would go maybe 1/8th turn rich - not enough to smoke, but it would keep the 3.5 HP B&S from stalling. These new mowers are set up way lean, and slightest bit of dirt or varnish build-up anywhere in the carb takes then too lean. They still run, just with less power.


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RE: Duraforce Re-jetting Instructions Part 2

Saxman, we are all looking forward to your comments after you rejet. You held out the longest and was a proponent of vane adjusting rather than rejetting. Let us know.


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RE: Duraforce Re-jetting Instructions Part 2

Finally I mowed with the re-jetted LB 10247 for about 3 hours. It was great! The back half of the yard was very dry and the front was long where it has been watered. Prime once when its cold and it starts first pull.

Set the governor down to 3600 rpm at full throttle. It used significantly less fuel re-jetted at 3400-3600 rpm vs. running at 3900 rpm before re-jetting. It quit smoking after 5-10 minutes. There is more exhaust smell, closer to an F or D exhaust. It defiantly ran cooler. I used it on the back part of our yard which was dry, light load, no surging. I used it on the front yard w/ bagger. Great to here it hunker down in the thick stuff. It was cool mowing with the lower pitch sound in the 3400-3600 rpm range and not having to wear ear protection. Was so much fun I didn't even check the mower at idle speed. Still may order the pilot jet.

It does have the intermitted exhaust pop/ping (or p p p p p p ), especially when not under a load. It sometimes gets a slight surge when turning at the end of the row. If it wasnt for the exhaust ping it would sound close to an F motor. Is the exhaust ping normal on a DF? Is that a symptom of running too rich? The spark plug looks good.

Once again, thanks to all the contributors on this forum Like someone else mentioned, I remember reading about re-jetting last year. Thought it was way over my head. Id never taken a carburetor apart. Had just purchased the 10427 and it surged. Took it back to a LB mechanic, he fixed the surge by setting it to run full throttle at 3900-4000 rpms. I knew it was too loud and thought the LB D & F motors sounded better. After many forum reads and successfully working on a couple of dump finds, thought Id give re-jetting a try. Before re-jetting I was about to sell the 10247 and use my dump finds and the Honda/LB. Its much better now with the deep throaty sound of a 2 cyl.

Ken


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RE: Duraforce Re-jetting Instructions Part 2

"Is the exhaust ping normal on a DF?"
Yeah, because the DF is the only 2-cycle LB with the muffler above deck. It will never sound like an F for that reason, and the little pops when the load is gone are more audible. It also sounds like maybe you could have used the #66 drill instead of the #67, or maybe you need to do the pilot jet and see how it affects running before reaming the main jet any more.


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RE: Duraforce Re-jetting Instructions Part 2

Thanks Saxman1, I'm the one that dropped all those bits. The best I could tell I only reamed it out one size but I may have went 1 - 3 sizes. It would be nice to known for sure. May buy a main jet, figure the exact size of the bits and repeat this again. I think Ill try getting the next size pilot jet first. Really like the way it sounds now. Ken


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RE: Duraforce Re-jetting Instructions Part 2

Definatelty normal to hear a pop sound out of the exhaust as it idles or burbles under no to little load. I may be a bit out of school on this but I think that when L-B squeezed the last bump in power out of the engine design, they needed to optimize the exhaust volume on the DF in a way that the under deck exhaust wouldn't allow. Tuning of the exhaust is even more critical on a 2 stroke than on a 4 stroke motor as it is crutual in not allowing the fresh charge to follow the burnt charge out of the exhaust port before the piston skirt closes the port opening. Anyhow, I have also noticed the crisp pop in the exhaust which sort of reminds me of the sound that a highly tuned two stroke race engine makes. So, the DF doens't remind me of my F motor L-B mower, but it does bring back fond memories of my racing dirt bikes.

I guess it should be no wonder why I like to mow full thottle with the Easy Pace maxed out.....I think I have to practice some hole shots with my 10550 to be sure I'm leading coming into the first turn ;)


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RE: Duraforce Re-jetting Instructions Part 2

Has anyone investigated the possibility of putting an F lower plate and muffler on the Duraforce engine? I dont know what all would be required but I have thought how interesting that might be, and wondered how much power loss might be realized from that configuration.


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RE: Duraforce Re-jetting Instructions Part 2

I like that idea, FordTech! That would bring the new Toro-Boys back to the good ole OMC days!


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RE: Duraforce Re-jetting Instructions Part 2

How about fitting the DuraForce with a D-600 bottom plate and aluminum muffler? Does anyone think that this can be done? Those D-600 mufflers are pretty big, so it seems to me that one would work with the DF.


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RE: Duraforce Re-jetting Instructions Part 2

" they needed to optimize the exhaust volume on the DF in a way that the under deck exhaust wouldn't allow. "

I have heard this before but looking at the DuraForce muffler and remembering some of the "F" series BIG round mufflers and the D600 mentioned, I think they could have put the muffler under but I think it had to do with some pinhead's concern about damage to grass or fire hazard is why it was put above deck.

Walt Conner


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RE: Duraforce Re-jetting Instructions Part 2

I thought it was above deck simply to enable EPA testing of the exhaust safely.


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RE: Duraforce Re-jetting Instructions Part 2

Walt,

The volume is only part of the consideration for a two strokeexhaust system, or more accurately the expansion chamber system. As I understand it the way the engine designers get the fresh charge to stop before it follows the burnt charge out the exhaust port is through an acoustical wave or echo that is generated off the far end of the exhaust system. That echo needs to be timed to arrive at the engine exhaust port just as the last of the burnt charge exits and momentarily stop the flow until the piston skirt can close the port retaining the whole of the new charge in the compression chamber. Depending on what RPM you want the engine to run best at the expansion chamber dimensions, like length width and girth all have to work together for the echo to have the right timing. Spent charge then passes to a silencer or muffler at the end of this entire chamber doing all this acoustic wave voodoo. I have even have seen systems back in the 70s that allowed the tail pipe (stinger) to be varied in length to broaden the power band on 2 cycle racing kart engines; although, today they do this with mechanisms that in effect raise an lower the upper exhaust port lip in the cylinder wall which is even more effective for broadening the power band. Lawn mower 2 cycle engines running at constant RPM keep things simple requiring only a fixed set of dimensions for optimum efficiency and performance.

Before I get too far off on a tangent, I too have wondered why they couldn't have done the under deck exhaust system and the only few things I could think of was that the added length of the transfer pipe found on DF motors helps with this acoustic timing issue and to try to make it all happen under the deck left to little room for the blade and mowing process. It could have been simply a matter of lower cost to implement and upper deck exhaust system as well. Or, more likely, some corporate lawyer at Toro felt that if the under deck exhaust ever caused a grass fire it would be too easy for some ambulance chaser to point out no other lawn mower manufacturer does it that way and therefore it was not a safe design. Anyway, I do miss the mellow hum of the under deck exhaust with the occasional waft of exhaust smoke coming up off the turf as you mow along.


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RE: Duraforce Re-jetting Instructions Part 2

I got my 10424 back from the shop today. I took it in a few weeks ago to fix a carb leak that drained the fuel tank and flooded the engine. They put a new carburetor on it to fix this issue.

With the new carb, my 10424's DuraForce runs like a dream---no surging at either idle or full throttle. I mowed with it and noticed that the exhaust also sounds a little different. It's got a raspier note to it that I enjoyed listening to.

Upon close inspection, I discovered that the part number on the new carb is different from the part number on the old one. The new one is part number 98-7000, while the old one was part number 98-7042. Does anyone know the reason for this? I thought that all DFs had the same carburetor. The difference in part numbers, along with the dramatic improvement in performance, makes me wonder if maybe there's a commercial DF carburetor. Is this correct?


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RE: Duraforce Re-jetting Instructions Part 2

Sounds like it to me, tarheelman! It would be verrrry interesting to measure the jets in that carb! (hint hint!)


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RE: Duraforce Re-jetting Instructions Part 2

Actually that is the old original number. It has been superceded by the 7042. I found this out when a 7000 came up on Ebay for sale (an auction that ended a couple hours ago) and I ran the part number on RCPW days ago before posting my bid. The number came back as superceded by the 7042.


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RE: Duraforce Re-jetting Instructions Part 2

FordTech--

Thanks for the info. Any idea what the differences between the two carbs are? I don't understand why the performance with the new carb is so much better, especially the lack of surging. Did your '98 10424 have the 98-7000 carburetor on it when you got it? If so, how did it perform?


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RE: Duraforce Re-jetting Instructions Part 2

No, it has the 7048 and ran pretty pathetic. I have no idea when the 7000 was used or in what mowers specifically, just that at both SEPW and RCPW the 7000 is superceded by the 7048. Maybe that they used both and finally did away with the 7000? Who knows.. Of course Ive only had the 10424 a year so it may have had a carb replacement.

I lost the auction in the last 10 seconds by a snipe bid so I wont be able to tell now if there is a difference. Maybe there was just a problem with your carb or the sealing of it.


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RE: Duraforce Re-jetting Instructions Part 2

FordTech--

You might be right. My old carburetor might have had an air leak somewhere. However, I still don't see how the new carb could've completely eliminated the surging like it did if there's no difference in the jet sizes between it (98-7000) and the old carb (98-7042).


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RE: Duraforce Re-jetting Instructions Part 2

float height could be playing a role in the surging.


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RE: Duraforce Re-jetting Instructions Part 2

Maybe the shop went ahead and re-jetted the carb before they put it on, tarheelman? Good point about the float height, could definately play a major role in the running.


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RE: Duraforce Re-jetting Instructions Part 2

Two Cycle Nut--

I hadn't thought of float height, but it makes sense. That could be the difference---a more precise float height setting.


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RE: Duraforce Re-jetting Instructions Part 2

I stand corrected on my two mowers, both have the 98-7000.


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RE: Duraforce Re-jetting Instructions Part 2

yo saxman,

what's the verdict?


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RE: Duraforce Re-jetting Instructions Part 2

Update
While waiting for the jets I ordered for my brothers 10552 to come in for his re-jetting I tweaked the jetting on my 10550.

I opened my pilot jet to accept a #77 bit from the #78 I had done before and kept my main jet at clearing a #67 bit. My first re-jetting was very close to perfect with only a slight hint of being lean and this nudge on the pilot was all that I needed. I felt if I had gone to a #66 bit opening on the main jet it would have been too much and since the pilot feeds fuel at all throttle settings it was a good way to tweak the jetting slightly more rich. I tested it today with conditions of 74 F and 52% humidity. I think Milwaukee is about 300 to 400 feet above sea level, (I'm not too sure about that).

Now my Boy's jetting is about as close to perfect as you can get with a fixed jet carburetor with the engine no longer surging at any throttle setting and will burble when there is no or little load and clean out nice in when mowing. Idle speed is still fine with no excessive exhaust smoke. I did a full throttle spark plug check and it came out on the grayish side of golden brown on the electrode insulation. I was pleased to see that. I do use more fuel now (duh) as I need to refill the tank before I finish mowing and I didn't need to do that with the stock jetting. So what, the mower runs like a Lawn-Boy should run now.

I'll post an update about my brother's outcome when the jets come in and I get them reamed and installed.


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When this topic was first posted, I was very skeptical. My Dura Force Engine ran well and didn't surge, so why go through all that hassle. I didn't dread drilling the jets, but after working mostly with the older LawnBoy Engines, I just hate these newer ones, even though it's only the carburetor. So not being one to resist progress, I ordered new jets. I wanted to keep my old ones , just in case, because I've learned through the years, that Murphy's Law is always out there. Whenever I went to pick them up, yesterday, the mechanic told me that these jets were the "New and Improved Models" and made it sound like they were Gods Gift to the Dura Force Engine. The jets were larger and they would cure all ills. Yeh, right, the bits that I was going to use came nowhere close to fitting into the openings. Some difference. I started with the main jet and it went like a dream. Used a very high speed, lots of cutting oil and took it very slow. The low speed went just as well, but I was scared to death I would go too far, so I marked the bit with a piece of tape and everything went well with that one too. Now all I have to do is to motivate myself to tear the thing apart take out the old jets and install the new ones. I think I would look forward more to giving the dog a bath than tearing that thing apart and then putting it all back together. I just hate the thought of having to fool with the throttle cable, governor, gasket, heat shield, and getting the bolts aligned so it would all go back together. I sure hope it's worth it. I think I will make this a winter project. That way I will have several months to get myself motivated.
Oh. by the way, anybody that read my last post on the subject of the mystery engine, I got my honey do list completed with time to spare.
Bill


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RE: Duraforce Re-jetting Instructions Part 2

Now that was like telling a great suspense story and then telling us you will tell us the rest in December.. damnit!


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RE: Duraforce Re-jetting Instructions Part 2

Patience is a virtue.
Bill


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RE: Duraforce Re-jetting Instructions Part 2

Bill,

You don't have to disconnect the throtle cable or the governer mechanism. If you remove the belt cover below and pull the green engine cover above access is good enought to leave the whole carb assmebly as one piece. Just leave the mounting screws in place from the air box to mounting flange to hold it all together. It takes less than an hour, unless you drop the main jet down a cold air return duct...then it yakes 2.5 hours :[

My 10550 didn't surge either, but it sure was running lean. Over the 20+ years I intend to keep this mower, I figured it needed to be richened enough to not burn it self out in 5 to 10 years. EPA be damned.


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RE: Duraforce Re-jetting Instructions Part 2

Well, I guess I am going to bite the bullet and write another chapter in my suspense story, and replace the low speed jet, since it does not require much effort.
There are two questions I have. 1. My shop manual states that one drop of loctite should be put on the threads before re installing them. Has anyone else done this? 2. Does the decal that covers the low speed jet come off easily, so that it can be put back on, or do you have to get another one, or just simply leave it off?
Bill


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RE: Duraforce Re-jetting Instructions Part 2

Bill,

I didn't use any loctite for the installation of the reamed jet. I omitted this as I was worried about the ability to pull the jet again if needed for fine tuning. A light snugging should be fine but be careful as brass is soft stuff. I will try it this way for a while and maybe Loctite it after I am fully satified with the jetting.

The decal peels back easy enough and I only peeled it about half way to expose the piolt jet opening. Do it with very clean dry fingers, or it won't adhere again. I didn't and had to use a little contact cement on the back of the decal to make it sticky again.


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RE: Duraforce Re-jetting Instructions Part 2

OK,
Slow speed jet installed, main jet to go.
As I stated, I didn't think my 22261 ran that poorly to begin with, so with just the slow speed jet installed, I don't know if there was any noticable inprovement. The only thing I could have done was to make a sound recording before and after and then compared the two. Maybe I will do that before I install the main jet. I guess I am looking forward to doing this, but I will have to wait until I get my hoist freeded up . My back has seen too much lifting and working while bending over, that I don't do anything anymore unless I can put it on the lift so that I can sit and have it at arms length.
Will keep the group informed.
Bill


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RE: Duraforce Re-jetting Instructions Part 2

Finally completed the re-jetting. As I mentioned in my other posts, I didnt think my dura force engine started or ran that poorly to begin with, so to make a constructive comparison is difficult. I can, however make some observations. 1. Engine does smoke a little more. 2. Starting is still the same. Prime once or twice, apply choke; starts on the first pull. 3. Increase in power? Prior to the re-jetting, I never really tested the unit for brute power but after the re-jetting, I thought I would give it a try. After it had thoroughly warmed up I took it through a section of hay field where the grass was knee high. It didnt even hesitate. That gurgle that is talked about turned into a powerful sounding hum and it proceeded to mow continuously with out the slightest hint of wanting to stall.
Is re-jetting God's gift to the Dura Force? I honestly couldnt say. All I can do is to present my observations. The one aspect of the re-jetting that might not be obvious is the fact that it will probably run a little cooler, which is a good thing.
Bill


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RE: Duraforce Re-jetting Instructions Part 2

With this draught, I have not used my re-jetted 10424 for over a month and had used it only ONCE after the re-jet. Finally got out and cut the grass today and was wondering if anyone else's Re-Jetted Dura-Force does this ...

Upon re-start (warmed up), engine "races" initially. Not sure how high an RPM it peaks at, but it is much higher than normal.

Neither my old 1999 vintage 10323 OR this 2003 vintage (but bought new this year) 10424 did this before the re-jetting.

My re-jetting consisted of the Suzuki Pilot Jet, Main Jet drilled to #67, and adjusted the govenor 1 click slower.

Once it settles down, normal engine speed sounds about correct ... I also bought a Tecumseh Vibra-Tach, but have yet to use it.


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RE: Duraforce Re-jetting Instructions Part 2

If one of you happen to knarl up a perfectly good carburetor, I have now aquired 3 used ones for spare parts. Two that have arrived to day are 98-7000 and one coming in is supposed to be a 98-7042


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RE: Duraforce Re-jetting Instructions Part 2

I had also added a Stens 90Deg fuel shut-off and small B&S fuel filter during the dry spell. After a few minutes of cutting (engine wamed up) I noticed it was suging worse than it did before the re-jet. Only thing I could think of was the fuel filter was too restrictive. Pulled it out of line and it then ran normal.


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RE: Duraforce Re-jetting Instructions Part 2

Interesting. That gives some credence to the theory that the fuel tank makes some contribution to the smoother running commercials. Simply a fuel flow/pressure change makes the difference?


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RE: Duraforce Re-jetting Instructions Part 2

I have a filter on all three of mine now with no restriction. I used a larger B&S filter.

Regarding restricted fuel flow I have been mentioning...has anyone noticed the nipple on the end of the non commercial tanks? Both my 10323 and 10550 were hardly open at the end with a small nib of plastic restricting the hole from the manufacturing. Only about 20% of the nipple was actual free and open for gas to pass through. It appears when they chopped off the end of the nipple, it squeezed the plastic shut a bit. I would assume the plastic would be hot and it just pinched close a bit. This coupled with small jets = surging!! The higher tank with the gallon of natural head pressure, may be the reason the commercial units run better. The commercial nipple has a brass valve inside it and held tight with a hose clamp. This would make perfect flow through the intake of the brass valve.. I also am under the belief, the engine shroud is causing a difference in air flow affecting vane operation. Everything else in the mower is the same.


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RE: Duraforce Re-jetting Instructions Part 2

Yes, it certainly seems logical that the larger tank would supply more pressure as would it's increased height in relationship to the carb inlet. Correct me if I'm wrong (have never seen a commercial model up close), but it appears that the bottom of the tank is higher than that of a regular Duraforce.

What made me think "fuel filter" was something stated in an earlier thread. Someone had installed a large clear filter in-line that appeared to have a pleated paper element inside. Someone else came back saying that type of filter should only be used on engines with a fuel pump ... using it on a gravity-fed fuel line could cause irratic engine performance.

The filter I used is a red B&S ... 1.37" dia. x 1.75" long o/a and appears to have just a simple screen inside it. I had used a screen type filter on my 10323 for years with no problems ... it was white plastic with two halves held together with one center screw that allows ports to be rotated for best fit. It is just I now wanted to add a shut-off AND a filter and this little red B&S was a 1/2" shorter and seemed to be the ticket. Looking at it now, I think there is room for this slightly longer filter ... but what difference can it make, they are both screen type filters that should have similar screen surface area !! The shut-off can't be all that restrictive, but maybe the combination of it AND a screen filter is. Many on here have added filters, but I think I may be the only one on here that has tried to do BOTH !!


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RE: Duraforce Re-jetting Instructions Part 2

Yes, the tank on the commercial sits higher than that of a standard duraforce. However, my commercial surged like crazy when I first got it. I did the rejetting on mine and now it runs like a charm. I agree that there would be a less restricted flow of fuel to the carburetor with the larger tank and the brass elbow but it didn't help mine at all. It surged like heavy footed driver in bad traffic. It was an embarassment. Now it runs well. I can't believe that the commercials would have been given special treatment over the other duraforces. Same engine, same EPA standards to meet. In fact, I was at the dealer the other day picking up a gator blade and asked the guy there about the surging (I had already fixed mine) He said that that is the number one complaint about the duraforces and that everyone used to mowing with an older boy immediately thinks there's a problem with their new mowers if they've bought a duraforce. The mowers on the two engines are essentially identical, aside from the shroud and tank. I said before in a previous post that it must be a slight difference in the bore of the jets on a minority of duraforces that accounts for the mystery non-surgers. Think about it, all it takes is 1/1000th of an inch to turn a surger into a non-surger. This could easily happen during the manufacture of the jets. It would be an acceptable percentage of "defects" (hardly a defect, I know) produced. All things the same, each duraforce should run the same. Everyone who has had a surging duraforce (at least on this forum) have all looked to the carburetor and fixed the surging by oversizing the jets. All I know is my experience with my commercial and it surged like an S.O.B. until getting a jet-job. Aside from the fuel flow being VERY restricted due to a manufacturing error in the tank, or a plugged filter, I can't see how it could be anything else but the jetting.


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RE: Duraforce Re-jetting Instructions Part 2

I used the pleated filter mentioned on all my Duraforces after I rejetted them. I found too much junk at the main jet screen filter in the carb to feel comfortable with leaving as is, so I installed in line filters. They work great. The Briggs package never mentioned about fuel pumps...just said for all horsepower engines. These filters are better than the screens. The picture below is from a in line filter installed on my 10550.


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RE: Duraforce Re-jetting Instructions Part 2

i installed the red briggs filter and a shutoff on mine too. no problems but i did have troudle with the white 2 peice filter doug recommends-it leaks! also the new carb i got has the older 7000 # on it but runs like a champ . so much for the theroy that the newer7042 is a newer and better desighn


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RE: Duraforce Re-jetting Instructions Part 2

As cheap as those little white 2-pc filters are (and no gasket on screw if I remember correctly), I'd expect them to leak too. But I don't think it ever leaked for me.

Since mowing this weekend, I've removed the gas tank to check for plastic obstruction in the hose barb (as others have mentioned) and found mine to be fine. I then re-installed my fuel line putting in the white 2-pc filter to see how that does.


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RE: Duraforce Re-jetting Instructions Part 2

Tom P PA, Back on July 20th you said you were thinking about increasing your jets one more size on your 10550. Just curious if you did this - what sizes are your jets at this point and are you staying or going up?

I'm rejetting my 10550 this weekend and would like your input.

Thanks.

Greg Meyer


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RE: Duraforce Re-jetting Instructions Part 2

I suppose it's time for me to chime in. Today after nearly 7 years of use, my '98 10324 Lawn-Boy decided to continually and consistently surge when not under load. In all the years I've owned it, I've never had a problem with the mower.
I took the air filter out and dismounted the carburetor to find that a lot of dirt had gotten sucked around the back of the filter and into the carburetor. As a result, it was pretty dirty, but I gave it a thorough cleaning.
My question is would it be wise to replace the jets with a stock set or should I also be re-jetting the carburetor like others? Like I said, it's been running great for all these years..no problems other than this one now.
What do y'all think?

Thanks.

PS - Hope I'm not doing anyone a disservice by posting this message in this thread, but I thought it was somewhat related.


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RE: Duraforce Re-jetting Instructions Part 2

I would not replace or alter the jets if you are satisfied with the way it runs, assuming it runs the same when you get through with it.


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RE: Duraforce Re-jetting Instructions Part 2

Greg, if you are not aware, please review the first 100 responses on "Duraforce Re-Jetting Instructions." This is actually Part # 1 and has a wealth of information. Print it before it gets removed from the site. The procedure is very simple.

I never went up to a larger bore yet. I will do it at some point, but I have not had the time as of yet. Just became too busy.

The 10550 runs a world of difference better than pre rejetting, but I am confident I can improve it by going up one more on each.

In regards to the pilot jet, a #79 bit fit my stock jet, and I bored one bit larger with a #78 bit. In regards to my main jet, a #69 bit fit my stock jet, and I bored one bit larger with a #68.

My bits were "cheapie" ones on ebay and am guessing they are off tolerance. I believe on most main stock jets a #68 will fit and you should bore with a #67.

Regardless, just see which ones fits, and go up in size.

If I had to do it over, I would go up 2 on each. I think I get get some more gurgle and burble sound out of it.

The stock Duraforces run way too lean. My engines run remarkable cooler now, which has to increase its longevity.


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RE: Duraforce Re-jetting Instructions Part 2

Please explain how you know the engine is now running remarkably cooler. I know there are such things as remote thermometers, is that what you used?
Bill


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RE: Duraforce Re-jetting Instructions Part 2

Tinkerer, I dont know what Tom uses but the common tool today is the laser thermometer. These are sold in abundance on Ebay.

Here is a link that might be useful: laser thermometer


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RE: Duraforce Re-jetting Instructions Part 2

Much easier method. After I mow my lawn, I lick my finger and then touch the engine head just just below the spark plug and count how long it takes until it starts to hurt. Before rejetting 3 seconds. After rejetting 8 seconds. See, it runs cooler. LOL.

Actually, after I use my mower, I hose down the top deck and then flip the mower on its side and hose the underdeck portion along with some hand assistance on removing clumps (I find this more effective than running the engine and spraying the hose under the deck). I then wipe the top of the deck down with a towel.

I noticed the "hissing" water sound hitting hot engine parts was reduced. And when wiping down, I noticed the engine was much cooler. I use an old tee shirt on the deck and on the exposed engine base below the shroud. You can feel the heat on the face of your hand.

So I guess you can say my observation is based upon sound and touch.

Now that you mention about thermometers, it would be an interesting study to actually measure before and after rejetting for those who have not rejetted.

One can easily take a bulb thermometer and hold it to the side of the mower using some sort of clay over the top of the bulb to hold it onto the engine. Mow your lawn and then take several measurements after a specified running time. This should be done over 2 or 3 weeks so we get enough data. After rejetting, do the same measurements.

Any pre rejetting takers ???


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RE: Duraforce Re-jetting Instructions Part 2

The Laser Thermometer is what I was thinking about. I would be interested it hearing the results if someone has one of these and would be able to take temperatures, while engine was running, before and after re-jetting.
Bill


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RE: Duraforce Re-jetting Instructions Part 2

I agree, my engine is totally running cooler. My engine used to be scorching hot upon shutting it down after an hours running time. You can feel the radiant heat off the engine. The reduction is noticeable to me.

Also, someone posted an article from a magazine that analyzed the Toro Duraforce when it was first introduced. I recall the article saying the engine ran leaner and hotter and some extra cooling fins had to be added to reduce extreme heat. It is no secret about Toro purposely creating a lean engine.


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RE: Duraforce Re-jetting Instructions Part 2

Pilot jet is it the idling speed or the low speed jet your talking about

Thanks
Jerry


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RE: Duraforce Re-jetting Instructions Part 2

A pilot jet is the same as a low speed jet. It controls low speed fuel/air mixture. An idle screw adjusts idling speed.


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RE: Duraforce Re-jetting Instructions Part 2

Bumpitty bump-bump!

This post has been quiet and someone recently mentioned re-jetting his DuraForce. I would hate for this valuable knowledge to be lost!

Happy mowing!

AJY


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RE: Duraforce Re-jetting Instructions Part 2

that would be me. as soon as i grab some new parts, i am going to test my DF out and see how the surge is... especially after a good carb cleaning. if it still surges as badly as it does (a # 98-7000 carb) i am going to find a bit set and have at it. i have the zuki jet already, so i may just swap it out and only rejet the one instead of both. have not decided yet. for my memory, anyone have the part numbers for the two LB jets and the zuki jet? is there also a great place to buy a bit set that has a good price AND decent quality? eBay makes me nervous with their great prices, but if i recall, didn't someone have a bad experience with them?

Rangers


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RE: Duraforce Re-jetting Instructions Part 2

On pre-compliant engines, a mixture screw (needle valve) was used to control mixture. This was very handy, as you could enrich the mixture for more power in hard cutting conditions or just make little adjustments as the climate changed with the seasons. Many early post-compliant engines continued to have the needle valves but with limiter caps on the screws like on cars in the '70s. If you could find an early carb like this that would fit, the Duraforce would be cured for good.


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RE: Duraforce Re-jetting Instructions Part 2

Saxman...did you ever re-jet? Curious as to your findings if you did.


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RE: Duraforce Re-jetting Instructions Part 2

suzuki 2 stroke part number is 81-1030
standard main jet 98-1357
standard pilot jet 98-7041

Don't bother drilling out a standard jet, splurge and get the 'zuki jet. It makes the job VERY simple. No worrying about broken bits and all that.

I got the bit I needed from a local hobby shop. They were excellent quality and were kept in little vials behind the counter. Another place with decent quality is tower hobbies. (see link) They also sell pin vises(an absolute necessity) and individual bits.

If your machine surges and you are hesitant to take the "re-jet plunge" don't be. It was the best thing I've done to any of my outdoor power equipment. Even at high noon when it's 100 degrees and 99% humidity my LawnBoy puts a smile on my face! And re-jetting one of these things isn't hard at all, it just sounds a little intimidating!

Here is a link that might be useful: bit set


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RE: Duraforce Re-jetting Instructions Part 2

Thanks to everyone for all of the info! Rejeted 2004 Duraforce last week. It's a lot more fun to use now. Redrilled orignal jets and reused all gaskets. 67 & 78 It will now start without primming.
Larry


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RE: Duraforce Re-jetting Instructions Part 2

Hi everyone,

Thank you Tom P for this post. I just bought my first silver series dura-surge, and i cant wait to re-jet it. Why does the post recommend buying new Jets? Why not drill out existing Jets? I see that HRZ03 did this, did anyone else try that? I am very inclined to take this route, no sense to me throwing more money at this than is necessary.

Please advise.

Lawwnbboy...


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RE: Duraforce Re-jetting Instructions Part 2

There is no need to buy new jets or gaskets - just drill out. You do not need a pin vise either, just pliers to hold the bit as you are just drilling brass. A good starting point is to drill only 1 size larger on both jets - see how it runs then. A warning, if you have a set of drill bits do not get them mixed up as they are very tiny.


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RE: Duraforce Re-jetting Instructions Part 2

"There is no need to buy new jets or gaskets - just drill out. You do not need a pin vise either, just pliers to hold the bit as you are just drilling brass. A good starting point is to drill only 1 size larger on both jets - see how it runs then. A warning, if you have a set of drill bits do not get them mixed up as they are very tiny."

Thats what I was picking up. I hear you oud and clear on all 4 of these points. Thank you.


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RE: Duraforce Re-jetting Instructions Part 2

The one bit is so small...just be patient and use some oil. It feels as though nothing is happening, but all of a sudden, it "breaks through" and you are done.

Mine too, no priming anymore, may be once at times, but not 5 or 6 like the old days.

Did Saxman ever re-jet yet??


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RE: Duraforce Re-jetting Instructions Part 2

Woo hoo!! I got my drills and vice!!

I will be drilling tonight...


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RE: Duraforce Re-jetting Instructions Part 2

There is also a Part One....but not sure if it is still around anymore. Many helpful tips.


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RE: Duraforce Re-jetting Instructions Part 2

Help. Please.

I got my drills last night, and began the re-jetting. After removing the carb, i found, i think, the main Jet. The main jet is the one that feeds into the carburetor 'throat'. is this correct? i bored this out using the 67 then 66 wire gauge drill. mission accomplished.

Then i started looking for the pilot Jet. its nowhere to be found. is this possible? what is a pilot jet? where is the pilot jet? is it the inlet Jet from the gas tank?

of course i reassembled the mower last night expecting the surge to be gone, but it was just *slightly* still there. :(

thanks in advance guys.

Lawwnbboy.


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RE: Duraforce Re-jetting Instructions HELP Part 2...

BTW, the mower is the 10247, silver series push...


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RE: Duraforce Re-jetting Instructions Part 2

Look on the side of the carburetor, you will see a sticker with some mumbers. With clean hands, carefully peel the sticker back. Directly underneath is the pilot jet. It controls the idle mixture. After the rejet, put the sticker back on. You should not have to remove the carb to get to the pilot jet.


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RE: Duraforce Re-jetting Instructions Part 2

OH YEAH. Thanks snuffy!!


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RE: Duraforce Re-jetting Instructions Part 2--YUP

Thanks for all the pointers guys, my mower is running very nice now. Mine was a trade in to a local lawn mower repair shop, and all it needed was gas and a re-jetting. It cost me $25.00. A good deal indeed.


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RE: Duraforce Re-jetting Instructions Part 2

May be saxman will re-jet ??


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RE: Duraforce Re-jetting Instructions Part 2

Lawwnbboy, Good to hear all is ok in the 2 cycle lawnboy world. What size did you drill your pilot jet?


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RE: Duraforce Re-jetting Instructions Part 2

Thanks bigal_mo, it is good. something else i did after re-jetting was to take the mower and drop it onto a pile of leaves which accumulate on my north facing wall of my house, it didnt even slow down. this beast is strong.

I drilled the pilot jet with a 78 wire gauge drill. the vice that i bought couldnt even grip it so i had to eventually take the drill bit, hold it with pliers, then holding it still i twisted the pilot jet onto it slowly. i didnt break any bits during the process. it got hung up a few times but i backed out and redrilled over and over until it broke through. a very simple process.


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RE: Duraforce Re-jetting Instructions Part 2

Hi. I just wanted to revive this thread for a bit more clarification. I copied the url for the parts list of my 10323. I have the wire drills bits and am ready to rejet, but wanted to know why the pilot jet is not listed in the parts list. The part number (98-7041) is also not listed. The mainjet is clearly identified and is not a problem, but is there another name for the pilotjet. Slowspeed, idle and 37.5 also do not appear. Does the 10323 simply not have a pilotjet? I haven't looked behind the sticker on the carb yet, so I have no idea yet. Thanks in advance.
Regards,
Stevan
Here is the Link:

https://lookup2.toro.com/request/getpub1.cfm?PubID=13009&PubNum=3321-570&Lang=EN&Cust=anonymous_user&xCaller=lawnboy&Filesize=2394941&vKey=1983392&PubType=11


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RE: Duraforce Re-jetting Instructions Part 2

and part 2


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RE: Duraforce Re-jetting Instructions Part 2

Thanks very much to the guys that provide the info above, particularly the specifics on how to drill out the carb jets. I was having nothing but grief with my Lawn Boy. I finally followed the above instructions and added running a drill through the fuel tank outlet to make sure there was no fuel starvation issues and installing a fuel shutoff and Briggs in-line fuel filter. The formum that deals with the air vane throttle operation was also helpfull. Once all this was done, the engine started on the first pull, which it hasn't done in years and has a new healthier sound to it with lots of rpms and power.
So thanks very much guys, your info was most helpful.


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RE: Duraforce Re-jetting Instructions Part 2

Many thanks to FordTech and the forum for posting these instructions. My DF 10550 lives again! I had a real bad engine speed surging problem that was really annoying. I followed the instructions on drilling out the carburator jets--it now works perfectly, runs like my old lawn boy that I used for 22 years with that happy two-cycle sputter when not under load.
I enlarged the pilot 0.002" (from .014 to .016") using a #78 wire gauge drill and the high speed jet to .033" using #66 wire gauge drill.


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RE: Duraforce Re-jetting Instructions Part 2

I know it has been a while since these postings, but I just now discovered this great site. I have a Lawnboy 10252 with a 107-4607(98-7042 old number) carb. Mine has all of the aforementioned problems and I wondering if I could re-jet mine to these specs. If not, do you think I could perform the 10% increase in regards to the pilot and main jets if my stock sizes do not correlate to the above carbs?
Thanks for any help you can throw my way.


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RE: Duraforce Re-jetting Instructions Part 2

I received my bits today, and the go/no go specs worked out for this carb. as well. Wish me luck.


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