Craftsman LT 1000 runs rough, pops thru carb

cobalt327March 22, 2009

First, thanks for the opportunity to join the site. IÂve read many, many posts but havenÂt found an answer to my problem, so here goes.

Mower is a Craftsman LT 1000

Engine is a B&S 17 IC OHV

Family- YBSXS.5012VP 247826

The mower was absolutely fine last season. However, it was kept outdoors, in the open. (long story)

Upon recharging the battery (that will not hold a charge now) and emptying then refilling both the gas (fresh) and oil (oil level is correct) the mower will start and run on choke. After it runs on choke for a minute, it goes into a rich running condition, as would be expected and has done last year.

When the throttle is set to run (choke open), it will then will rev, drop rev, drop, and run roughly the whole time. Often it will stall, unless I put it on choke. Then it will clear, run fine briefly then go into the rich running condition again. When the throttle is again set to run the whole cycle is repeated.

With the choke open, it runs rough and pops through the carb every so often (not continuously, but every 5-10 sec.)

Using the choke, I can get it to smooth out and run almost correctly with the choke about 1/3 closed.

I watched the carb with the filter lid off and eng. running. There were intermittent pops through the carb, with a spit of flame occasionally. When shut off, I had a backfire through the muffler once, that hasn't repeated itself.

Removed and checked the plug. Had been brown, looking as it should, but after running it with all the popping and missing, the plug actually looked a little lean at the tip (whitish).

I removed the float bowl and found just a trace of corrosion and a bit of rust on the spring located in the bottom of the bowl. Cleaned it all and reinstalled the bowl. Runs about the same.

Removed the cowling and the flywheel was rusty. I carefully polished the rust away w/180 wet or dry paper. Checked the coil gap, it was about 0.008" from the flywheel magnet.

Removed the coil and carefully removed the rust from it, replaced and gapped with brass feeler back to 0.008" and its still running the same.

Checked the electrical plugs, all were clean and dry, 20A fuse fine, replaced it anyway as the plastic had become weak.

IÂm thinking the problem is fuel-related. Is there anything else that you all can think of that might be my problem? Any hints and/or insight with working on the carb?

I've done many carbs in the past (mower and auto) so going deeper into it isn't a problem and I have all necessary tools.

What do you real mower guys think? Anything to do with the solenoid at the bottom of the float bowl? I didn't check it for operation, I don't know how to proceed with checking it.

Thanks in advance, Mark

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Maybe a valve is slightly gummed up and sticks at times. Spray some carb cleaner down into the airhorn as it is running to help remove deposits. Seafoam added to fuel and oil help also. You should also be sure that all water is out of the system and that you cleaned well enough in the carb. I always run the line when replacing the fuel filter to get water/ debris out that was trapped behind.

    Bookmark   March 22, 2009 at 10:05PM
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Visit your local dealer and get the valve lash specs and any revised specs. Adjust your valves, it that doesn't work you might have a blown head gasket.

    Bookmark   March 22, 2009 at 10:29PM
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The fact that the plug shows a "whitish" color, AND you have intermittent "popping back through the intake", AND that you can "somewhat smooth out the running" by partially closing the choke, all confirm that there is not enough fuel reaching the engine. The plungers do sometimes get gummed up and reluctant to open fully (and sometimes, not at all). You can try removing the fuel solenoid and soaking the plunger tip in a small container of spray carb cleaner. Fill the cap from the can with cleaner and stand the solenoid on its tip in the cleaner filled cap. Prop it up so it can't fall over. Soak it like this for a few minutes then push the plunger into the solenoid body a few times. The plunger should have a slight resistance or spring pressure when pushing it in. It should pop back out when you quit pushing it in. Repeat the soaking and manual moving of the plunger a few times until it operates freely. You can "bench test" the solenoid by using a 12VDC source (the tractor battery will do) by connecting the body of the solenoid to the negative pole of power source and the wire lead of the solenoid to the positive pole of the 12VDC source. The solenoid plunger should retract into the solenoid body when 12VDC is applied, and pop out when the current is taken away. You might have to push in ever so slightly to get the plunger to retract because in some cases, the plunger will be sticking further out of the body with the solenoid removed from the carb than when it is installed. This is because the design calls for the spring to actually PUSH the plunger valve against its seat with a bit of spring pressure. If the plunger does not "jump into" the solenoid body as soon as you apply 12VDC to it, just give the plunger a little nudge to get the plunger close enough to the electromagnetic field for it to "grab hold of" the plunger. The plunger should remain retracted for as long as the 12VDC is applied. While you are into this carb, check to make sure that the main jet is not partially clogged or varnished up. It is also essential that you have a good, free flowing air filter in place as well. While in this case it appears that your engine is "starving for fuel", you must remember that the fuel is "drawn out of the bowl by venturi effect". If you do not have good FLOW (which equates to induction air velocity) through the air filter, the venturi effect will be weak and so will the volume of fuel. Another thing you want to make certain that the cooling shrouding and fins have not been converted to a mouse haven over winter. These critters will carry all sorts of stuff in to create their condo. This can completely block the air flow from the fan. Overheating will also create a "lean burn" condition (just before everything siezes up).

    Bookmark   March 22, 2009 at 10:49PM
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Hi all.

Mownie, I read your informative post as well as the other posts and took them all into consideration, and I want to thank you all for such a quick reply.

The plunger solenoid was retracted when I removed the float bowl from the carb- that is to say, the rubber stopper was at the very BOTTOM of the bowl, not extending up more than maybe 1/8-3/16" or so from the bottom of the bowl.

If I understood the post correctly, the plunger should- when un energized- be fully extended, so as to block flow to what I'm guessing is the main jet?

If this is the case, it would seem that the plunger has stuck in the retracted position.

If this is correct, could this have any bearing on the main jet being clogged?

When I had the bowl off previously, I held the float in position and manually worked it (carefully, so as to not force the needle valve against the seat). It started and stopped flow of gas through the carb as it should. (BTW, a big improvement over the brass semi-circle float on my older 11 HP Briggs).

Also previously, I used some carb cleaner sparingly on the front area of the carb, where I saw air bleed(s) (left side, looked very much like an air bleed orifice, on the right side was a hole w/o any brass insert- just a hole, so I don't know whether it was an air bleed or not). Had no effect.

Where is the main jet? With the float assembly removed, will it be centrally located above the plunger? Is it removable?

Thanks again, one and all!


    Bookmark   March 22, 2009 at 11:21PM
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The main jet is "downstream" from the solenoid plunger, meaning that the fuel must flow past the plunger in order to get to the main jet. It would probably be very unlikely for the plunger to become "stuck in the retracted position" because when the key switch is turned off, the plunger extends under spring tension to close and seal. What you may actually have observed is the point I was trying to make about how the plunger can extend further out when the solenoid is removed from the carburetor. If you thought the plunger came out a bit more after you "messed with it", it actually might have been stuck "nearly closed". This could happen if a lot of varnish had built up BEHIND the plunger (think inside the solenoid) and this varnish "captured" the plunger when it tried to retract. This is why I suggest doing a soaking, followed by a "manual exercising" of the plunger. The varnish can build up and limit how far the plunger can retract. The repeated soaking and manual exercising of the plunger will help get the deep varnish out of the solenoid tube. You can clean out the main jet by "spraying" carb cleaner through it (use the little straw that comes on the can) followed by running a fine steel wire (like UNPAINTED florist wire or the type of wire found on "parts tags" ). It is also helpful if you have compresssed air to "blow out" the passages (but you can get by just using the carb spray and a fine wire). Main jets are usually removable. Most of them will feature a partial slot (on each side of the central hole) for a screwdriver to engage to. You must be sure the screwdriver is sized just right! If your screwdriver is TOO SMALL, you might just wreck the slots without ever moving the jet. If your screwdriver is too big, you will "chew up" the bore that the jet lives in. Most of the time you can effectively clean out the jet if it is blocked with only varnish. If it has solid debris from rust or corrosion in it, you might have to remove it to affect cleaning.

    Bookmark   March 23, 2009 at 12:02AM
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Let me start over, in regards to what I'm seeing in the bottom of the float bowl.

Or, let me ask this: Does anything normally extend up from the bottom of the float bowl, with no power applied to the solinoid?

Because nothing does on this bowl. At the very bottom of the bowl, there is a rubber stopper. It does not extend up, it is at the bottom of the bowl, with no power applied.

If the jet is "downstream" from this stopper, it would be in the solenoid itself, I know this isn't the case.

Nothing has been messed with in regard to this solenoid/plunger/stopper. Only visually inspected up to this point.

It would seem to me that un energized, this stopper on the end of the solenoid plunger should be (power off) fully extended (pointing UP, towards the float assembly and main carb body. This is a sidedraft, if that helps to visualize it)in order to do any blocking of anything, jet or otherwise.

Then, when the power is applied, the extended plunger/stopper of the solenoid would be retracted back into the solenoid by the magnetic force of the solenoid, thus unblocking whatever it was blocking (I'm assuming it blocks the main jet).

But that is the position it is in now- fully retracted, plunger/stopper at the very bottom of the float bowl. No power applied.

Do you follow me? I realize my description may be lacking.

Are there any diagrams of the carb so I could quote you some nomenclature? In the meantime, I'll try to find a diagram, although I don't (at this point) know the make/model of the carb.

Thanks again for your time and knowledge!


    Bookmark   March 23, 2009 at 12:37AM
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Post the Briggs & Stratton engine numbers from the engine. Post model number and type number. Then we can look at the IPL on the B&S website for some (hopefully) clarification of the configuration on your machine.

    Bookmark   March 23, 2009 at 12:37PM
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Sure will. In my first post, I included the numbers that I found, sorry that they are the Sears numbers. My bad.

The numbers are:
Model- 310707
Type- 0137-E1
Code- 011206ZD

Thank you for your patience.


    Bookmark   March 23, 2009 at 3:34PM
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I have found the issue to be with the solinoid not retactinng, as was earlier suggested. I will correct this ASAP.

Thanks so very much for your help.

Sincerely, Mark

    Bookmark   March 23, 2009 at 4:10PM
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For those wishing to rid themselves of the solenoid, it can be removed and the bowl fitted with a metric bolt: 8-1.0 x about 8mm long.

Use the sealing washer from the solenoid with the bolt.

    Bookmark   March 24, 2009 at 8:58AM
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    Bookmark   March 24, 2009 at 1:22PM
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