Lawnboy Re-Jetting, What's The Latest Info

leeave96(VA)February 4, 2007

I'm getting ready to remove and clean the leaky carb on one of my Lawnboy 10550's and thought I might try re-jetting it, but I have a few questions.

1. What is the latest on rejetting?

2. For the pilot jet, should I drill it, buy the Mikuni jet (p/n 81-1030) or use the R-Tek (p/n 98-7025 or B&S p/n 801308)?

3. What about the low speed jet? Are you folks changing out that one with a replacement jet (if so which and what part number) or drilling it out or leaving it alone.

Thanks in advance,


Thank you for reporting this comment. Undo

The low speed jet and the pilot jet are the same jet. The other jet (main jet) should not be drilled. If you have the drill bit try drilling. There's nothing to lose. The Mikuni jet seems to give the same results.

    Bookmark   February 5, 2007 at 9:00PM
Thank you for reporting this comment. Undo

Looks like all the rejetting info fell off the forum.

Here is what I would do. Get a set of tiny drill bits number series #61 thru 80 (search ebay drill bits #61 - 80).

Take the main jet - find the largest size that will fit the hole. Drill the next size larger. The main jet is inside the carb.

If this does not give what you want. You can drill the pilot jet. This is accessable on the outside under the carb id sticker.

If it still does not give the 2 cycle burble, you can drill the main one more size larger.

All the jets are available at Toro/Lawnboy so if you mess up you can start over.

    Bookmark   February 7, 2007 at 9:04AM
Thank you for reporting this comment. Undo

Evaluate the performance of the engine prior to the carb leakage to determine what changes if any are required. Now that that's out of the way, going up one drill size on the main jet and one size on the pilot jet worked for 2 of mine. On the 3rd I had to go up 2 sizes on the pilot jet. Modifing the pilot jet is going to effect the idle whereas the main jet controls the mixture under engine load. If you get the drill bits also get a "pin vice" to go with the set (handle for the bits, looks like a screwdriver). Don't drill all the way through the pilot jet, just the end that goes into the engine first, continuing until the bit reaches the cross drilled holes. Don't let the drill take too big a bite into the hole or it will thread in like a screw and break. Blow the metal chips out with carb cleaner and go. Let us know how it went.

    Bookmark   February 7, 2007 at 10:23AM
Thank you for reporting this comment. Undo

Here is a little blurb I copied off the forums a couple years ago.. forgot who the original author was..


The Low speeed jet is a 37.5.
The High speed jet is a 77.5.
The high speed jet is located inside of the float bowel. Remove the "fuel filter" screen and you will be able to see it. It is screwed into the larger nozzle.
When I tweak one of these engines for someone. I will start by getting two new stock jets. Then drill the low speed to 38 and the high speed to 78 to start. Then go .5 larger at a time until the surging stops. When that is achived. I will go back and drill the main jet out +1 oversize as I did the low speed jet.
If I drill the low speed jet from 37.5 to a 39. Which is 1.5 larger.
I will add 1 to that 1.5 which of course is 2.5. Then drill the main jet and take it from a 77.5 to an 80 jet.
If you have surging at idle. What do you think is happening when you apply full throttle where you do most of the work? The funny thing that I have saw with many DuraForce engines when working on them. When the head is removed. The cylinder and the top of the piston are dry and the cylinder is a dull flat color. Which is mostly caused by a lean condition or running to hot. Then once I have rejetted the carb to where they are running a richer fuel/air mixture. The cylinder and piston top become shiny and damp looking from the extra oil that is reaching the parts after running for awhile.
The normal rule of thumb when dealing with a 2 stroke engine rejetting. 1 size up on the low speed jet, 3 up on the main jet. You do not want to have a rich low speed (idle to mid prm range) dumping fuel into a lean top end (mid to top RPM speed). You must achive a balance with the fuel system.
Once the carb is rejetted correctly. You will have a very happy engine that will run much smoother, cooler and provide more power to the blade.
The 5 or 6 that I have rejetted for people here have been very happy with the results. Even with their fuel comsumption going up a little. But who is really going to complain because it now takes 36 oz of fuel to mow the same area that use to take just 32 oz? Not me when I know that my 2 stroke mower will not burn up and be around to mow another day.

    Bookmark   February 7, 2007 at 1:39PM
Thank you for reporting this comment. Undo

Most of the surging problems were cured by pilot jet drilling only or replacement with the Suzuki jet. The pilot jet is the primary low speed mixture jet but it contributes to the overall high speed mixture. It's effect isn't as pronounced as the main jet but it has a small effect and that's all you want to do is make a small mixture adjustment. Do one thing at a time tyhen test it at full operating temp before proceeding to more mods.

    Bookmark   February 8, 2007 at 8:47AM
Thank you for reporting this comment. Undo

If you are still under warranty try taking your mower back to the shop. Toro/Lawnboy has authorized warranty replacement of carburetors for surging problems. One of my 10550's was surging and was fixed with a carb replacement. Actually, I think a lot of the surging problems have nothing to do with the mixture being off from factory jets, but rather are do to air leaks from warped plastic carb. bodies and/or poor gasket seals.

    Bookmark   February 8, 2007 at 6:52PM
Thank you for reporting this comment. Undo

Ive seen them surge brand new out of the box.

    Bookmark   February 8, 2007 at 6:59PM
Thank you for reporting this comment. Undo

New here, first post. Just want to add my story. Found a new 10323 4 months ago at Mom & Pop hardware store. Ran perfect for about first 20-25 hours. Then began extreme surging. Droped off at respected lawn shop afternoon. Spent 30min. talking with "Factory Trained" Toro/ LB technician with 20+ years. Here is his story... not verbatim. In 2001-2002 they changed the carb to comply with EPA. Never had problems with anything sold or serviced before that. He will repair/replace my carb & add a fuel filter. Said it MAY not surge again for about 6 months. Then will most likely start surging again when a minute particle will work its way into the carb. His advice,1.Live with it 2. Move throtle into partial choke postition to minimize surging(claims he owns 1 himself and thats what he does) 3. Sell mower 4. Preform surgery on carb.(he refused to be ANY part of #4) My question to all of you. Is there anyway to replace jets (without drilling etc)? Possible to replace carb with an older style that never caused these problems?
Thanks for your time!

    Bookmark   September 4, 2007 at 8:41PM
Thank you for reporting this comment. Undo

The low speed (pilot jet) can be replaced without removing the carb. Try using the mikuni one if you can get it easily. If that isn't enough you could drill the main jet slightly larger. Not a big deal. Give it a try.

    Bookmark   September 4, 2007 at 9:41PM
Thank you for reporting this comment. Undo

Here's the link

Here is a link that might be useful: Link

    Bookmark   September 5, 2007 at 6:47PM
Thank you for reporting this comment. Undo

My neighbor, a very nice woman, who takes better care of her yard and home then most men can,has a Lawnboy 10550.

The mower's engine was running very rough when I helped her start it this PM. It was slowing up, speeding up, and; it sounded like a carb or bad fuel filter to me? She said she had just changed the spark plug. She had mowed the yard about a week ago, and; she complained about starting problems. It sounds like the loudest weed eater when I first heard it about a week or so ago. Anyway, she is a great neighbor, and;I like to help if I can. She said she bought it from a friend. Any ideas are appreciated. TY

    Bookmark   April 13, 2009 at 9:37PM
Sign Up to comment
More Discussions
Husqvarna 150bt blower running lean - harder to start
Blower is taking 3 - 5 pulls to start when it used...
Honda Mower Problem-Backfire thru Carb?
I have a Honda walk behind that has been awsome until...
Anyone ever use an electric mower?
As you may know, ethanol in our gasoline is really...
Honda Harmony HRB215 HXA - Left Rear Wheel Problem (Hydrostatic Drive)
The engine on this mower runs great, but there is a...
Tom Boy Lawnmowers????
Has anyone seen or heard of Tom-Boy push lawn mowers????...
People viewed this after searching for:
© 2015 Houzz Inc. Houzz® The new way to design your home™