Hello dmcknight.

Great job.

Keep those Lawnboys running and humming :)

Good day.

You ordered a B&S part? I always heard it was a Mikuni part.

Anyhow, good job glad to hear you have had some success with the carb job.

Thanks for checking in and letting us know how it worked.

Neal

Check the other re-jetting threads - B&S bought the rights to the 'E' engine for use on snow blowers, so they are now a great source of Duraforce parts, but you have to use their nomenclature/numbers. Ducknight replaced the pilot jet which has been shown to enrich the Duraforce across the operating range and relieve the symptoms of so-called 'surging'. In this case it's my thinking that since the mower originally operated properly and developed a lean surge after a year, that it developed a condition or mechanical problem that should have been addressed. Throwing fuel at a problem has worked to cover it up since the invention of the gasoline engine, but is not usually the correct repair.

so all of us that "fixed" our surgung duraforce engines by rejetting to a larger size have preformed an incorrect repair? all our engines were suffering the same mystery aliment and we just "masked the problem by trowing more fuel at it?

The other day I had to replace my rope in my lawnboy 10323 while I was doing that I went and change the pilot orfice,in my lawnboy same part # as above,and it ran great.

Jerry

In the last year or so I have drilled out jets on a couple of late model B&S which were too lean, prob. like that from factory as usual carb cleaning did no good. I used one number drill larger than what would just slip in....They both ran fine then.....
E T.....

'so all of us that "fixed" our surgung duraforce engines by rejetting to a larger size have preformed an incorrect repair? all our engines were suffering the same mystery aliment and we just "masked the problem by trowing more fuel at it?'

Maybe not, but remember, his ran fine for a year, then changed. Does that say to you that it needed re-jetting all along? Read my post - it's just the truth. You can make most anything run better by throwing more fuel at it, but is that really the problem? It's a case-by-case thing. Every mower is different.

if the duraforce problem of surging is fixed by slightly enlarging the jets -it shows they were to small to beguin with -in order to meet epa requirements. -this is the truth!lawnboys NEVER had this surging issue till the duraforce came along which was desighned to run on lean conditions to meet epa guidelines. there can be no other explanition for all of us who rejetted and the surging stopes. face it the carb desighn on the durafoce is faulty to beguin with and would benifit greatly from a more reliable needle /float/seat mechanism and a adjustable low speed setting for the jet but sadly this isnt so. a fuel shut off and better filter sys would have helped too. it s just a terrible desighn all in all

dmcknight, If I understand your post correctly, you simply ordered a B&S jet and dropped it in? No drilling required?

If so, I'm on the phone to the local LB dealer tomorrow. The used DF I bought seems to run well, with good power and the odd "ping" when running unloaded.

Did the new jet fix the "ping" as well as the surge?

Nevermind on that last post, I think. I found another post here that stated the fun with surging started 01, 02 model years when the tuning on the DF was changed to make it EPA compliant.

DF's built prior supposodly have no surging problems. Maybe that's why the 98 I just picked up doesn't surge, only pings and pops when running unloaded.

they never changed the tunning on the duraforce. i bought one in 98 and it surged right away. the dealer couldnt fix it and i got a refund.

It gets even more interesting, I spoke with a Lawn-Boy dealer that inherited the Lawn-Boy line via him being a toro dealer. Asked him about getting jets for rejetting. His response, "whaaaa?!?! Don't waste your time, the DF is JUNK, we do what we can just to keep them running and a lot of our customers end up trashing them." hmmm

Better luck with dealer #2.
"Is it surging?"

no. just pings when unloaded

"Then why do you want to throw money at and fix something that isn't broken"
because my understanding is that leaned out engines run hotter and that the lean condition is Lawn-Boy's solution to the EPA's heavy handedness.

"And who's fault is that, the EPA or LB cheaping out. Lookit, the surging issue is rare and the internet has a way of blowing things out of proportion. If the one you just bought is a 98 and it doesn't surge it was either good from the factory or a someone that knew what he was doing did the an update. Don't touch it and don't waste money UNLESS it starts to surge. If you're worried about a lean engine running hot, run synthetic 2-stroke oil."

So it's a good engine the way it is right now? The other dealer I spoke with said they're crap and I would have been better off buying a used boat anchor.

"Funny that, when a mechanic has trouble fixing something, it becomes crap. It's a good engine and if it starts to surge, which it shouldn't, because it doesn't now, we have the fix. Otherwise, keep your money in your wallet."

wow

the only crappy thing about the duraforce is the epa compliant plastic carb. its a execellent engine otherwise

I was out mowing my lawn the other day with my LB 10550 when a neighbor across the culdesac walked over and started chatting. He said the two stroke sound made hime curious, he said he hasn't seen a two stroke mower in quite a while.

Well, the guys kind of old and turns out he worked for the Rochester division on the QuadraJet carburetor. An engineer type and quite interesting to converse with. We got on the subject of the duraforce and its carb. problems, this is what he told me.

Jim, (that's his name) said the hardest design aspect with a carburetor is to achieve linear metering over the RPM range the carb. is going to operate at. Therefore, getting the carb to deliver the same gas/air ratio from idle to max rpm. He said this has been a sticky problem from day 1, with so many variables that the solution only came when carbs. were eliminated with computer controlled electronic fuel injection. In all probability, he went on, your duraforce carb. is poorly designed. Non-linearity alone could set up and oscillating cycle in its operation. In addition, the carb. may not be very compatible with the engine it is being used on. He also corroborated what saxman said above, enriching the mixture can mask poor design. He told me this after I told him many owners were drilling jets to improve operation.

Now, I am not trying to start anymore arguments on this issue. I just throw it out FYI.

quintus,

Your neighbor is correct, poor fuel/air ratio across the rpm operation band was a big problem for the machanical automotive carburators. Fuel injection solved all of that and gave us better fuel mileage and a lot less wear on the engine cylinders due to oil wash off. A fuel injection system on our LB's would be really nice but would cost more than the mower itself does now. What we really need is a quickly adjustable main jet on our carbs like the LB's of the past. I have an older LB that has a large thumb wheel on the top of the carb for adjusting the mixture for the best running on a day to day basis. I have found that with this D series engine it would not be a very good running engine without this feature. I have found that going from a high presure warm day to a cloudy low presure front type day that I have had to adjust the thumb wheel as much as 1/2 turn richer to get the engine to smooth out. Except for the flexing issues I don't have a problem with the plastic carbs.

http://forums2.gardenweb.com/forums/load/lmower/msg062221514040.html?100

I bought the last 2 stroke lawnboy from our mower shop in Orange CT. The last few seasons the motor surged. I refit and sized the pilot jet and main jet. The article was perfect. As of 5-11-2008 my 2 stroke lawn boy works like the old champions. The resizing of the jets provided a better fuel/air ratio making it run like a champ. Gotta do this to the carb. On hindsight the carb can be released with the 2 screws you get to in the air box. pull the whole carb assembly away just enough to turn the float bowl. unscrew 4 phillip screws get to the float bowl remove the small filter screen and change out the jet.
remove the sticker on the left side of the carb and remove that jet. Replace
carb. Now, You dont need to mess with the governor spring. attach carb with 2 screws from air box. DONE. Total cost 27.00. Dont loose the drill bits you buy. They are the thickness of hair. 30 min job. took me 1hr because I took the governor spring off and that messed me up.

I have a Lawnboy w/ the Duraforce engine. I bought it in 2005 and the surging problem began within a few months. One repair shop adjusted the carb under warranty and it ran Ok for a few months, then started surging again. It also would conk out after it got hot and would continue to surge and conk out every 5 minutes or so. I removed the carb, took out all 3 jets and cleaned them. The needle fell out when I turned the carb upside down and I'm pretty sure I put it back in the right way. Now the mower won't start at all and it would always start on the 1st or 2nd pull when it was cold. The primer doesn't seem to be doing anything, but I hooked it back up the correct way. It has a spark, so I think it's something in the carb. Is it possible to overtighten the jets, or not tighten them enough? How much should the jets be tightend down with a screwdriver? Does anyone know where I can get an exploded view of the carb? Any help would be appreciated. Thanks

I bought a used Lawnboy with the 6.5hp duraforce (model 10324) a few months ago. The owner said he had only used it 7 times, then let it sit for 2 years. It looked virtually brand new. Anyway, after cleaning it up and cleaning out the gummy carb, it would start and run, but surged like crazy at any speed. I just got done rejetting the main and the pilot jet per the instructions in these threads (#67 for the main and #78 for the pilot) and now it runs great. Nice and steady at 3100 rpm and no surge. A big, big thankyou to those who posted the instructions for the fix and to those who keep the thread going.

Instead of reusing the three gaskets that go on the two mounting screws, I cut my own gaskets out of oil/gas rated gasket material that I had bought earlier this summer at Advance Auto Parts for a chainsaw repair. A big sheet of the stuff only costs $5. I reused the carb bowl gasket since it was quite a bit thicker than the others.

Good to hear Nick. It could be that the new gasgets did as much to solve an air leak generated surge as the rejet.

Sax,

I rejetted my 10550 and the result was incredible! The mower surged from day one. After a few years, I decided to rejet, both the main and the pilot and WHAT A DIFFERENCE!!!!!!! This mower sounds and runs like the LB's of old, but with the power of the Duraforce - a great combo. I wouldn't have thought the difference would be that noticeable, but it really is.

My question is - do you still have a Duraforce powered LB? Did you ever try rejetting it?

Thanks!
Bill

The DF is an excellent engine, and the carb bashing is overdone. Yes the jetting is lean, but after opening them up a tad, they carbs are as good and reliable as any others.

The idea of the carbs not requiring modding of the jets due to them running good initially or for a period of time prior to the surging, seems logical. However, one has to remember these carbs are literally at the "ragged" edge" of lean with no cushion for any foreign particle, buildup, etc.

While this type of jet size selection may meet ever encroaching and arbitrary EPA requirements, as well as performing satisfactory in a laboratory setting, they do not perform reliably in the real world.

That is why the re-jetting works as more of a permanent fix. Technically, one should be able to thoroughly clean the stock carb/jets and the unit should run as it did when new. But even if successful, the longevity does not exixt and the procedure will have to be repeated occasionally.

...make that "satisfactorily". Dang no-edit feature!