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I have a pretty good idea of what I'm going to do. However this is the first time, and any thoughts, tips, or advise would be appreciated. I can't wait for this mower to run at it's potential. Thanks.

So WHY are you wanting to richen the fuel mixture...
Do you think it is Under carbureted? :smile:KennyV

I believe the mixture is too lean. the mower surges terribly at idle and the mower has a VERY slight surge at high idle, almost unnoticeable. I want to smell the exhaust. I want it to run like my older ones. These mowers were lean from the factory for EPA approval. I have read a little about driling the jets, but I just wanted a little advise.

I have re jetted V8 engines... all I can tell you is that very Small changes make a lot of difference ...
In a small displacement engine it will be even less change for a Big difference... :smile:KennyV

Yeah, me too. But I have never drilled one out of a lawnmower. I think I'll be OK, but who knows.

KennyV said:

I have re jetted V8 engines... all I can tell you is that very Small changes make a lot of difference ...
In a small displacement engine it will be even less change for a Big difference... :smile:KennyV

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I'll second that.

It will be very hard to properly fine tune a small engine like that -- but maybe I'm wrong. :confused2:

Have you exhausted other possibilities?

I guess you could replace the jet if you drill too much.

I have never understood why any rejet or drilling is necessary on a stock Duraforce to run "right". IMO it is a band-aid for some other problem.

When the mower/engine was new I'm betting it ran perfectly,...right??, just like my first LB 10323.

Then after 8 years of heavy use it started surging a bit. All I did was study up on the carb for these models, rebuilt the original one in complete stock form, replaced all mounting gaskets and torqued carb to engine properly,.....and it ran and continues to run perfectly 6 years later, does not surge one bit at idle or full throttle.

Recently I acquired two Duraforce LBs,....both surging badly and pretty much left for dead. One I rebuilt the carb on,.....runs perfect now. The other I replaced a badly leaking bottom crank seal, runs perfect now. Still others I've had to replace the carb with a new one as usually some ham fisted shade-tree engineer has tried to "improve" upon LBs design,....instant trouble.

IMO these things surge due to a problem, not some flaw in engineering. I've never had to solve a surging problem with re-jetting, just gone by the book, fixed the problem and they tend to run perfectly again.

Good luck with yours.

This mower runs near perfect at high idle. Low idle surging is terrible, (I could just clean it) and I've heard that these were tuned lean to comply with the EPA. I have also heard that these mowers, when disassembled, show signs of lean/hot operation. So...it runs fine when I need it to, and I never run at low idle. I am doing this more for fun and longevity (and learning) and if I fail, I merely buy new jets. Not only that, I want to smell the exhaust.

coolted said:

This mower runs near perfect at high idle. Low idle surging is terrible, (I could just clean it) and I've heard that these were tuned lean to comply with the EPA. I have also heard that these mowers, when disassembled, show signs of lean/hot operation. So...it runs fine when I need it to, and I never run at low idle. I am doing this more for fun and longevity (and learning) and if I fail, I merely buy new jets. Not only that, I want to smell the exhaust.

Click to expand...

The only time a Duraforce may surge will be for 10 or 20 seconds right after a cold startup, after that if all is correct in the engine they should not surge at any speed idle through full throttle,....with all stock components. Now this does not take into account bad gas, etc.

I'm sure Lawn-Boy designed the Duraforce to be as clean as possible in regards to the EPA, but they would not (and did not) produce a surging mess when new. Every Duraforce I have come across that has been maintained properly does not surge, however there is a large majority of hacked up messes out there.

What is the history of the mower? Has the carb been rebuilt properly and setup to spec? Many people dismantle the carb to try and fix a problem and don't have a clue what they are doing. The needle seat, idle and main jet along with main jet nozzle need to be inspected and cleaned or replaced if necessary, then sealed and torqued correctly. Is the float set at the correct height? How are the two gaskets between the carb/heat shield/crankcase? Does the airvane shaft show any signs of wear and fit loose? Any problems here = surge city. Any signs of leakage from the top or bottom crank seal will be a problem also.

Moral of the story: True, they do surge due to lean conditions, but this is not due to jet sizing, but other air leaks and improper setup that cause the condition.

Well...I drilled the jets...fixed the low idle surge, and it purrs like a kitten at idle. However, high idle is a mess. Runs EXACTLY like a 10227 that I can't figure out. I find this interesting, as I didn't think that the 10227 had ever been modified. The 10227 has new reed and seals, needle and seat, and float. Hmmmmm.... this is where the learning begins.

UPDATE>>>

Ok...So...I put the stock 77.5 jet back in, left the pilot drilled to .015...Still not acceptable, but better. Mowed a big pile of leaves, and after getting through the pile, the rpm's shot up and stayed there. I determined that the governor spring was bad, and when I took it apart it I saw it was tweaked. I replaced the spring and have a nice high and low idle, and surging is intermittant. When a load is on it, I get the power hum which i love soooo much. Gonna be a long wait for the grass to grow this time of year...I am so close.