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Discussion Starter · #1 ·
Having a strange problem with a Lawnboy 10525 Duraforce.

:) Runs great with full throttle -minor surging but not excessive, tons of power and surging completely vanishes under heavy load (mulching thick wet 6" grass).

:) Three pumps on primer and a quick pull and starts every time BUT only if left on full throttle.

:eek: However, when you try throttling it back to slow - stalls immediately. If you try starting with the throttle in the choke position, won't start.

:confused: Any ideas?
 

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Definitely sounds like a fuel passage issue. First off, you might try some fuel line cleaner, such as SeaFoam. Very good product. Also, removing the carb and cleaning it would help out. On the side of the carb there is a jet, usually covered by a black piece of tape with numbers on it. That can be screwed out carefully, cleaned with spray cleaner and a very fine wire, and replaced. Might take care of the issue that easily. Let us know.
 

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I have found the info on rejetting the duraforce carb in this forum very helpful. I have followed these exact steps on a duraforce that was having a surging problem and it fixed it. The machine runs like a champ, runs a little richer. But I would rather it run rich and foul a plug than run lean and burn up a piston, rings and/or cylinder. This may fix your problem. It is a known problem on the duraforces to have carb problems. The problem is that because of EPA regs when this engine was made, the jets are set lean. They are a non-adjustable jet, so you either have to clean them well or drill them out as stated in this forum that I found about 3 or 4 years ago.

Duraforce Re-jetting Instructions Part 2 - Lawn Mowers Forum - GardenWeb
 

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Discussion Starter · #4 ·
Carb Overhauled - So Far, So Good

I had planned to replace the jets at some point - but as he mower wasn't surging much under full throttle hadn't done it yet.

Took the carb off, and did the following:
  1. Cleaned Carb and Area Around Carb with Carb Cleaner
  2. Replaced Pilot Jet - Briggs & Stratton 42.5 Jet (801308)
  3. Replaced Throttle Plate - Lawn Boy 98-7047
  4. Replaced Internal Fuel Filter (in carb) with Lawn Boy 94-5787
  5. Replaced gas line adding in-line fuel filter and right angle shutoff
  6. Replaced Spark Plug (old one didn't look to be in too bad a shape but replaced anyway)
Once all together and running I adjusted the speed control vane till engine was running @ about 3500 RPM full throttle (clockwise to increase rpm- counter clock to decrease) which gave about 2400 RPM at minimum throttle.

NOTE: Not sure if I needed to as could see no sign of locking compound on the threads when I undid them but I applied a little locktite thread compound to the threads when assembling to avoid them coming loose with motor vibration.

With how cheap they are I replaced the gaskets at the same time. All the parts together cost about $20. Parts List included:
  • Briggs&Stratton .425mm Jet (801308)
  • Lawn Boy Throttle Plate (98-7047)
  • Lawn Boy Fuel Filter (94-5787)
  • Lawn Boy Float Gasket (98-1362)
  • Lawn Boy Air Filter Gasket (95-7613)
  • 2 x Lawn Boy Intake Gasket (94-5795)
  • Generic Inline Fuel Filter
  • Generic Right Angle Shutoff
  • Champion Plug (CJ8Y)
Haven't given it a workout yet - but running on the bench now runs on slow and fast with surging almost gone (very slight on low throttle and cold). Only problem is that it races when first started if given more than two shots of the primer.

Will report back once it has had a workout.
 

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Sounds like you got a runner now. Once you have the EPA stuff bypasses, they are a great mower. They are a great mow with the EPA stuff, just once the jets get plugged up, well you know.
 
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