my dads has a toro zero turn mower with a kohler ch 25 68543 motor.. it has a very erratic backfire can be at lower or high speed .. sometimes very low backfire.. sometimes very loud... the ignition coils were both replaced last year... but if you put about 1/3 choke on it runs very well ... any help would be greatly appreciated... fuel pump? carb?
engine backfires
- Thread starter BRIAN10
- Start date
mechanic mark
Lawn Pro
Before shutting engine down allow 30 seconds run time at idle.
Last edited:
tom3
Lawn Addict
This sounds like maybe one of two things, unburned fuel build up in the exhaust - one cylinder is dragging the other. The choke adds fuel to the weak cylinder. Check temperature at exhaust outlet on each cylinder to compare. Or (two) a small exhaust leak at the head on one cylinder, possible head gasket leak, letting fresh air into the exhaust and getting a reburn of the exhaust. Listen real close for a leak. A nurse's stethescope or just a piece of hose works good for this.
I was thinking a valve a bit too tight but this motor has hydraulic lifters so that's probably not the case.
I was thinking a valve a bit too tight but this motor has hydraulic lifters so that's probably not the case.
Hammermechanicman
Lawn Addict
Sounds like it is running lean. I would clean the carb and go from there.