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engine backfires

#1

B

BRIAN10

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?


#2

M

mechanic mark

Before shutting engine down allow 30 seconds run time at idle.


#3

B

BRIAN10

mark thank you for your help... will check it out...


#4

tom3

tom3

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.


#5

Hammermechanicman

Hammermechanicman

BRIAN10 said:
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 ..

. but if you put about 1/3 choke on it runs very well ...
Click to expand...
Sounds like it is running lean. I would clean the carb and go from there.


#6

B

BRIAN10

Hammermechanicman said:
Sounds like it is running lean. I would clean the carb and go from there

hammer and tom... thank you for your help... my dad did say he thought it was surging a little too.. someone send me an email said it could be the jet behind the solenoid at the bottom of the carb .. I do have a temp gun and will check it out..
Click to expand...


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