L100 stumpling issue

AuCivil · Aug 8, 2015

Bought an old L100 with Kohler CV491s engine. Cranks fine and runs good for the first few laps (only did one when test driving). Then the engine starts stumbling. Still running and able to cut but it feels like ever lap is bound to be the last. Also has a nice backfire at the end when you shut it off.

I have cleaned the tank, blown out line from filter to tank, replaced fuel filter, replaced air filter, replaced spark plug and also tried running it without the gas cap.

Any ideas?

jenkinsph · Aug 8, 2015

I would check the compression with a gauge after the engine is warmed up. If compression is good I would consider checking the ignition coil next. I would also pull the spark plug to see how it looks after it starts stumbling as you say.

AuCivil · Aug 8, 2015

jenkinsph said:
I would check the compression with a gauge after the engine is warmed up. If compression is good I would consider checking the ignition coil next. I would also pull the spark plug to see how it looks after it starts stumbling as you say.

The stumbling is somewhat like a miss but not at regular intervals somewhat like running out of gas.

Motor doesn't smoke and the plug was black. Don't have a compression gauge but can probably find one.

Also noticed there didn't seem to be much fuel in the filter while it was running.

Gary Fowler · Aug 8, 2015

I wouldn't worry about air trapped in the fuel filter if it is laying sort of horizontal, most fuel filters leave an air bubble in them. As long as it is full past the entrance and exit, it is flowing ok. I also would suspect the ignition coil as the culprit as many of them go bad when they get hot but work fine cold.

AuCivil · Aug 8, 2015

Gary Fowler said:
I wouldn't worry about air trapped in the fuel filter if it is laying sort of horizontal, most fuel filters leave an air bubble in them. As long as it is full past the entrance and exit, it is flowing ok.

The fuel filter is clear, about 45 degree angle and has just a small amount of fuel visible while running.

RandyT · Aug 8, 2015

Black carbon that wipes off on the plug indicated rich running. make sure the choke is opening all the way. Sounds like it could be going rich after warming up. Also when you shut it off move the throttle to 3/4 to full to avoid the afterfire. just the way Kohler carbs are set up with the fuel afterfire solenoid.

jenkinsph · Aug 9, 2015

I would not worry about the fuel filter with air trapped in it either. That seems to be a normal occurrence.

Years ago I installed a small metal inline filter and a small electric fuel pump hooked to the ignition circuit. Works great and reduces cranking the engine to a quick bump of the starter.

I would suspect your problem isn't fuel to the carb. since it starts up okay and runs good till it warms up. How long have you run the mower under load when this problem occurs? Randy makes a good point about the choke, make sure it is opening up fully before proceeding. With the motor warmed up and engine oil hot I would check the compression first as this is easy to do. If it is good I would then look at the ignition coil as the culprit.

Others such as Randy can provide you with better information about the coil testing and replacement than I can.

AuCivil · Aug 9, 2015

jenkinsph said:
How long have you run the mower under load when this problem occurs?

Maybe 10-15 min.

AuCivil · Aug 22, 2015

So I made it back to the mower and was prepared to do a bit more testing and I discovered a new, more serious symptom. I had left it parked on a slight incline with the front pointed downhill. Raised the hood to check the choke and make sure it was operational. Noticed a little liquid had dripped out of the shield around the muffler. Checked and it was clean engine oil. Thought something may have been oiled too much and proceeded to check the choke. Was initially stuck but got it operating freely.

Proceeded to crank the engine. Engine fired up and oil shot across the patio and the engine died. Just for sh@#$-and-giggles I gave it another try. More black oil shot across the patio, the engine stumbled around and died. Black oil was pouring out of the shield around the muffler.

Ideas?

Guy that sold me this mower got me good.