27HP kohler loses spark and then comes back for no reason

[Jimma]

I have a vermeer stump grinder that seems very temporamental & can't figure it out. It normally starts right up and after it starts runs all day. But if I shut it down and try to restart it, I have no spark some times. After fiddleing around with it for a while, not really doing anything meaningful, it magically comes back to life. I've cleaned every terminal and plug readjusted the coils, checked everything I can think of. It does have an oil sensor, but I thought that the power would completely cut out if that tripped. The machine still turns over when this is happening. There is one part in the book that is not identied but appears to be some type of relay attached to the carb. Anyone got any idieas?

 

[blades]

What you are referring to on the carb is a fuel shut off solenoid. Your main problem sounds an awful lot like the coil heating up and going open then cooling off and reconnecting. Same thing can happen to solid state ignition modules as well. When its running there is enough air flow to prevent , when you shut off it becomes heat soaked and your problem appears. Some of those low oil sensors can be quite finicky as well and the dip sticks on most units are not particularly well calibrated to each particular engine. Oil sensor will not prevent turning over but will give fits starting and or run for just a bit and then shut it down almost like a blocked fuel line/ fuel filter or blocked fuel tank vent.

 

[Jimma]

Thanks for replying brother. I also thought it might be the coils but not sure how to check them. But I'm glad you replied and motivated me to pursue that. Thanks

 

[MTNBOY]

yeah i would lean towards coils also.

 

[Jimma]

I was just thinking about the coils and I remembered that the flywheel fan is a bit beat up and has a couple of fins broken. I'm wondering if that is what cools the coils when it runs and the fact that it may not be cooking it as well as it should might cause the coils to heat up.

 

[MTNBOY]

could be an issue. but if its not dieing while its running that would assume it cools the coil well enough. its the after shutdown heat increase that might be just putting it over the edge. the constant cranking afterword could be enough to cool it down. try maybe just cooling off the coil or try another? small homemade heat shield between the block and coil?

 

[Jimma]

When I say coil, I'm referring to the ignition modules that get spark from the magneto on the flywheel. There are actually 2 coils and they are pretty expensive, about $100 each, so I'm trying to elliminate everything else before I spend the $200. Now I'm having doubts because I couldn't get a spark from a cold start the other day until I fi=ddled around for a while then it came back to life. But normally it was as I said. Start right up then if I shut down the spark would disappear then suddenly come back on later.

 

[MTNBOY]

yeah makes sence. possibly can get one to test? have another unit you can pull it off.

 

[MTNBOY]

are you getting juice between the magneto and the coil packs?

 

[Jimma]

How would I test that if it's not going beyond the coil? Funny thing is, I just sold another grinder the exact same model and a brand new engine that I had for it. Never had a bit of trouble when I had the two machines and the extra engine.
As you can tell, I'm not a mechanic, but by necessity, need to do my own repairs. I appreciate all the assistance, thanks

 

[MTNBOY]

kinda tough to say without seeing it. im no real mechanic just can dabble in most stuff. possibly check all wires and connections also. maybe get ahold of the guy you sold it to and see if you can borrow one to test off the old or new motor?