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Curtis B.
Curtis B., Technician
Category: Small Engine
Satisfied Customers: 12172
Experience:  have worked on and around most engine models for 35 yrs./Polaris ATV expert
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I have a Koehler 25 hp. motor, it start and runs great, for

Customer Question

I have a Koehler 25 hp. motor, it start and runs great, for the first 10+ minutes, the left cylinder cuts out, leaving the right cylinder running smooth as silk. After about 10-15 mins. the left cylinder will kick in again and runs great. While the left cylinder is not firing the exhaust fumes smells like rotten eggs. This will continue randomly the entire time I am running the engine. Have replaced plugs, air, and gas filters. Puzzles me what to try next.
Submitted: 5 months ago.
Category: Small Engine
Expert:  JohnF2015 replied 5 months ago.
HI, my name is***** will be assisting you.It sounds like you have a bad ignition coil on the left cylinder. I have seen this happen a lot where the coil will only fire intermittently. There are two igntion coils on this engine, one for each cylinder. I normally would recommend that you replace both coils when making a repair, it is easier to replace both at the same time than it is to tear the engine apart a second time to replace the other ignition coil. If you have a good gap style spark tester you could put it inline between the plug wire and spark plug and start the engine and watch to see what the spark is doing when the engine is acting up or not running correctly.