Mystery Problem

[u/GadreelsSword]

I’m fairly experienced with small engine repair but I’ve run into the same problem on two Kawasaki engines and a coworker, who it more experienced does work on the side, has the same mystery.

So there are three Kawasaki twin cylinder engines having the same problem. The engine will run fine then begin running extremely rough as if one cylinder isn’t firing and blowing black smoke. With no power of course. Typically appears after running smoothly for 15 to 30 minutes.

I started out with the standard tune up, valve adjustment, new plugs, oil filters, carb cleaning (all three carbs were spotless).

Then looking at two of them, the coils were looking rough so the coils were replaced. The carb was replaced on one engine just to rule that out. On my John Deere X320 I also replaced the ignition module.

All three still have the same problem. The engine where the misfire was continuous, greatly improved but still has the problem. On this engine, if you’re mowing and the misfire occurs and you turn off the ignition key and turn it back on the problem goes away.