18 hp kohler

[jmart045]

Motor will start and run but backfires and won't idle also does not want to go in high gear bogs down. What could this be? Just cleaned carb and new plugs any ideals?

[North Country Tough]

Motor will start and run but backfires and won't idle also does not want to go in high gear bogs down. What could this be? Just cleaned carb and new plugs any ideals?

Replace the ignition coil.N.C.T

[JohnF]

Don't really know the answer for you but:

Is it a backfire or afterfire? Backfire will shoot flames out the carb and generally indicate something wrong in the timing - like you have an open intake valve at the point of ignition, or hot spots in the cylinders (like maybe from running lean) that ignite the fuel mixture before the valves close.
Afterfire is raw fuel/air getting dumped through the exhaust and igniting off of a hot spot in the muffler.

If backfire I would first guess running too lean if afterfire I would look into ignition.

Next: Did it have this symptom before the carb rebuild and before the new plugs or is this new since then?

I don't know this engine at all but my first inclination would be to follow NCT's advice and test that you are getting spark. One way is to take another spark plug and for each cylinder (while engine off) pull the plug wire and attach to extra plug, lay plug on engine so as to ground it, crank engine to see if you see (or hear) a spark. Another way, and a favorite of a farmer local to the family ranch, is to take your pliers and pull the plug wire while the engine is running and watch for sparks to jump from your belly to the vehicle. I think that one hurts but that guy thinks it's funny.

[Joe H]

Check your fuel pump and the pulse line and fuel filter, the ethanol in gasoline is hard on fuel systems.Doesn't sound like ignition to me, even with a weak spark it should idle at least roughly and act up when you try to give it throttle.