Small Engines (Lawn Mowers, etc.): Loss of engine power and backfire, valve clearance, intake valve

Question
Hi Michael,

My problem is that once my 2002Cub Cadet 2146 model warms up I run into a loss of engine power and backfire, intermetent on the 14hp OHV engine. The motor has had a backfire kit put on the carb, by the dealer. The only other thing I can tell you is that if I turn the PTO off sometimes while the problem is happening the motor will run ok. Other times when the problem occures I turn motor off and it let set of minumim of 10min., and won't have the problem for the rest of the day. The battery is new as of May 2004 so I am certain it isn't due to bad battery. I have checked for loose grounds and cannot find any loose. Maybe coil, and how do you test if that is the most likly cause?

Thanks for your time and advise.

Jim  

Answer
Hi Jim,

Sometimes a coil will fail or become weak when hot but that shouldn't produce backfiring.  I suspect the backfiring is due to insufficiant valve clearance, causing the intake valve to not close completely.  Why it is intermittant, is a mystery, unless the valve sticks sometime.

Let me know how you make out.
Michael