Small Engines (Lawn Mowers, etc.): plug fouling, piston rings, plug gap

Question
David,

I have a exmark ztr with over 1000 hours on motor. Was burning oil and had small leak. The final straw was that it started fouling out the plug oh head 1.  I replaced the short block but still had fouling.  I then replaced both heads (and at this point wishing i had replaced the whole engine) Unfortunately it is still fouling out the same plug.  After about 30 minutes it gets so much carbon build up it will not fire and I have to stop and clean the plug or put in a new on. The only thing not replaced on this engien is the carb and coils.  Any advice?

Thanks,

Jason

Answer
Jason,

   the fouling is being caused because your engine is not keeping the oil in the block where it belongs
since both heads were replaced and the plug continues to foul out it appears that the Piston rings may be failing
the Carb does not have enough oil in it to cause your plug to foul out and if your using clean fresh gasoline there is no chance of the fuel laqcuering out
Try this
take the Spark Plug out clean it and close the plug gap see if that helps if not open it up a bit more what your wanting to do is increase the amount of spark heat in the engine run it  for 30 mins and pull the plug take a look if the carbon stops building up then thats  the gap you will want to use.
But By all means inspect your Piston rings for wear if when you rotate your engine and the piston travels down and you see excess oil on the cylinder sleeve walls then you Know your rings are worn and will need replacing Increasing the Spark heat will burn the excess Carbon out of the head
Step 1 Inspect the Piston rings
Step 2 increase Plug heat
Note only increase plug heat if you dont see wear on the rings