Small Engines (Lawn Mowers, etc.): Kohler engine misfires when warm, speed nozzle, time gas

Question
I have a Troy-Bilt Horse with a 7hp Kohler engine Model K161T, Spec # 281271J, serial#10021536 circa 1981. Starts and runs well until it gets warmed up then starts skipping under power. If I set it to idle, it smooths out and runs fine but as soon as I give it more gas it starts skipping badly. I can slow it down to idle, put it in gear, and it will move without hesitation or threat of stalling. Motor doesn't stall at all; just runs poorly until slowed to idle. I used it today for 30 minutes before it acted up. It cools down and runs fine until it warms up again. Had it serviced twice; they replaced plug, points, condenser each time. Gas is fresh. Dealer said it may be the coil but he hasn't tried to replace it; I don't know why not unless he doesn't have one or know how to do it. Any ideas? Thanks for your help. Tom R.

Answer
I have to agree with the dealer.  Have him install an inline ignition tester which will quickly diagnose if it is an ignition problem or not. Sometimes coils get erratic when they are warm.

You don't have a bad kill wire that is touching when you begin to till do you?  (tiller is actually shutting itself on and off) an inline ignition tester will also help diagnose this.  

After you rule out a bad ignition i would be thinking carburation.  Have you had your carb cleaned recently? The symptoms you describe could be due to a dirty inlet needle and high speed nozzle as well.

Is your gas cap venting properly?  

These are my ideas....

China Dave