I have a garage kept 1995 Toro w/b with a 14Hp Kohler that has run flawlessly for 6 years......amazing what clean oil,filters, and some preventative maintenance will do.....
Just recently it will run fine for a while and then begin missfiring and sputtering (maybe every 2nd or 3rd lawn I maintain) at which time I disengage the mower blades and reduce the throttle to try and eliminate another tug on the ole pull start. Sometimes it will recover and others it will just stop. When it stops it will not start. A 10-15 minute rest and it usually (not every time) fires right back up. I do not want to take it into the shop and have it run fine for them and waste a shop charge. Only if you spend an entire day on the mower will you get a feel for it. (best decribed, very unpredictable) I don't feel as though its a fuel problem (other than being a $1.61/gal for 87 octane.) It's almost as though something may be heating up to cause the failure.
I've read the threads of a similar problem happening on a 12Hp Kawasaki and many responses were leaning towards replacing a module of some kind.
I've replaced the air filter,spark plug(ChampionRC 12YC @ 0.035" gap), fuel filter,(removed and cleaned fuel tank too) fuel line looked good, pulled the carb and sprayed every orfice possible w/ carb. cleaner. Right before any problems occurred, while performing a good cleaning of the cooling fins I do remember cleaning oxidation off the ignition coil and flywheel magnets with some fine sandpaper. In my manual there are 3 items labled module.(ignition coil part #12-584-02, located under the T-Bar is an interlock module part #82-3850 & another under the T-Bar part # 86-7910) Which one? I'm mechanically inclined until MODULE....huh?
Many Thanks for your input!