This is on my ZTR. 350 hours on it. Runs fine....until you get it good and hot...then turn it off. When you restart the engine it runs very rough with a noticeable drop in power for 2 or 3 minutes then goes back to running fine again. I have replaced the plugs and fuel filter because they needed it anyway. Never seen this before and I'm stumped.
Try turning the choke on while it is acting up to see if that makes it worse or better, that may give you an idea if it is running rich or lean. I was initially thinking there is a fuel delivery issue, but now that I re-read your OP, I'm thinking more so that it could very well be the ignition coil heating up after you shut it down and then when you start back up the engine cooling air flowing around the coil cools it enough to let it fire properly again (assuming this is an air cooled engine...or at least has the coil mounted in an area that gets some forced air cooling) Use your old plugs to check spark on both cylinders (its a twin right?) when you are ready to do a hot re-start, see if maybe one side is cutting out or weak when hot.
Air cooled twin. I bought a 4 pack of plugs because it was cheaper than 2 individually. I'll try that the next time I mow.
A friend's Yamaha Rhino had the same symptoms. He could pour cool water on the vacuum fuel pump and it would straighten right out. A new pump (every year or two) fixed it. You may try that while diagnosing.
I agree, I would ohm check the coil hot and cold, there should be a spec for it if you care to look it up.
I pulled up the IPL and it has dual coils. Sounds like it is running on both cylinders when it acts up...so....I don't know. Fuel pump is $22 and coils are $50 each.
Got a laser thermometer? You can use it to see if you have a cooler cylinder which could lead you to the issue.
Nope. From cold start to first shutdown it runs like a champ. Just the first 2 minutes on a hot start are trouble.
Sounds like both cyls are firing huh? Hmm, well, with dual coils that likely rules out the coils...could still be ignition module or pulse coil (if it even has them) but is sounding more like a fuel issue to me. If you do have a laser therm, shoot both the exhaust pipes as close to the head as possible to see for sure that both are firing. If they are, then try giving it a lil choke to see if it gets worse or better. If it gets better, then it could be anything from a cracked fuel line to some crap floating in the fuel bowl...bad fuel pump is a real possibility too...or a fuel pump vacuum line collapsing when it gets hot...seen that one before.
I see a lot of fuel pumps sold at the exmark dealer as preventative maintenance. 10 times more than coils. That's all the help I have.
Lemme get this straight, all is well as long as you never shut it down? The problem only presents during a hot re-start?
Wierd. Sounds like a vapor lock type situation where the heat soak while shut down is enough to boil fuel in the line, pump or carb but it sorts itself out with airflow from the flywheel fan.
Update. This problem went away for 3 or 4 mowings...then came back with a vengeance last Friday. I hooked up my spark tester on both plugs and they checked out fine. On a whim I decided to pull the carb bowl and noticed one of the vacuum lines had come off....looked like it had been off for a while. Problem persisted so I dropped the bowl and it had lots of sawdust and various nastiness in there. Sprayed it all down with carb cleaner and she's running like new again. I'm guessing it had to run for a while to stir up the crud...dunno? I will probably pull the carb and really clean it up good this winter as there is probably more junk still in there.
Small amounts of water in fuel used to present similarly before the days of ethanol. It would sit their harmlessly in the bottom of the carb bowl until you found a rough patch in the yard and then sputter, sputter, KA-POW, pop pop, and silence.
