I have a 90 9.9 4 stroke Yamaha that I use as a kicker motor. Over the last 1 1/2 years it has been running intermittently.

- the motor will initially run great at trolling speed.
- after running approx. 10-20 minutes it begins to miss. When I slow down to an idle speed it sounds and runs fine - when I speed up it runs rough and sounds like it's running on one cylinder while continuing to miss.
- after fussing for 5 to 10 minutes it catches and will run correct the rest of the day at all speeds

Any ideas? I've taken it in to my usual place a few times for repair. Each time being told it's fixed when it isn't. The fuel filters are changed annually (sometimes twice), tune-up every year, etc.

Thanks for your help!

Salmonnut, just went through this on a 89 9.9 yamaha, identical symptoms, trace the kill switch wire haeness down to the cylinder head and unplug (i believe its white) wire should be a plastic cover you need to remove first, and see if it runs fine, have had a couple incedents both times its been wireing, one other guy had a similar missing problem and it to was wireing, good luck Doug

I have a used mid 90's Yamaha 9.9 electric start and went through something similar. Mine had to have the head gasket replaced and a new thermostat. Now, idles down fine and runs like a champ. If you haven't tried them, I would recommend giving Sandy's boat house in Everett a call. If nothing else, you can buy the parts you need from them and try it yourself. I have also started faithfully running the bowl dry after flushing.

Sometimes the auto choke will stick

I have to reply with the same thing every time I hear of any engine running for 15 min then going to crap....make sure your not getting back pressure from your gas tank. it it builds up pressure, the engine well start to sputter...DJ

Thanks for the tips. I'll give them a try! I'm thinking it's the wiring because the kill button doesn't work either, I'm having to pull the emergency shutoff plug to turn the engine off. Of course...this was one of those things that was supposedly fixed!