cos in alaska
New member
I picked up a used 03 Viper Mountain with 352 miles on it. I ran it a little 2 weeks ago and it seemed to run fine. Now tonight (colder temps) at -5 F, it started fine. I used full joke, waited for it to labor a bit and fliped the choke off. I went to another machine and started it. The viper had died. I had to use a little throttle to get her started. It acted is though it flooded out. I stayed there and baby sat it with throttle and choke untill the snow was melting on the boards. I then went around the yard once. It wasn't firing on all 3. It died and wouldn't start agian. Yep you guessed it. I fouled the plugs.
Bad thing is the center plug was bone white and dry. the outer where carboned up and wet. I noticed I could see tiny clean areas on the top of the center cylinder. the outer two was good and carboned up. I put in three fresh plugs took a spin around the yard. Now it will not idle and when the RPMs drop below 1000 the power valve actuator cycles and the engine dies shotly after. Again the center plug looks as though it is running to lean.
A Little background: The previous ower ensured me it was jetted for sea-level and -10 to 20 temps. He and I have been running Yamahas for years. I on the otherhand am new to power valves. I have not removed the airbox or checked carb adjustment.
Q: Should the power valves actuator be acting this way? Could there be a hose off or incorrectly routed on the center carb?
Bad thing is the center plug was bone white and dry. the outer where carboned up and wet. I noticed I could see tiny clean areas on the top of the center cylinder. the outer two was good and carboned up. I put in three fresh plugs took a spin around the yard. Now it will not idle and when the RPMs drop below 1000 the power valve actuator cycles and the engine dies shotly after. Again the center plug looks as though it is running to lean.
A Little background: The previous ower ensured me it was jetted for sea-level and -10 to 20 temps. He and I have been running Yamahas for years. I on the otherhand am new to power valves. I have not removed the airbox or checked carb adjustment.
Q: Should the power valves actuator be acting this way? Could there be a hose off or incorrectly routed on the center carb?
yamaholic22
Active member
I think your problem is a plugged pilot jet in the center carb. You're gonna have to get those carbs off there, pull the float bowls and clean the jets. There are how to instructions on the tech pages if you don't know how to do that. The powervalves should cycle when it gets below 900 rpm, so you're good there. Any other questions just ask or PM me. 
What holic said, if you just replug it and try again, you may need a piston. maxdlx