1988 Yamaha Warrior loses power when warm

[yamahariders3]

:aargh:I have a 1988 350 Warrior that is not running right. It runs okay for about 15 minutes, but once it heats up, it spits and sputters and losses power. The exhaust gets louder when I lose the power. It has an HMF exhaust. I have tried two different carbs and have adjusted them both and I still get the same thing. No matter how I adjust the carb, it doesn't change. The parking brake is disconnected and all wires are out. I have checked the stator and pick-up and source coil, and they are fine. Stator is only 2 months old. Checked valves and they are okay. Have checked the harness and can't find any cut wires. The timing is good. The air filter is clean, and I have also tried running it with the air filter cover off, and there is no change. I have tried taking the exhaust off and there is no change. Sorry for the long story, but I'am trying to list everything I did to help you figure something out. I just don't know where to go from here and am hoping someone can help me with this. Thanks for any help given.

[RockyMountainATV]

I would say from what you've listed and tried that the cdi is bad or going bad. They are susceptible to heat and seem to act up more once a machine has been running. Other than that you've covered everything I can think of. I guess it could use new rings and possibly a piston if the machine has a lot of miles.

[yamahariders3]

Thanks for your reply. The piston and rings are a year old, but I'll have to do a compression test to check it. Can the CDI go slowly like that? Most people say they just go all of a sudden with no warning. I would hate to buy one and it's still good. Thanks again.

[Stoopidbot1]

I have seen CDI boxes do wierd things. Only allow the bike to rev half way, make the rpm's go up and down. All the way to just stop working. Most of the act up once the box is hot

[Stoopidbot1]

I changed the name of your thread so if someone searches for the same problem they can find it.

[yamahariders3]

Thanks for getting back to me. I'll have to check that. I'll probably be checking the compression in a day or two when I get time.

[yamaha_man95]

well i would try to re-jet it either go a few jet sizes up or down