I am working on a 2000 Warrior for a buddy. When he brought it to me the main problem was the common parking brake switch problem. I unplugged it and you can actually ride it now but it runs like crap. At Idle and low rpm it seems ok, but if you try to get in the throttle even halfway quickly it stalls and dies unless you pull in the clutch and let off the gas. Even in neutral if you stab the throttle to halfway it will stall. If you ease into it you can ride it but it doesn't run very well.

It has a brand new carb on it that was purchased new from Yamaha by the owner, but I disassembled it and made sure all jets and passages were clear just to be sure. I didn't find any obstructions in any of the passages. I have inspected the carb boot and found no problems there. No problems with the air filter either. Valve timing is right and I adjusted the clearances. All ignition electrical components check good with a meter and spark looks great outside the cylinder.

Trying to think...I have checked it out pretty thoroughly, but is there something I am missing. The muffler (silencer) is basically just a shell, no baffle or guts. Could this cause such a serious decrease in performance? Personally, I'm wondering if a valve is slightly bent and not closing all the way. If a valve was bent, even just a little, would it cause contact with the piston? I'm not seeing evidence of that.

Any input would be helpful. Thanks

 

I know you cleaned the carb already, but it sounds like the main jet is plugged, or it's starved for fuel because of improper float height. Or is the main jet the proper size?

In my experiences with Warriors, a hollowed muffler decreases performance, but it's across the whole powerband, not just at full throttle. It wouldn't make the engine die, just mmore sluggish.

If the valves were hitting the piston, that would be major and the engine probably wouldn't run. I've had that happen to a Warrior I had and it was not good! If the valves were bent just a little, it wouldn't have much compression, if any. You could do a compression test to eliminate that problem.

 

Your carb might just need tuned right. Ive heard of bad stators doing this too

 

Thanks for the input guys. I got the bike going yesterday simply by raising the jet needle. Sometimes it is easy to overlook the obvious things even though it shouldn't be.

When I got the quad to work on, someone had already attempted to work on it. Standard bolts were threaded in some of the holes and the intake valve was grossly out of adjustment, among other things. The owner had already purchased and installed a brand new carb from Yamaha.

Anyway, yesterday I started by making sure it had the right jets in it, 145 main and 42.5 pilot, which it did. I knew the passages were clear so I tried running it with the choke on after the engine warmed up and my problems disappeared. Then I raised the needle and it took off like a champ and the missing was gone. I rode it for a little bit to make sure it was going to be ok and it ran fine. Personally, I feel like an idiot for not checking that sooner.