I have a 99' warrior. Got it from a friend and rode great. Now it starts fine, but when I give it gas it continuously backfires. It even sometimes backfires in choke. But if I give it too much gas, it backfires than shuts off. I do not know what the problem is but checked air filter and tried cleaning the carb. The carb seems clean and I even bought a new main jet. Before this happened my brother added some motorcycle oil. I dont think that would mess it up. Any thing will help me right now.

 

did this happen out of nowhere? or did you do something (besides adding oil) and then have it start to happen? what mods and jets are in it?
maybe an air leak? spray carb cleaner around the intake manifold and the intake boot while its idling and if the rpm's jump you have a leak. check to see if the carb is hooked up correctly to the boot and intake manifold. and check the manifold for cracks. backfiring usually means it running lean for some reason. if it runs any better with the choke on, you know that its runnig lean for one reason or another.

 

parking brake?

 

yeah is the parking brake assembly/wires still on the bike? theres a rev limiter that causes all sorts of problems on the yamahas when the parking brake assembly/wire switches gets dirty and what not. if its on there, take it off and take off the wires that go to the clutch perch. if you need more explanation, just ask its a very common problem with the yamahas

 

Nevermind fixed it, but thanks for the information. It was the parking brake. Would have never guessed! Now I got to adjust it.