2005 yfz 450 problem


Hey, so I am looking to get my buddies yfz 450, Its a 2005 and it runs, but when you get past the 1st quarter throttle or so, it starts blowing smoke and bogs down. It doesn't die, but it has no power. Just wondering if anyone knows what's wrong and if it's a cheap fix or not. I think it may be the jetting on it or possible piston rings are bad and letting oil in to the combustion chamber. Anything helps. Thanks.

Blue/white smoke means it's burning oil. Either valve seals or piston rings. If it's black smoke that is a rich condition, and needs rejetting


Hey thanks for the quick response. It is blowing white smoke with a blue-ish tint, so I guess I am going to get my hands dirty doing some top end rebuilding! Thanks again.

Hey I'm back with more questions! Never redid the top end, but a bolt was missing from cam cover. Got new one in, new spark plug, and found out the starter relay is bad. When I bypass the starter relay, it just sits and cranks but won't start. It has spark, it's getting fuel, and every once in a while it backfires. Wondering what may be wrong now, if anyone has any ideas? Also tried pulling it behind vehicle to see if it would start but it just backfired like a gun shot a bunch. If anyone has any ideas, it would be really great, kinds pulling my hair out about now

Definitely test compression, clean out your carburetor, make sure it's all at factory specs. My best guess is that your oil ring (piston ring) was gone, letting the oil through, and one of your compression rings went, however I can't see it in person.

Ok, I cleaned the carb and all, but it still is doing the same thing, only backfiring more often when trying to start. What I don't understand is if the piston rings are bad, how does that make it backfire when you try to start it? It was running 3 to 4 weeks ago. The jets are a 140 main and 90 for the other. Are these right?

Ok, looked at timing again, and it was off. So I redid timing and now when I start it, turns over real slow. Help please! Doesn't backfire though, which is good

Take out the spark plug and see if it turns over any faster, adjust valves, double check timing, and timing chain tension.

Edited by 110Tim

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