engine making wierd noises? :S

hey, so i bought a 2004 yz 450 the bike was stock when i got it, so i put a fmf pipe on it and new air intake. the bike was runnning lean the header was glowing red hot jus after a cold start. so i re jetted the bike and the took it for a ride and the bike started making a really loud vibration noise coming from the engine about 45 min into the ride. i cannot figure out what is going on. perhaps the valves need to be done again? the sound to me is a vibration coming from the engine or something slapping on something else.....any sugestions?


Yamaha makes some wierd slapping noises in their four strokes sometimes. I have a Raptor 660 that does that and it is built to the hilt i took it in and they said its normal. Its your valves opening and closing extremely fast. If soemthing happens to it get kibblewhite titanium valves. And since it is a 450 it will be louder than most so dont worry about it.

Search the FAQ with regards to your header. Don't re-jet.

Have it looked at or compare it with a couple of similar bikes to see if the noise is normal or not.

should the header be red hot shortly after start up? only ideling for a minute? ive never had that happen before

and by red hot i mean glowing red. even had like sparks come off the exhaust.

Normal would be red heat, easily visible in twilight, or a garage lit by two 100 watt bulbs after a minute to a minute and a half. Frankly, running too rich is more apt to cause it than too lean. More prone to it with the choke on.

thanks for the input. appreciated. this bike is jus drivin me nuts!! the reason im so paranoid about it is because my last bike 3 times even after yamaha mechanics rebuilt the motor.

its a 2004 yz 450 its all stock except for a k&N air filter and a fmf powerbomb header with a power core exhaust where i live is 76.2 m above sea level. any jetting suggestions would make my life allot easir.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now