YZ450 won't start after rebuild...

[Lowdownbooty]

Hey guys,

I have a 04 YZ450 that i bought used about a year ago. It appears to be stock except for the flywheel.

I lost 4th gear a few weekends ago so I put my limited skills and tools to work tearing the engine down. There were a few hickups here and there but over all the job was fairly straight forward.

Now i have the engine back in the bike all it does is backfire every 15-20 kicks:thumbsdn:. I've checked the cam timing according to the service manual, I'm getting fuel, and I have spark. Is there a chance the timeing is off 180 degrees?

Help!! I have Friday off and I NEED to ride!

Thanks in advance,

jEFF

[Indy_WR450]

Most likely your valve timing is off. It is a good sign that you are getting some backfiring. Recheck you valve clearances and timing.

[Lowdownbooty]

I am supposed to use the "I" on the flywheel correct?

[Indy_WR450]

"I" on the flywheel window and check the cam sprocket punch marks to be at the top of the head casting and the exhaust cam lobe pointing to 9:00 and the intake cam lobe pointing to 3:00.

[Lowdownbooty]

Indy,

Thanks for the responses. It was the shim under the rhight hand intake valve bucket. It was out of its prech keeping the intake slightly open. It fired on the first kick! That is if you don't count the first 200-300 before that....

Thanks again,

jEFF

[Fullbore4]

Indy,

Thanks for the responses. It was the shim under the rhight hand intake valve bucket. It was out of its prech keeping the intake slightly open. It fired on the first kick! That is if you don't count the first 200-300 before that....

Thanks again,

jEFF

Yamaha has sent out a bulletin to dealers on that exact thing. Shims get cocked under the bucket.

[Indy_WR450]

Yamaha has sent out a bulletin to dealers on that exact thing. Shims get cocked under the bucket.

Good find! Got to Love our TT forum. Great knowledge database!

[Kevin_S]

Same shim thing happened on my YZ450 2 years ago. It cost me hours !!!!!!!