Dang So Close! - FOLLOW UP.

.....I have been dialing in my yzf450 for months. I finally got it super sweet.

8oz flywheel

47 rear

WB Carbon Pro Exhaust

Azonic Bars CR HIGH

Pro Circuit Susp.

The thing glides a round the track, and the power is super sweet-:)-.

.....But I can't get rid if it decel-back firing. I hear other guys around the track having a little bit of it, but mine does it a lot. It also acts like there's an air leak somewhere. When I am comming back into the pits, it idles high until I snap the throttle a little.

.....My track buddie who I carpool to the races with, laughs at me. He rides a Honda 450 and just bags on my Yami. In good taste, he kindly mentions how his doesn't back fire or idle up. I gotta get this figured out. You know when you are super confident in your machine, you're that much faster.

.....Thanks in advance guys, Any info or suggestions would be greatly appreciated.


You say it idles high until you snap the throttle. I can think of 3 possible things that would cause that. An air leak somewhere (check your air boots), lean pilot circuit in general (turn the fuel screw out a little), or your throttle cable is too tight or hanging up somewhere and holding the throttle open a tad. Maybe someone else has better ideas, hope this helps.

decel backfiring means it could be running lean. You mentioned nothing about adjusting your fuel screw. I would start there. The fuel screw running lean also makes the bike idle high.

.....I haven't touched anything on the carb. I had heard that backing the fuel screw out a little does take care of the backfiring etc. I know for sure that the cable is free and not hanging up.

.....I am going to thouroughly inspect the air boot, and make sure it's not cracked or leaking.

.....Exactly which one is the fuel screw, and how much should I be backing it out?

Again, THANKS!!


The fuel screw is accessed from the bottom of the carb. Unless Yamaha changed the fuel screw design, you will need a very short screwdriver to squeeze in between the engine and the float bowl.

There are replacement fuel screws available that stick out enough where you can turn them by hand, even while sitting on the bike!!

Since you have never touched the fuel screw, this could VERY EASILY be your problem.

Never having touched it before, you may have a slightly difficult time even seeing it. You can use either a mirror, or rotate the carb to figure out where it is.

Be sure your carb is in it's normal position if you light off the bike.

.....Thanks bro. Even though it's snowing I went into my garage, Brrr! I dug out the manual (great idea huh?) and located it. It was a hair shy of 2 turns out. I went 2.5 as the manual recomends 1/2 turn increments. If it's too fat I'll go back 1/4 turn.

I'll ride it again tomorrow hopefully. Thanks guys.

Snow and so cal don't mix.


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