2008 YZ450F will not idle

Here is my dilemma. I have a stock 08 YZ 450f and it will not idle or stay running unless the throttle is given gas. I have messed with the idle screw and fuel, but this does not help to set the proper idle for the bike. It seems like the idle screw does nothing to help when I turn it or out. However the fuel screw does change the running of the bike, but not the idle. The fuel screw setting is currently set at 2 3/8.

I have reviewed the below link to make sure my jetting spec are correct, which they are. I even purchased the R & D Fuel per the August 08 MXA Mag and this has not helped. The carburetor has been ripped apart a number of times and cleaned to insure that nothing is clogging the jet’s etc. The gas in the tank has been drained and replace as well.

2008-09 YZ450F User Jetting Database


Can anyone help me out?


throttle cable?

What about the throttle cable?

is the hot start plunger stuck?

Nope...the hot start plunger is stuck, I can move in or out.

It sounds like a classic clogged pilot jet to me, Makes sure the jet AND the passage are clear, There is something restricting the pilot circuit.


Like I said I have cleaned the carb, but will rip it apart again to make sure that nothing is restricting the jet and passage..


The idle speed screw, specifically the threaded end of it, must contact the throttle linkage to hold it open. As obvious as that probably is, you might want to remove the linkage cover from the carb and have a look.

Ok, I clean all the jets in the carb again, blew it out with air and put it back together. The first couple of kicks produced the same results. The cleaning of the jets was good test to insure that they were not clogged. I then turned in idle speed screw kicked the bike over an it started right up with a nice idle speed. I did however have to mess with the fuel screw since the temperature around 28 degrees here in NJ. Took the bike for a test ride and it ran awesome!! I would like to say thank you to everyone for their help and input to help me resolve my issue. This site is great!!



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