YZ450F backfire

I have a 2004 YZ450F that constantly backfires as soon as you let off the throttle. Any way to fix this? I've cleaned the carburetor. What's next??:applause:

We need more info...

Has it always done this?

whats your current jetting?

Does it start easiely?

Ext.

My '05 backfires all the time when the engine is working, ie engine breaking down a hill etc. It intensified when I put on my header and pipe but the bike runs great. I think some minor back firing when you let off after high RPM's is normal. right???

When I got the bike new, there was no problem. It just started doing this. It also does not idle. I have not messed with anything. The entire bike is stock. I have cleaned the carburetor a few times because I have let the bike sit for log periods of time in between riding.

If nothing that might influence this has changed, like the weather, the exhaust system, etc., and nothing in the two posts I just linked applies, and it just suddenly started, a possibility that may not have been mentioned is that the hot start plunger may not be seating completely when it's closed.

If nothing that might influence this has changed, like the weather, the exhaust system, etc., and nothing in the two posts I just linked applies, and it just suddenly started, a possibility that may not have been mentioned is that the hot start plunger may not be seating completely when it's closed.

This is a good point. About 6 months ago when I was cleaning the carburetor, I noticed that the plastic nut to the hot start cable where it screws into the cabr was cracked. Maybe upon tightening the screw, I tightened it too much and made it crack. Last week, I just replaced the hot start cable with a new plastic screw. How would I know if the plunger is seated properly?

With the engine running, the hot start should make a distinct difference in the way the engine runs. This is especially true with the choke on, when it will work as if it were a thumb throttle (except that it will have only two speeds). If you can't tell if it's opening and closing, it's probably not doing one or the other.

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