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MX997

YZ450F backfire

8 posts in this topic

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:

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We need more info...

Has it always done this?

whats your current jetting?

Does it start easiely?

Ext.

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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???

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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.

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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.

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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?

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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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