07 YZ450 Backfire

So I had a oil leak at the right side crankcase down below the kickstarter. After waiting for over a month on gaskets I finally have it back together. I took it up and down the street and it's backfiring when I let off the gas. It didn't do it before I took it apart so it must be something I did. The only thing I added was a gasket where the pipe meets the head... there wasn't one there before.

Maybe it just needs to be tighten more? Or maybe I should just remove it? Thanks

Here's what you did that caused it:

...waiting for over a month ...
I got $5 on a varnished pilot jet. If you have access to a set of small number drills, and you have a 45 pilot, push a #77 through the jet. A piece of wire from a fine wire brush can do the job too.

Carefully.

I will give that a try for sure.

I just pulled the head pipe to see if I missed pulling the old gasket and I sure did. So I pulled the old one and put the new one back in. Put it back together and I still have the backfire.

What I noticed is that the head pipe gets really hot within a minute of the bike running.... does that sound normal? I just don't recall it getting that hot that fast. I also replaced all the hoses with CV4 hoses. I noticed a little bit of fluid from the weep hole but it's only a few drops and then it stops.

I also have Dr. D exhaust and had the cone shaped noise deal in it. I pulled that out and put the regular screen back in. Bike sounded a little better after that. Also the gas in the tank is kinda old, a little over 2 months and it’s almost empty….could that cause a backfire as well? Thanks for the help

I will give that a try for sure.

I just pulled the head pipe to see if I missed pulling the old gasket and I sure did. So I pulled the old one and put the new one back in. Put it back together and I still have the backfire.

What I noticed is that the head pipe gets really hot within a minute of the bike running.... does that sound normal? I just don't recall it getting that hot that fast. I also replaced all the hoses with CV4 hoses. I noticed a little bit of fluid from the weep hole but it's only a few drops and then it stops.

I also have Dr. D exhaust and had the cone shaped noise deal in it. I pulled that out and put the regular screen back in. Bike sounded a little better after that. Also the gas in the tank is kinda old, a little over 2 months and it’s almost empty….could that cause a backfire as well? Thanks for the help

your pilot jet is clogged. Clean it and fresh fuel.

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