CRF450R Fire out the Exhaust

[mideastrider]

Never had this issue since bike was new. Its an 08 and purchased from dealer in March of 2010. If you rev the engine way up or just bump the throttle just before settling back down to an idle it will pop and crack once maybe twice blowing blue flame out the exhaust 12 inches or more. The bike starts up easy (1 kick) and has good power. I checked the valves 2 weeks ago and the left side intake was tight 0 clearance. Had a race the next day so I shimmed it. Ran the race without a problem. So last week installed new intake valves. Ran the race this weekend with no problems except on the last lap or two it began this popping on decel. I have went through the carb which was clean as could be. Thinking its a lean condition thought there might be a clog. Double checked the valve clearance and ok. Played with the fuel screw but not finding anything that will make a difference. I need a clue?

 

[Ol'89r]

Could have an air leak in your exhaust system. Introducing cold air to a hot, partially unburned mixture inside the pipe will cause the condition you described.

 

[mideastrider]

Thats interesting I will check that out. Because my son came in from riding late friday and I noticed his header had a bad kink right in the bend. I was leaving for Ohio saturday morning and he was staying to run a local race. I was going over the normal things that needed to be done to the bike for him to race it sunday and oh yeah change your header. He swapped the header so I will give that a check this afternoon.
Very well could be something loose or not fitted up right.
Thanks

 

[whenfoxforks-ruled]

Put a 50 pilot in it and the flame can get 4 foot long. Vintage Bob

 

[mideastrider]

I got home pulled the header and sure enough there is a crack about 1 inch long about an inch from the head. This was the old stock header that had some damage but not leaking that I had replaced some weeks ago with a pc ti header. Ti lasted no time til bent. I have a new SS pipe coming tomorrow. Thanks O'89r

 

[Matt90GT]

if that does not solve the problem, you need to check the hotstart plunger in the carb. Remove it, clean it, put a light film of grease on the plunger, reinstall and then make sure you have slack in the cable

 

[mideastrider]

New header fixed the problem. No more cracking or popping and no more flames.
Thanks