Just picked up a 03 450f and have some questions (back firing)

Okay so i just picked up a 450 for a pretty good price, sadly its already the end of the year. Anyway, the main question i have is about the back firing, it starts decent, has a lot of power, but when i let off the gas it back fires loud, my initial guess was its running way lean... if i ride with the choke on, its back fires a lot less, and when it does its quieter. Im guessing its the fuel mixture? I have one of those easy access mixture screws on the way. Another thing is the idle is way too low, however the idle cable seems to be seized... any ideas on how to loosen that up? Its so low the bike will stall after about 30 seconds of trying to idle.... however with the choke on it will idle all day. Thanks ahead of time for any advice you guys may have for me...

I have only been aware of backfiring being caused by 2 things- A/F mixture or an exhaust leak.  But if adjusting your A/F is making the backfire going away, then that is your issue. 

 

 

Always start by checking for a loose fit of the header at the head and at the mid pipe joint.  If that's the cause, you can sometimes cover the problem up some with richer idle mixture, but then you have a bike that's too rich with a leaky exhaust.

 

If the bike sat for some time with the carb dry, it could also have a film of dried varnish in the pilot jet.  A number 45 pilot is only .018" through the metering orifice, and an .001" film on that will not only make it backfire and act lean, it might barely even stay running at idle.  Check the fuel screw, too.  Run it all the way down against the seat a time or two, and check to see if the O-ring on the screw (above the spring and washer) is in good shape (no cracks, etc.)

Throw a new pilot in there sounds like where id start after any obvious intake or exhaust leaks

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