An easy backfire question!

[Grouper]

Im starting to get somewhere with the carb settings on this bike. Its running better now after Another good carb cleaning and a float level adjustment. But now im getting a slight backfire when im coasting and im off the gas.
Is this a lean condition? Should I raise my throttle needle up 2 spots?

 

[dirtbkr188]

Backfiring on decel is usually indicative of a lean condition, try turning the air screw a 1/4-turn IN to richen it, and ride the bike to see what happens. If it improves, try another 1/4-turn, etc. If it gets to the point where you're within a 1/2-turn of fully seated IN, it's time to go up a size on the pilot jet.
You could try raising the needle (lowering the clip) one notch, and see if that helps, raising it two notches at once is kind of radical, imo. Combining the two adjustments above may be all you need to clear it up.

 

[b52bombardier1]

It could be a lean condition that will possibly take a main jet size increase to fix. Or you might have an exhaust leak where the pipe meets the head. Did you use the fuzzy, cloth-covered circular washer-gasket there?

Rick

 

[Grouper]

Thanks Guys! I turned the pilot screw in 1/2 turn and moved down 2 needle clips. Its Almost gone! this morning im going to turn the screw 1/8 turn farther and see what happens!
Thanks Guys!

O sorry, My exhaust gasket looked like a metal 2 piece half circle. Wouldnt i hear or feel it leaking from the exuast if that was the culprit for my backfireing?

 

[69ST]

If the exhaust O-ring is leaking, the headpipe & muffler can become a part-time afterburner. On closed-throttle deceleration, a fair amount of unburnt gasoline vapor can accumulate in the exhaust stream...and, vacuum can exist at the port/headpipe flange interface. Oxygen mixes with the combustible exhaust gases and "bang!". It's not the only cause of this, but the most common.

You probably won't be able to feel an exhaust leak in this location, even with a rotted headpipe. It might not even be audible. There's not much backpressure in the stock exhaust, particularly when the engine is not under heavy load.

 

[dirtbkr188]

Those two half-circle pieces are not the exhaust gasket, they are the collars that go between the pipe flange and the flange you slide up onto the exhaust studs and bolt up to the head. The exhaust gasket is one-piece, and usually stuck inside the exhaust port on the head. It goes in place before you slide the pipe into the head.

The diagram on the left is the original microfiche, on the right is what I mean above...

 

[Grouper]

hmm... lol! I hope it stayed stuck in the head, Cause I never saw it! But if the intire gasket was gone, Im sure I would be able to hear that?

 

[69ST]

They usually do remain stuck in the head, in usable condition to boot. But, they don't last forever and can sometimes be a bugger to completely remove. When in doubt, pull the exhaust and take close look...no substitute for inspection.