backfiring/pop/crackle | GTAMotorcycle.com

backfiring/pop/crackle

wantsabike

wantsabike

Well-known member
so I have a 04 ktm 625 smc that has a pro circuit t4 slip on on it and everytime I let off the throttle it back fires like a mother trucker... maybe not so much of a backfire but it pops/cracks like crazy any time I let off the throttle no mater what gear no matter what speed.... is it something should be concerned about ? or is it normal for these machines to do that with a slip on like this, or does it need to be "repacked"
 
Exhaust leak at the head could do that.
 
wantsabike said:
ahhhh that may be the culprit then, I bet I have a leak where there silencer slips on the factory pipe
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A leak there would not be the problem.A leak at the cylinder head would.Did you recently remove the header pipe or place any force on it out of the normal?
 
It could also be a bit lean, that is the most likely scenario

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nope have not pulled the pipe off the head or anything since ive owned it, maybe the previous owner did im not sure...but it still has the factory header pipe on it

best way to check if is lean is take it for a ride and yank the plug correct ? when driving it before pulling the plug do I need to pound on it hard, or just regular driving habits
 
wantsabike said:
nope have not pulled the pipe off the head or anything since ive owned it, maybe the previous owner did im not sure...but it still has the factory header pipe on it

best way to check if is lean is take it for a ride and yank the plug correct ? when driving it before pulling the plug do I need to pound on it hard, or just regular driving habits
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That will work if the plugs aren't a pain in the *** to get to. Run it at a given throttle setting for a bit and hit the kill switch.

Another easy way is to cover part of the air filter with duct tape. It will give you less air, and a richer mixture. If the bike runs better, it's lean.
 
spray____ said:
That will work if the plugs aren't a pain in the *** to get to. Run it at a given throttle setting for a bit and hit the kill switch.

Another easy way is to cover part of the air filter with duct tape. It will give you less air, and a richer mixture. If the bike runs better, it's lean.
Click to expand...

oh wow ive never heard of that before covering the air filter with duct tape that's new....i'll have to take a look and see if the plug is a PITA to get at or not on this machine....if it runs lean is it or will harm anything ?
 
Short term your bike isn't going to explode or anything like that, but long term it's not good. Lean engines run hot, so it's harder on the engine.
 
Change the pilot jet to the next size up.
 
Lean on pilot circuit. Fatten up the pilot and/or lift the needle. It sounds like the transition from top of throttle to bottom is too great. Make the step smaller and it should solve itself.
 
Ahhh, ok wasn't sure if it the jetting or what.... Anyone wanna give me a hand with doing this ? I haven't been in a carb on a bike like this for a super long time
 
People might think you're still in Mildmay, should update your location. Does that model KTM have the Mikuni BST40?
 
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