Stage 1 Low rpm backfire

firstly thankyou for adding a video allways helps

can u tell me how the bike performs in all revs ?

you say it has been dynoed how long ago ? have you made any changes since ? was it working fine when it left or has it been like it since u got it back from them ?

does it lack power taking off ?

first thoughts its almost certenly the carbs if not possibly a problem with the powercomander but id say 99% sure its carbs but if you took it to pros they shuld have set it all up right

what do it think it could be im thinking sounds like fuel mix problems low end maybe pilot ajustment needed possibly carb sync problem but all should of been addressed at the dyno center

can i also ask how long ago it was dynoed ?

as for something usefull for now here is a little rule for thigureing out air fuel mixes at low rpm and as a genral rule for setting up any stage of the carb idle mid and high rpm

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• NOTE: A rich problem gets worse as the engine heats up.
• If the throttle is lightly "blipped" at idle, and the rpm drops below the set idle speed, then rises up to the set idle speed, the low speed mixture screws are probably set too rich: try 1/2 turn in, to lean the idle mixture.
• NOTE: A lean problem gets better as the engine heats up.
• If the throttle is lightly "blipped" at idle, and the rpm "hangs up" before dropping to the set idle speed, and there are no intake leaks and the idle speed is set at less than 1000 rpm, the mixture screws are probably too lean: try 1/2 turn out, to richen mixture. Be sure there are no intake leaks and the idle speed is set at less than 1000 rpm!
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Check for an air leak at either the exhaust manifold or the intake manifold. Backfiring on decceleration usually indicates a lean issue but can also be caused by a leaking exhaust gasket. Rough idle can be caused by an air leak as well. The easiest way to find a leak is to spray carburetor cleaner around the intake on the cylinder head. If the engine speed picks up you have found your issue. Also what are the modifications if any on this bike?

Is the idle speed set too low? If so, adjust it, using the idle speed adjusting screw, to the correct idle speed (900 RPM). If that's not the problem, then check for air leaks between the carburetors and the engine by spraying WD-40 around the intake manifolds with the engine running. If there is an intake leak, the engine RPM will change briefly when the WD-40 is sprayed near it.
Aside from that, there are two other things that can cause your engine to die when it should be idling: the idle speed mixture adjustment, or low cylinder compression. Of course, if it was idling fine before, and the idle mixture adjustment hasn't been changed, then do a compression check, first. To idle properly, each cylinder's compression needs to be at least 140 psi.

Here is the common cause of surges (idle speed goes up and down), stalls at stops, slow idle speed, erratic idle speed, rough idle and engine hesitation (and other problems), it is in most cases the idle speed control air-bypass valve and or throttle valve and upper intake, these area's get full of gunk and combustion residue over the miles and cause idle issues (stalls, low idle) like yours, Get a can of intake cleaner from any local parts store, not carb spray, intake cleaner, it is made by a company called CRC, remove the air intake hose to the engine, hold the idle high so the engine won't stall, then spray the can of cleaner into the intake while keeping the engine running, use at least 1/2 the can, shut down the engine and disconnect the battery for 5 minutes, then restart and complete a number of mixed driving cycles, town, freeway, stop and go etc., after a few days the problem will go away as the system will relearn to the clean intake.