Accelerator pump

[ohsobad_chevy]

I have a 2004 400ex. This carb has an accelerator pump on it nad I was told that there is a small jet in the accelerator pump that you can change to get awesome throttle response. Can someone tell me if this is true and if it can be changed.

[GPracer2500]

Some AP equiped carbs have a leak jet. It is bleed-off jet that controls the duration of the AP fuel squirt. Their sizing works opposite of normal jets, i.e. the larger the leak jet the less fuel gets squirted. I didn't think that the 400EX carb has a leak jet but I'm not sure--not all AP carbs do.

[ohsobad_chevy]

OK, Thanks for the input. Much appriciated. If anyone else wants to add anything, go ahead.

[wilkin250r]

I think the accelerator pump on the 400EX is already properly designed, and I believe GPRacer is correct, the 400EX does not have an adjustable leak jet.

I've heard of a few dirtbikes having problems with their accelerator pump, and a leakjet change can indeed improve throttle response. If the leakjet throws way too much fuel into your airstream, you can bog down. Likewise, if you have too little fuel, it can stumble.

However, not all accelerator pump problems are with the leakjet. From what I understand, the FCR carb for a 400EX is known to have a stumble, but the problem is related to the bowl design, not the leakjet.