dont know whats wrong

[exkid04]

whats up i just put a stage 2 hot cam in my 01 400ex it has pro circuit t-4 slip on, k&n filter, WB rev box, brand new carb with 152 jet bike sounds and runs good when i accelarate but when i let off the throttle it backfires real bad and then sometimes it wont idle and sometimes sounds like it is sucking air somewhere i think i might have a little exhaust leak coming out where the headers connect on the to studs on the motor

[ryanh250ex]

First and foremost, verify that you have no exhaust leaks or air leaks near the airbox or carb.

I have had air leaks before, they have produced very similiar problems.

152 sounds a little lean, whats your elevation?

[exkid04]

latly i have been riding at about 3,000 feet but mostly ride at sea level i tried a 158 jet but it didnt fix the problem

[ryanh250ex]

I'm convinced it's an air leak. I'd also go back to your 158 jet.

[wilkin250r]

I think your idle problem and your backfiring problem are the same issue.

When you're at idle, you are not giving it any throttle. Simple to understand. But think about your other problem. When you accelerate, and then LET OFF THE THROTTLE, you are also at zero throttle, aren't you? In both situations, the slide on the carb is down all the way.

Your carburetor isn't attached to your crank, it doesn't know what RPM you are running at. When the slide is closed, you are running on the pilot and air screw, regardless of what the engine RPM is. The needle is at the fattest part, the main fuel passage is almost completely plugged. So even when decelerating, you are on the idle circuit of the carb. Changing the main jet won't fix the problem, because it's not on the main jet.

If you're backfiring, you're lean. I think your pilot is too small. This should fix both your backfiring AND your idle problem.

Now, if you have an air leak, that's a completely separate issue, and this should be the FIRST thing that is addressed. It can also cause a lean condition, and no amount of pilot jet replacements will fix it. First and foremost, check for an air leak.

[exkid04]

what are some good ways to check for air leaks

[ryanh250ex]

spray suspect area with carb cleaner. the rpms will fluctuate if you get a spot with a leak