2001 sportster backfires when bringing the revs up

Most likely due to a dirty/ faulty idle air control valve. If it is all gummy inside, the valve can’t open or close properly to maintain idle. This is usually mounted on the intake manifold near, or directly on the throttle plate area. Be advised that if you replace it, the first time you start it after replacing the engine may rev up to around 4,000 rpm until the computer kicks in to bring the valve closed, usually takes about 10 seconds.

Your description indicates a serious fuel starvation problem but a very weak spark could cause or aggravate the condition.

You need to reset the throttle position sensor.

It sound like map sensor when it under load it bring the revs up

ck your distributor, the cap and rotor, if all are good ck timing to see if jumped time. if in time and distributor ok ck fuel, and look for vacuum leaks.

Backfire through carb often means timing too advanced.

Make sure you have enough freeplay in your throttle cables. They're located up by the twist throttle.

"Backfiring" is a pretty broad term depending on where you live. Some people refer to backfiring as popping from the exhaust while others refer to it as the engine spitting through the carburetor.

I'll assume that you're talking about popping out the exhaust pipe. If it does this after you rev the engine and it backfires on the way back down to idle, this is typical of an exhaust system sucking air. The mixture is extremely rich under these circumstances and will not ignite. But, if your exhaust system is sucking air, it combines with the fuel air mixture already there and bring it to an explosive mixture thus the backfire.

You can check you valves but I've always found that if the valves on an Ironhead are too tight, it's extremely difficult to get it started due to the low compression on that cylinder.

Check you ignition timing and points setting. Also, what kind of condition is your mechanical advance in the distributor in? I'm assuming this is an XLH model and not the magneto equipped XLCH.

What type of carburetor is on the engine? Hopefully not the original Tillotson that it came with. If it's an S&S, the low jet should be a 28 and the main jet a 66 to 70.

Possibly bad tpos sensor

Bad idle air control valve

Bad maf sensor

Check the computer codes first before spending any more money on it

Also do a compression check

And check your valve timing and ignition timing just in case.

Ok, due to different terminology used by different people, I'm going to assume that by "backfire", you mean it pops through the exhaust system when you back off the throttle. On stock exhaust systems which use the "crossover" connector to connect the front and rear pipes, the backfire is usually caused by an air leak somewhere in the exhaust system.

When you back off on the throttle, the mixture is usually too rich to burn in the exhaust system. But, if you have an air leak allowing the scavenging effect of the system to **** air in, the mixture becomes combustable and is ignited by subsequent exhaust pulses.

Check your exhaust system gaskets and replace them if necessary. This should stop your problem. Rejetting the carb may be necessary as well.