i have a 2001 sportster 1200xl custom and on the way home from work today just about home i noticed a noise when i would get on and off the gas. hard to describe the noise but when i would hit the gas it would "clunk" and then when i would let off the gas it would "clunk". If i would ease into the gas it wouldnt make the noise or ease out of the gas it wouldnt make the noise. it reminded me of a bike with a chain and it being loose and when you would hit the gas it would take the slack out of the chain and make the noise, so the belt was the first thing that i checked and it seemed tight. doesnt do it sitting still and mostly in any gear except for first. sounds like the noise is coming from real low in the bike but not sure where. if anyone has any idea in which direction i should be looking it would be very nice.
Thanks

 

Loose primary?

 

Concur.

 

+1 - (To be a bit more specific) - The primary chain needs adjusting.