I was going to suggest that as well. I have a harley that develops intake leaks every once in a while and it does the same thing. Pops, crackles, and farts off idle but runs decent when you open it up. cracking the throttle open it just sputters and pops untill I get passed it. Of course now its fixed. Try the spray technique like in the previous post.you may have a vacume leak also..spray wd40 around the carb base and anywhere a leak can pop up ..also make sure the vacume advance can on the front of the dizzy is working right..might be frozen from rust or what have ya..