Stalling sputtering and backfiring and then comes back to life like slut magic

Ok so I get my bike back from the shit head mechanic after he "fixed" a stalling problem I was having, and now Rees a sporadically spark issue it seams the timing is going in and out of wack and I have no idea why. At one point i lost spark in one of the cylinders and was running one down. And like a stroke of slut magic it came back to life at about 50-60 mph and everything went back to normal and ran fine.

A lot of people are thinking its electrical a lot are thinking water in the gasoline and I'm thinking someone -I LUV XLF!--I LUV XLF!--I LUV XLF!--I LUV XLF!-ed with the carburetor a little to much, original issue was just a spontaneous stall out that would instantly kill the motor, now it's running rough and there appears to be some sort of goblin giggling somewhere near the bottom end.

Now it seams to be set off buy stop and go traffic so far atleast. I'm letting some dry gas clean out the tank right now and I'm gonna start it up tomorrow to see if that clears it up. But I'm wondering if anyone has any other thoughts on the subject. The bike is a 1986 sportster 883, I'm trying to get some second opinions on the problem and to see if anyone would be able to help me figure it out for trouble shooting purposes. Or give me things to try to diagnose the problem.

If this is in the wrong place please lt me know so I can move it please and thank you.