Motorcycle Repair: Carb problems, stock air filter, air fuel mixture

Question
QUESTION: I have a 1986 Sportster that I just purchased and it's basically bone stock. It does have 1 3/4" drag pipes on it. The problem I am having is at idle it seems the carb is loading up. When I ride for about a 1/4 mile it spits and pops and surges. Then it backfires and runs fine for any distance until I come to a stop again. The process then repeats. Jet numbers are 155 and 52 from what I can remember. Like I said the bike runs absolutely perfect after this low idle loading problem. No hesitation, surge, or anything. I am concerned the jets are the wrong size for the drag pipes. I don't want to burn an exhaust valve out. Does the vacuum switch only "work" when the throttle is open or does it do work at idle too?

ANSWER: Pull your plugs and let me know what color they are
Mike

---------- FOLLOW-UP ----------

QUESTION: both plugs have alot of carbon deposits on the metal by the threads, but the electrodes are still real clean.The plugs were new about 1500 miles ago. No sign of pre-ignition or fouling. The carbon leads me to fuel loading. I do have the stock air filter on this thing. Could i be choking it out? Like i said, after 1/4 mile at 55MPH it pops and clears out and runs fine. What do you think?

ANSWER: I would check the air/fuel mixture screw port and the intermediate jet for dirt.
Good luck and happy riding
Mike

---------- FOLLOW-UP ----------

QUESTION: I got home tonight and pulled the air filter off. Took it for a ride and it ran perfect all the way up and down the spectrum. I thought the residue in the air cleaner was from backfiring but every time i had it idling i saw fuel spitting out of the carb. i'll check what your talking about but i have a funny feeling the idle jet is way too big. Thanks for your comments Mike. It's been a pleasure but i hope i don't need to talk to you anytime soon.
Brett

Answer
Since you said your biek is stock and probably have a stock carb, you dont have a idle jet. the air/fuel misture screw is for idle. Once just off idle the intermediate jet takes over. Since the plugs are not fouled the jets are not to big. Fouling would cause the tips to get black. The pipes are causing the gas to spit back since there is no back pressure on the exhaust.
Good luck and happy riding
Mike