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Join Date: Nov 2007
Location: Chandler, Arizona
As was said, it can be more than one thing. Definitely remove the complete air injection system, and if it is a CA model, the complete evap system. The air injection injects air into the exhaust, causing it to run hot, and can cause popping and backfiring. The evap system can cause it to run either too lean or too rich. Next, if they are still there, remove the plugs covering the pilot screws on the carbs, turn the screws in until the seat lightly, then back them out 2 1/2 turns. That is a good starting point, you may need a little more or a little less. Make sure the gas tank is properly vented.
If none of these things help, then there is most likely something wrong inside the carburetors. But I would try all the other stuff first, as it needs to be done regardless if there is another problem.
If you have altered the intake or exhaust, all bets are off. The Vulcan has a very carefully engineered intake and exhaust system, and if you modify it, it can create all kinds of issues. The intake and exhaust systems determine how the air/fuel mixture flows through the engine at all engine speeds, and even a minor change can upset everything.
I am a motorcyclist, NOT a biker.
1997 Vulcan 750, purchased about a week ago
2006 Sportster 1200 Low
2013 Royal Enfield Bullet 500, converted to carb
2001 Yamaha XT225, heavily modified
2004 Honda Rebel 250
1979 Vespa P200E
2002 Vulcan 750 parts bike
1994 Yamaha XT225 parts bike