Motorcycle Repair: 1998 Suzuki Intruder Backfire/Spit/Sputter, rich fuel mixture, vance and hines pipes

Question
I have a 1998 Suzuki Intruder VL1500 that when given more than half throttle spits and sputters and barley has any power for a 1500.  Its very slow, and when you let off the throttle it backfires a lot.  It has vance and hines pipes, but no other modification as far as I know.  Any suggestions would be helpful.  

Answer
Michael,
check the compression first just to make sure
both cylinders are even.
Sounds like an air leak on the intake or
a plugged main jet in carb.
Is it running on both cylinders?
Check the plugs to see if they are white (lean)
or black (rich) fuel mixture.
Air leaks on the exhaust can cause backfire too.
See if gas is getting to the carbs okay.