79 Harley Davidson Shovel-head burps at around 40mph what needs to be done?

Get rid of the Koffin' Keihin carburetor and use the S&S super "E" or put a Yost power tune kit in it to fatten up the off-idle and part throttle mixture, 40 mph cough sounds like you upshift too early ....drop it down a gear and see what it does Buy somthing 30 years newer.