My 88 duke is having problems with backfiring through the exhaust after about 5 minutes of driving, anything before the motor is warm it runs great. And within 15 minutes of driving it will be popping thru the exhaust so bad it sounds like a gun going off in town and you fear it may die or not get up to 30mph in town. Highway driving isn't possible. The car ran great before and one day it suddenly did this. I know the car has a strong motor and was rebuilt 30k miles ago without a hiccup until now. I thought I'd try the unplugging the MAP sensor buy it didn't help. The check engine light isnt on and I don't know where to start. The car has had a complete tune up within the past year and has newer fuel pump and filter. (fuel pressure is good) I'm thinking maybe a coil? Any help is appreciated. The car has the egr blocked off but I doubt thats anything related. It ran great without it earlier. Thanks
