Motorcycle Repair: carburetors, straight pipes, vacuum leak

Question
My 1980 GoldwingI   was popping and back firing so I replaced the air valves and cleaned up the carbs and replaced the needle and seats and the accelerator pump but it is still popping out of the exhaust and sounds really crappy at a steady engine speed but over 4,000 rpm or at full throttle it sounds just fine and it runs good.There is no loss of power or hesitation it just sounds bad.Since I put straight pipes on it you can really here it popping.I did also change the jets to accommodate the straight pipes.However after I did those things my fuel economy also dropped in town  but on the highway the faster I go the better the fuel economy.It sounds like a vacuum leak to me but I can not figure out where it is coming from.Do you have any suggestions? I have ran out of idea's.Thank You for your time.

Answer
Schuyler,make sure the mixture screws are adjusted out about 2 1/2 to 3 turns out from seated and take the slide needles out of the vaccum slide and if the are slotted with 5 grooves take the circlip or the [dammit] clips off and move the clip down 1 or 2 grooves raising the mid-range fuel flow and re install move all 4 meedles the same. This will take care of the lean condition the pipes are causing.