Motorcycle Repair: back firing on deceleration, aftermarket pipes, honda 500

Question
1984 Honda 500 shadow, backfires on deceleration , and hesitates when going from 4000 to 5000 rpms. if i leave the choke on 1/2 way it seems to solve the problem.cleaned the carbs and checked the valve gaps, didn't make any difference. but when i tried to sync the carbs , when the carbs were synic the bike would not idle right,could not turn the idle down it idled too high.had to reset the carbs out of sync for the bike to idle right again. help
seems like one cylinder is putting out more exhaust fumes than the other ,have nothing to test the cylinder compression, but if synic of carbs is off would one cylinder have more compression than the other?? again i will repeat if i leave the choke on 1/2 way bike runs fine and does not backfire on deceleration ,carb problem or something else???

Answer
Hi Steve,

The carbs need to be in perfect sync for the bike to run correctly. If it stalls out or revs too high when the sync is perfect, then you need to use the idle adjust screw to set the idle back to a normal level (usually 900 to 1200 RPM).

The combination of back firing on deceleration and hesitation in the mid RPM range seems to indicate to me that the bike is running lean. Running the choke half way will richen the mixture. Again, this indicates the bike is running lean when the choke is off.
Does this bike have aftermarket pipes? Has the air box or air filter been modified or changed in any way? Are the carbs running stock jetting?
Any changes to the questions above will affect jetting and make the bike run richer or leaner.

Bottom line though, the bike should be running fine with the carbs in sync and the choke off. If you have to change either of these for it to run correctly, then it is compensation for something that isn't right.

Hope this helps,
-Jeff