Motorcycle Repair: carbs., vf750 magna, k n air filter

Question
my email is bill78688@sbcglobal.net my bike a 1997 vf750 magna c2 i just had dyna jetts installed (108 main jets) needles on clip #3 and the shop had the air screw (slow jets) at 2 rounds. I set them @3 turns at first i set them @2&a half turns it seem to top out a little fast at 2&a half turns But @ 3 turns it pop less on decell i have a k/n air filter and cobra drag pipes with only about one inch baffles cut the other 11 inchs off so in other words just enough baffle for a little back presure. I heard some people say not to tune the air jets for less poping like i did.What do you think? And do you think my bike topping out faster @2&a half turns-&5mph slower@ 3 turns had to do with the adjustment or maybe just differant road condions like wind?  Thanks,Bill  

Answer
Hi Bill,

Tune the carburetors for optimum air-fuel mixtures through out all carb ranges. Adjusting the "air-fuel screws" affects idle and off idle ranges.

Deacceleration backfiring is associated with air cut-off diaphragms, lean air-fuel mixtures, valve timing, and pipe design and modifications.

What are the colors of the spark plug insulators? Perform plug chops and read spark plugs to know what changes to make with carbs to obtain correct air-fuel mixtures.

I'll send carb files to your email.

Respectfully,
Mark Shively