Reduce or Eliminate Popping / Backfiring
A copy of this thread is also located in the CARBS AND FUEL section of the Vulcan Verses
The sound (popping upon deceleration) is created in the exhaust pipes because of Kawi's EPA emissions design. Kawi designed the system to add cooler fresh/filtered air into the exhaust in order to create a second burning of wasted or unused mixture that may not have completely combusted during the times of closed throttle/decels. The poppings you hear are the secondary combustions in the exhaust sounding out
Couple things. First, everyone else is right about the air mix screws. Turn them all the way in (Clockwise, using that very small screwdriver) and then turn them out about 2 turns. If you experience popping, turn them out another 1/4 turn. If that doesn't work, try another 1/4 turn. Keep doing that, but don't go more than 3 1/2 turns total.
Second, when you replaced your pipes, did you use new crush gaskets where the pipes attach to the cylinders? This is a common place for air leaks which will cause popping. Somebody posted the Harley Davidson gasket part number a few days ago that will work on the VN750. Or you can get a pair from JUDGE on the VROC board for $6.00. Also, those acorn nuts tend to work loose a little after changing pipes - check to make sure that they are snug, but DO NOT overtighten - I think they are only supposed to be 12 or 14 ft-lbs. or something like that.
Third, you might want to consider coasters or marbling to cut off the air to those reed valves if you haven't already done so. Some combination of these things should eliminate the popping, or at least greatly reduce it. Good luck, and keep us posted on your progress. I'm curious to learn what works for you. Jim "Pick" Foster Dixon, IL
Last edited by Vulcan Verses; 01-15-2006 at 04:46 PM.