DavidOfMA wrote on 11/24/12 at 16:58:18:What's odd about the 55 jet on a stock bike?
I had gone out to 3 turns on the idle mix screw with the stock pilot jet and I was still getting a lot of backfiring. Now, with the 55 jet, the idle mix screw is about 1 1/4 turns out. Unfortunately, still backfiring. Tried the 55 jet when it turned out the TEV was fine. Going up on the jet was an attempt to increase the richness of the mix to stop the backfiring, since I couldn't go out any further on the idle mix screw and make any difference.
I'll try tinkering with it a bit more, but 1 1/4 turns seemed to give the best idle speed today (at about 45 degrees outside, sea level).
Have people here been successful at eliminating backfiring on this bike with stock air box and exhaust?
What's odd is that a stock engine with stock exhaust just does not need need more than the 52.5 pilot. I have a 2006 with stock engine and header with just a muffler change, and it is a pretty open muffler. I have the 52.5 pilot set at 2 3/4 turns out and it is nearly backfire free. I had no backfires at all initially but the exhaust has since loosened a bit from the quick install I did so I need to go back and tighten it up. Point is that the 52.5 is just about all it needs. It is borderline but it is darn close. A stock engine with stock muffler will not move as much air and so will not need as much fuel. Since your stocker is still backfiring then there is another issue that is affecting the engine and making it backfire.
Typically, an air leak in the head/header and/or the header/muffler connections is the other cause of backfiring.
You said you were adjusting the pilot screw to reduce the backfire. That is a secondary but desirable effect of the tuning process. When you are tuning the pilot screw your goal is to achieve the best (highest) rpm when the COMPLETELY WARMED UP engine is idling. When you find that point, if you turn the screw either left or right the rpm will decrease. Then you know you have found the best setting. With that setting, adding no more than maybe a quarter turn for a dash of extra fuel to help that last little bit for any backfire left over. At this point you should be at least 95% backfire free, with only a rare shot...if not totally free.
I would not expect a stock engine with stock exhaust to go beyond 2 turns out on a 52.5 pilot.
With your situation where you have a 55 pilot and still experiencing backfire, there is an air leak somewhere. I would bet your exhaust is messing with you or perhaps there may be an air leak between carb, mounting flange & head as well.