OK. I installed a 2 brothers slip on, the N1TC needle with clip on 2 slot from the top, drilled the slide vent hole to 7/64, changed main jet to #122. Still backfires on deceleration. Any suggestions please.

 

I recently installed an FMF pipe, 122 main, 38 pilot, drilled slide vent to 7/64, and anN1TC on second slot. I was getting pretty bad backfire/popping on decel when closing from WOT. I moved the clip to the third slot and the popping virtually went away. However, this caused a overly rich condition to where my plug was covered withblack powder (carbon fouled). The rich condition was also evident from the mild stench of fuel and the fact that I ran through a tank of gas in about 80 miles or so.

Fix one problem, cause another... So I moved the clip back to the second slot. I also had the Koubalink FAS which while cool in concept, did not allow for fine tunning as it was so hard to turn. I put the stock FAS back in at 2 turns out. The decel popping is not too bad at this point.

I would stay on the second slot, consider bumping up your pilot to a 38 or 40, and make sure your FAS is set properly.

The best troubleshooting I can recommend is to swap out your plug each time you make a change and then check it out after a few miles of riding. And if you do determine a fix please let me know. I'll do likewise.

 

With the HMF pipe I had popping until I went to the #40 pilot, now it's fine.

 

I'd been running the 40 pilot and 125 main for quite some time and the plug showed it was on the rich side of ideal, not fouled but a dark tan. It also idled down at stoplights, not enough to quit but idled down. This spring when I took it out of cold storage I changed the plug and since then I've been getting alot of decel popping so I upped the a/f to 2 turns out then 2 1/4 then back to 2 and it decreased somewhat. (I had it at 1 3/4 to start with). The other day I found that the plug I put on the vacuum line on the carb had rotted away and it was most likely sucking air. I replaced it and now even at 1 1/2 turns out with the #40 it is too rich down low, idles down at stoplights and blipping the throttle will kill it. After it dries out (stupid rain) I'm going to go back to the stock pilot and see where that gets me.