I am having a problem with backfiring through the carb on a 2006 Sportster XL 1200. It has had a stage 1 kit installed. I replaced the 45 pilot jet with a 48 and it helped a lot but I am still getting an occasional backfire. The engine idles fine and runs great at WOT. I have a slight flat spot now between idle and WOT. I have the idle mixture screw out 4 turns with the 48 pilot jet. I'm sure I'm too rich now but I still get an occasional backfire. Does anyone have any suggestions? Thanks, Mike

 

Is it an outright backfire or just a spit? Do it when it's cold or hot? What main jet are you running?

Regardless, sounds like a small vacuum problem. Sometimes when you've had the carb off, the grommet will look good, but they just don't seal well especially after being off several times. 48 is way too rich and 4 on the screw is an overkill too. Generally 3.5 gets you all it's going to give, (comfortably)

If you're confident the o-rings on the manifold are good and the grommet, only other thing (usually) could be the enricher valve not seating well. That's kinda hard to check for but generally the cable **** should lack a tiny bit of going all the way in... And, if they're running rich, that's possibly your "flat" feeling and that can cause a spit or pop when warmed up.

Float setting is really improtant too on the CV. Fuel needs to be exactly to the top of the bowl flange, plus or minus 1mm. There's a good way to check it, let me know if you want to "go there."

 

I see alot of cv carbs that have a small cough. A 180 main and 46 slow jet should do fine. 2 1/2 to 3 turns from soft seat should be plenty.