Even though the bug is running better, still getting a little backfire wither idling or if I start to slow down when I'm driving.

Went back and looked and the plugs on the drivers side 2&3 are still sooty, smutty, black powdery looking.  1 & 4 look great. I've looked for leaks and haven't seen any.

Any other tips as to why or what to look for as to why the only those two plugs look black (running rich ?, carb still may have crud? ) and could this be realted to why I still get a little backfire.


Thanks
Ron