I've got a 76 xl175 basketcase that needs help. I've got the girl running just fine but it feels like there is something wrong with the mixture. I get a fairly good run up through the RPMs but at the same time get some sputtering from the exhaust and carb. Also when i snap open the throttle it bogs, but if i slowly open then snap it revs right up. I've checked the timing and it's good so now i'm playing with the air screw and clip position. but cant seem to find any good balance. The spark plug is not fouling so i dont think its overly rich, but because of the backfiring i'm assuming it may be the case. Any ideas where to start with this thing....i'm starting to get frustrated!! Thanks so much in advance!