850 double pump issues HELP!!

hemitt said

ok well went to preformance shop guy told me to take 45 power vavle and put in prim. and i put 75 prim 80 sec. still got prblm...its back firing out of carb first with black smoke then caught on fire... so i think i said before i had 50cc pump but i might be wrong which ever one is the smaller im thinking 30cc?? so ima try the bigger acc. pump see where that takes things now

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That carb takes 80 jets square (all around with PVs F&R), if you block them off (either end) run 88 jets as a baseline, that carb should have NO problems on its factory cams/squirters, there should be a 31 & 30cc with pink cam (#1 hole) up front & a 50cc pump with a brown cam & 31 or 33 squirter out back, for some reason your going "lean" on the transition.

And when your trying to make changes to a carb, make "little" ones, not "BIG" ones. If i was there i'd have that carb singing, as long as it hasn't been jacked with too much or is all screwed up. A 4781 850dp is a very simple carb, there fairly straight forward, easy to tune, really it sounds to me like its all fucked up in the metering.