Have ยด80 850 special. I know the vacum line on the left petcock leaks a little gas into the intake. Need to rebuild I guess. Would this cause really bad gas mileage and a hard accel miss? I took carbs off to adjust the mixture as I think it is too rich but the needles are factory pre-set, do I have to change the jets and are they available? All the plugs have a black soot around the electrode, but gray on the center. Also I am running a MAC 3 into 1 exhaust, do I need to rejet for that? The instructions from the manufacturer said no. Thanks a million.