[zgears]

im reposting this from britbike,
so i rebuilt my s.u mc 2 carb. new gaskets , polished inside the dashpot, auto choke slides fine. it gets gas, but it doesnt seem to get into the motor. i fooled around w\ the base nut that controls the mixture, but notting. what am i missing here?

 

[lilbill]

was the motor running ok with the stock carb before you hung the su on it ? in other words is the su the only variable here and we don't need to worry about cam timing or other shit on a new rebuild ?
the su is pretty bone simple. the butterfly valve opens allowing air to flow thru the venturie which causes negative pressure on the top side of the piston which lifts the needle out of its seat in the main jet allowing fuel to enter the air stream. actuating the choke lever lowers the main jet allowing more fuel to flow out. some carbs have "ticklers" which are just buttons you press down on to depress the float and flood the venturie with raw fuel. if air is going thru the carb and the main jet is not blocked the motor should be getting gas. try holding the throttle wide open while you kick and when the motor "kapoffs" thru the intake, shut the throttle and kick till it starts. an su like an amal requires a certain "ritual" to start.
also make sure the butterfly is cracked open about 1/32 with the idle screw. you can fine tune the idle and mixture once it starts.
almost no carb swaps are "plug 'n play"
haynes puts out a good book on tuning an su