hi i have recently rebuilt my old manual choke hitachi carb with new gaskets and accelerator pump because my new auto choke carb was just rubbish!

so know i tried tuning it i can get a smooth idle at 750rpm but its running too rich the plugs go black is seconds the mixture screw is 5 and half turns out anything leaner and the engine start to sputter so i cant lean it out.

also when the revs are held say at 1500rpm you can hear the revs go up and down like high then low but less noticeable at full throttle! if i lean the mixture out it does this at idle as well then will die!

its running so rich that my choke wont function either in the mornings!

stuff i have checked!

1.air leaks
2.distributor points dwell position and timing

also when i put my hand over the carb to see if their is any air leaks the suction is really strong like it sucks your hand in then dies immediately is this much vacuum normal?

sorry for the long post!