>Food for thought. Make sure your butterflies can close
>Otherwise... you'll probably never be able to get a normal idle.
The SU has got to be arguably the simplest carb yet designed this side of the pond, with the possible exception of the Wick Carb designed by George Lanchester.
>From what I've been reading on SU threads over the last few weeks, it still seems that some people are getting in a hopeless tangle tuning them.
Plenty's been written on how to go about it and checking the butterfly closes fully is the very first step in preparing to retune. If it doesn't shut completely, its the throttle stop screw holding it partially open (as you mentioned) or the butterfly spindle has worn. I've come across very few cases of the latter, though no doubt there have been exceptions of which I remain ignorant. At the risk of being repetitive, the starting point for setting up an SU is
a simple six fold check:
Each carb has to be adjusted individually for mixture with the other one totally shut off. Ain't no way you can do two at the same time. When mixture is the same for both, air intake is regulated using a Unidoodlywotsit - or, a piece of rubber pipe. Alternatively, you can do it "in stereo" with an old stethoscope.
It's only AFTER all this other work has been done, that the interconnector pins are put back into the throttle yokes and tightened. People who fail to do this and think they can adjust their carbs with two locked yokes will NEVER get it right.
Now in the same museum as the cars he sold when they were new