First make sure your timing is right. Then slowly adjust the idle screw at the base of the carb. Turn it in until it stumbles. Then turn it out, counting the number of complete turns, till it stumbles again. Then put it half way in between. Or you'll have to pull the top and unscrew the main jet down in the float bowl. Use a screwdriver large enough that it goes in both slots of the jet. Take it out and read the number stamped on it. Get another one with a number just 1 or 2 lower (smaller size) then what you took out. Type it for awhile and then do it all over again if it's not where you want it.
or get a vacuum gauge and a tach. Hook it up to a valid vacuum source and adjust until you get the best vacuum and idle speed.
