Need help on proper adjustment to carb for my 70's 250 single barrel

[j_cst_10]

I've rebuilt a couple of those style carbs, not that one in particular but they all operate similarly. Float height is a big deal on that style of carburetor and can dump unwanted fuel into the engine if set improperly. I pulled my 1bbl apart on my old 59 chevy and the floats were put in upside down.

Sound like you may have a float issue and/or a vacuum issue. Check for vacuum leaks and look down the carb when it's running. Is the idle set high because of a stumble when trying to accelerate or because it won't idle? Some more details are needed to nail down your issue.

As for carb adjustments, you have 2. Idle speed and mixture and it sound like your problem won't be fixed with a simple idle screw adjustment, but you can try. Turn the screw in and count the turns, then set it back where it was. Adjust it in 1/2 turn increments, if the truck responds better then great, if it doesn't try adjusting it out the same way. If you find this is your problem, get out a vacuum gage and connect to manifold vacuum and set the screw for the highest vacuum setting and best signal while maintaining a constant idle rpm.