1950-1966 [Subscribe to Daily Digest] |
1) Do NOT even attempt to adjust the carb until you have all the ignition problems completely solved. Not only is it futile, but if the timing is too far off, the engine can backfire through the carb while you are adjusting it. This backfire may manifest itself as a foot-long tongue of flame shooting up from the carburetor, which is exciting but tough on the eyebrows. (No, this is not a joke! Ask me how I know...)
2) Once the ignition is all per spec and you're sure you do not have any air leaks, it's pretty easy. There are individual methods for every Weber (or other) carb, but on carbs that are in good shape to begin with, I've had good luck "dialing them in" with this generic procedure:
-- Get the engine fully warmed up.
-- Gently turn in the mix screw until it bottoms, then back out 1-1/2 turns. Turn out the idle speed screw until it just barely touches the throttle linkage, then turn in 1/2 turn.
-- Start the engine and let it idle. If it won't idle, turn in the idle speed screw until you find a setting where it will run at 1000 rpm (a little slower is OK, but no faster.)
-- Now turn the mix screw IN a half-turn, and note whether the engine runs better or worse. If better, keep turning in until it runs the smoothest. If worse (more likely) go back to the original setting, then turn it OUT 1/2 turn and see if it runs better.
-- Once you know which way to turn it, keep adjusting the mix screw in 1/4-turn increments until you find the speed at which it runs the smoothest. If during this process the idle speeds up, back out the idle speed screw to return it to the original speed.
-- Once you find the best position, turn the mix screw back in until you JUST hear a TINY deterioration in idle quality. This setting is "lean best idle," the best compromise between smoothness and not fouling plugs.
-- With the mix set, turn the idle speed screw until the engine idles at 1000 rpm. (Yeah, I know, the original factory specs called for a slower speed, but we know better now: 1000 rpm gives you a little more oil pressure and circulates the coolant a bit faster, all of which makes the engine happier.)
Two notes:
1) If your carb was NOT in good shape previously, and had to be rebuilt, get a Weber manual and set it up with the correct "bench settings" before you put it back on the car, so you'll have a standardized starting point.
2) If turning the mixture screw in or out does NOT change the idle quality, you've probably got an air leak somewhere. You've GOT to find and fix this, or you'll never be able to get the carburetion right.
Good luck and have fun!
posted by 68.13.13...
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