I rebuilt a 1963 ford 2100 2 barrel carburetor out of a truck with manual choke. I put it on and it has a bad idle and dies requiring the choke to start it again. Thought it was a vacumn leak but sprayed WD-40 with no change in idle. So I took it off and put the previous carburetor with the electric choke on it and the idle is great so I thought it is not a spacer intake leak. What could be wrong? I have it on a 272 Y-block 1960 ford manual tranny. Appreciate any help.

My experience is that on the 2100 or 4100 nearly always there is dirt or crud somewhere inside the booster.

One way to tell is if you can get it to idle at all, then close the choke plate slowly after it warms up. If it speeds up suddenly as the plate is nearly closed, it could be either a vac leak or dirt in the booster.

I'd pull the carb and the booster assy and clean and blow it out carefully. I've actually had cases where I did that, and then it ran good, but after a few minutes of driving would pull more crud back into the holes inside the booster. Clean, clean, clean. But at least then you have found the problem.

I will was going to check for vacumn leaks then pull it off. I have ran it until warm then close the choke plate and it runs better. I was going to check for vacumn leaks then pull it off. Any special way in checking for leaks? If I can't find any I will check the booster. Have you known of the channels in the carburetor becoming clogged? Thank you for the reply.

Checking for vac leaks:
Squirt oil around any suspect areas like vac fittings, power brake hookups, and especially the base of the carb gasket/spacers, that is a classic vac leak area.

My next step is always to put the carb back on but with a different spacer or no spacer if you can, and some good gaskets that seal all around. Look for passages where the manifold and carb and gasket dont quite match up and air could sneak in.

But the dirt in the boosters is my most common trouble.

dirt in carb:
Sometimes in the 2100 the idle holes in the main body will plug or rust. If you pull the mixture screws out with the carb off, run a wire thru that hole right into the throttle bore. That's the easy hole to clean but there are a couple other tiny transition holes in the throttle bore right above them, very fine wire will clean them.

Well I checked for vacumn leaks and found none. So I took off the carburetor and took it apart again. Concentrated on cleaning again all passages. And then I found the problem. I looked at the venturi booster and found one of the air tubes was clogged. I can't believe I missed it. Cleaned it out, re-assembled it and put it on tonight. I finally got a low curb idle of about 500 rpm with out the surging, missing, and curb idle of 800 rpm just to keep it running as I had before. What a difference a little occlusion makes. Thanks again.