Carb tuning issues

[mammentorp]

I'm revealing the limits of my experience with 4 barrel carbs here, but need some input because I'm spinning my wheels (not literally).

I've rebuilt my Autolite 4100 and installed back on the engine. I went through the bench adjustments with the shop manual and with much viewing of Mike's Carbs videos. The car (63 hardtop w 390) starts great but seems to be running at a fast idle speed (1500 RPM) and I can't get it to settle down. I believe I have the choke adjusted reasonably well. It's at full choke when cold and after a few minutes it starts to open up, per this pic:

The fast idle adjustment screw does not appear to be contacting the cam:

Also you can see from that pic that the secondary circuit is closed, as it should be.

Frankly the choke/fast idle mechanical linkage is confusing to say the least. I'm sure I'm missing something very basic here.

Any suggestions?

[Cheshire]

Vacuum leak?

[Karl]

Is the accelerator linkage holding the butterflies open? Try disconnecting the accelerator linkage at the carburettor with the small clip.
Do you have to move the lever on the carburettor to have the hole line up with the linkage?
Karl.

[mammentorp]

Is the accelerator linkage holding the butterflies open? Try disconnecting the accelerator linkage at the carburettor with the small clip.
Do you have to move the lever on the carburettor to have the hole line up with the linkage?
Karl.

I don’t think that’s it. I removed the linkage when it was running and the link slides in and out of the hole on the throttle body actuator easily. The main and secondary butterflies seem to be fully closed, even tho the engine is running at 1500+ the whole time. Things appear to be rich as well - black spooge coming out of the tail pipe.

[mammentorp]

Vacuum leak?

Wouldn't a vacuum leak translate into a leaner condition? I do see something of concern at the base of the spacer. I installed with a bit of Permatex Aviation sealer on the spacer gaskets. One side appears to be dribbling a bit?

[Karl]

Did you take the butterflies out and remove the shaft?
Or they were left alone.
Also maybe the dashpot maybe holding the throttle open slightly.
Karl

[mammentorp]

Did you take the butterflies out and remove the shaft?
Or they were left alone.
Also maybe the dashpot maybe holding the throttle open slightly.
Karl

The dash pot isn’t installed yet…. I did take the butterflies out. Are you thinking I might have gotten them reinstalled incorrectly? I was careful, but could always have made a mistake.

[Karl]

G'day.
Maybe they are not closing properly and one is holding the throttle open slightly. They can move when you go to tighten the holding screws up.

I would double check everything else before pulling the carb down again.
You could always just take the carb off, remove the top cover and choke and hold it up to some light and see how much of a gap is around the venturi and the butterflies. Did you mark the butterflies and place them back into their original place?

The black spooge that you talk about coming out of the tailpipe could just be because your mixture screws are not adjusted properly because it is running to high.

Karl.

[mammentorp]

G'day.
Maybe they are not closing properly and one is holding the throttle open slightly. They can move when you go to tighten the holding screws up.

I would double check everything else before pulling the carb down again.
You could always just take the carb off, remove the top cover and choke and hold it up to some light and see how much of a gap is around the venturi and the butterflies. Did you mark the butterflies and place them back into their original place?

The black spooge that you talk about coming out of the tailpipe could just be because your mixture screws are not adjusted properly because it is running to high.

Karl.

Indeed, I took the carb back off and the butterflies were NOT closing completely! I removed them and reassembled on the shaft and now they close beautifully. Something was not quite right.

This is the second 4100 issue you've identified for me from literally the other side of the planet. I feel as though I should send you flowers.

[Karl]

I'll pass on the flowers - Happy that I was able to help.