High RPMs, how to bring it down?

[jaxops]

I had my carburetor rebuilt on my 1956 Cadillac and they set the idle speed to 1,000 rpms....somehow  Timing and dwell are spot on, and it actually speeds up when you set the air and idle screws to "4 turns out from set."  The are in about 1.5-2 turns out from all the way in.  I suspect that they changed my pedal but I don't see any change on the nuts and pedal connector.  Any ideas?

[The Tassie Devil(le)]

There are a number of ways it could be high.

(1)   The choke idle adjustment set too high.
(2)   The throttle plate adjustment too high.
(3)   The throttle linkage adjusted too short.
(4)   A vacuum leak.
(5)   Distributor Vacuum Advance adjustment not to specs.  (The timing will change as the engine revs drop, especially the mechanical advance)
(6)   The secondary throttle plates not adjusted to be fully closed at idle.

I would have thought that these engines would normally idle at around 450 to 600 RPM.

Bruce.

[V63]

First step would be to verify the throttle plates are closed at idle. If these are adjusted 'open' it's the same effect as you pushing on the accelerator pedal at idle. It could also be stuck on 'fast idle' cam on the linkage. If your car has AC, there is also a step up (fast idle) solenoid for that.

[jaxops]

Thanks- the plates are closed at idle so I will check the other suggestions.