Author Topic: High RPMs, how to bring it down?  (Read 204 times)

Offline jaxops

  • Mark Monaghan
  • Posts: 392
    • CLC Member
      CLC Member #24591
High RPMs, how to bring it down?
« on: June 17, 2017, 05:56:35 AM »
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?
1970 Buick Electra Convertible
1956 Cadillac Series 75 Limousine
1949 Cadillac Series 75 Imperial Limousine
1989 Ford Crown Victoria Station Wagon
1997 Lincoln Town Car
AACA, Cadillac-LaSalle Club #24591, ASWOA

Offline The Tassie Devil(le)

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  • Posts: 7471
    • CLC Member
      CLC Member #18992
  • Name: Bruce Reynolds
Re: High RPMs, how to bring it down?
« Reply #1 on: June 17, 2017, 06:15:48 AM »
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. >:D
'72 Eldorado Convertible (LHD)
'70 Ranchero Squire (RHD)
'74 Chris Craft Gull Wing (SH)
(Past President Modified Chapter)

Offline V63

  • Posts: 330
  • Name: W Link
Re: High RPMs, how to bring it down?
« Reply #2 on: June 17, 2017, 06:20:39 AM »
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.

Offline jaxops

  • Mark Monaghan
  • Posts: 392
    • CLC Member
      CLC Member #24591
Re: High RPMs, how to bring it down?
« Reply #3 on: June 17, 2017, 06:24:14 AM »
Thanks- the plates are closed at idle so I will check the other suggestions.
1970 Buick Electra Convertible
1956 Cadillac Series 75 Limousine
1949 Cadillac Series 75 Imperial Limousine
1989 Ford Crown Victoria Station Wagon
1997 Lincoln Town Car
AACA, Cadillac-LaSalle Club #24591, ASWOA