Help - idle speed too fast

[scumdog]

Ok, the carb on my '66 'bird had it idling too fast so I took it off and put a 780 Holley on, it didn't make it runn as well as I wanted so put the original carb on.

Now it idles even faster!!

I checked for:
Throttle linkage sticking - it's not.
Vacumm leak - disconnecting and plugging the lines made no difference.
Choke - adjusted it so the flap was straight up and down
Hold-down studs - the nuts are all snugged down
Dash-pot - adjusted it so it's not making contact

So any other ideas???????😕

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[RichKing]

Carb

You took it off and then put it back on..... Did you use a new gasket? Did you clean the manifold of the old gasket mater that stuck to the manifold or carb?

To check for a base gasket leak... Have the car running and then spray some carb cleaner around the base of the carb where it meets the gasket... If you hear a change in RPM the base gasket is leaking.. make sure that when you tighten the carb down you cross tighten the bolts.... Looking at the top of the carb you can start anywhere my example is starting from the left rear...

Left Rear
Right Front
Left Front
Right Rear....

SNUG FIRST
THEN go back a second time to final tighten...

Do not over tighten you can twist the base of the carb...


Rich King
NNJ

 

[RichKing]

Carb

You might want to stick a VACUUM gauge on the engine and see if the vacuum is correct and not erratic....

Rich King
NNJ

 

[Ward 57]

Ok, the carb on my '66 'bird had it idling too fast so I took it off and put a 780 Holley on, it didn't make it runn as well as I wanted so put the original carb on.

Now it idles even faster!!

I checked for:
Throttle linkage sticking - it's not.
Vacumm leak - disconnecting and plugging the lines made no difference.
Choke - adjusted it so the flap was straight up and down
Hold-down studs - the nuts are all snugged down
Dash-pot - adjusted it so it's not making contact

So any other ideas???????😕

I had the same problem with my '57. I was assuming the springs on the carb were strong enough to pull everything down to an idle. I did the same with the dashpot and leaned up the chock so it really wasn't functioning.
I adjusted the throttle linkage to the carb by turning it out a couple of turns so that the throttle linkage return springs actually pushed the throttle plates closed as those springs are much stronger. Was then able to make the dashpot and choke functional again.

 

[Frankie the Fink]

Most carbs have a "transfer slot" which aids in moving from the idle circuit to the cruise circuit. Sometimes, in chasing that perfect idle, you can tweak the mixture/speed screws so that too much of the slot is exposed....whereupon you can't get the idle speed down and the mixture screws become ineffective... Looking at the throat of the primary from the bottom the transfer slot should be nearly square with the plates closed, you can adjust the speed screw to achieve that then try re-tuning mixture and idle.

The SECOND most common problem is the timing is too advanced so check that as well...