new carb=fast idle?

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Dec 1, 2015 | 01:59 PM

fordguy76

Thread Starter

Laughing Gas

Joined: Apr 2001

Posts: 1,191

Likes: 4

From: West Union, OH USA

new carb=fast idle?

Bought a brand new 2100 2bbl carb for my 66 f100 with a 352fe and it is idling very high (no tachometer). It has all new gaskets under the carb. cannot figure this out tried adjusting the idle screw on the throttle linkage but it has no effect. Is it a vacuum problem?
I put new plugs, wires, cap and rotor button on it the points seem ok.

the old carb idles fine but misses horribly under acceleration.
bought the truck in not running condition. tried 2 other carbs I had laying around and have the same high idle condition?
Timing?

Thanks!

Dec 1, 2015 | 03:02 PM

Tedster9

Post Fiend

Joined: Apr 2002

Posts: 19,311

Likes: 97

From: Waterloo, Iowa

95% of all carburetor problems are ignition related, right?

Can you observe (engine not running!) down the carb throat that the butterflies are closing completely?

Have to be methodical and thorough on these old beasts, no way around it. Yes it's frustrating and takes longer but the results are way better and long lasting.

Do you have a vacuum gauge? A mechanics tach isn't a bad idea either.

Dec 1, 2015 | 03:48 PM

g4g2g7

Tuned

Joined: May 2008

Posts: 253

Likes: 48

From: Somerset, OH

Suggest checking simple stuff 1st. For instance, is the cable even allowing the the throttle shaft to rotate closed far enough for the idle screw to hit the stop? Maybe it's being held open too far by the cable.

Dec 1, 2015 | 05:04 PM

Tedster9

Post Fiend

Joined: Apr 2002

Posts: 19,311

Likes: 97

From: Waterloo, Iowa

He does mention other carburetors have the same problem so it's definitely something external to the carb.

Dec 2, 2015 | 04:47 PM

Becky_is_a_66

Laughing Gas

Joined: Sep 2012

Posts: 860

Likes: 13

From: Asheville, NC

Quote:

Originally Posted by g4g2g7

I suspect the same.

Dec 24, 2015 | 04:44 PM

fordguy76

Thread Starter

Laughing Gas

Joined: Apr 2001

Posts: 1,191

Likes: 4

From: West Union, OH USA

I had a serious vacuum leak between the carb spacer and intake itself. I only heard it after putting in ear plugs... then I could feel it leaking in the rear by the pcv hose. I changed to a different style newer spacer I had laying around which eliminated the leak. But now my linkage IS holding the throttle open as the new spacer is taller!
Do I change the cable linkage out or try to find a shorter spacer?

Idles awesome with the throttle linkage unhooked now...

Dec 24, 2015 | 04:50 PM

fordguy76

Thread Starter

Laughing Gas

Joined: Apr 2001

Posts: 1,191

Likes: 4

From: West Union, OH USA

could I swap linkage with a 70's solid linkage easily?

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Dec 25, 2015 | 09:49 AM

daveengelson

Lead Driver

Joined: Aug 2003

Posts: 6,305

Likes: 18

From: Boulder Creek, Ca

Not an authority, if adjusting idle mixture has no effect then I would suspect a vacuum leak; also check to determine if using the correct source for the vacuum advance; metered vs unmetered?

Suggest first establish TDC. I use a quick check method by removing #1 plug, place finger in the plug opening and with ignition off, rotate engine and immediate stop when compression forces finger out of the opening. I then check which plug wire the rotor is firing to the timing marks, should be aligned with #1 plug wire.

As member mentioned, if suspect vacuum leak at the carb spacer try short burst of carb cleaner and see if there's any increase in RMP. Anyhow, food for thought?