67 GTO 7027262 Fast Idle

[rickmpontiac]

I have a recently restored 7027262 on my 67 GTO that idles at about 1,000 rpm. I

[rickmpontiac]

My previous post was truncated.

I have a recently restored 7027262 on my 67 GTO that idles at about 1,000 rpm. I adjusted the idle mixture screws and running at operating temperature with choke fully disengaged I cannot adjust the idle speed. The stop on the throttle arm is not touching the idle speed adjustment screw. It is actually backed out all the way. I can put pressure on the throttle arm and get the idle speed down to about 800-850 rpm. I removed the carburetor to look for anything obvious like damaged throttle plates, throttle shaft binding, etc. I checked for vacuum leaks and ignition timing.

Any thoughts or suggestions?

Thanks,

Rick

[WideTrack]

Twisted throttle shaft?  Or the plates weren't closing all the way when they were torqued down on the shaft during assembly?  Or too much idle bypass?

[77cruiser]

Are the secondarys closing all the way?

[Cliff Ruggles]

If you are using the 1967 factory intake check to make sure the correct gasket is used under the carb with the stainless steel shim gasket on top of it directly against the carburetor.

Check the timing to make sure it's not too advanced.

Assuming no vacuum leaks anyplace check the throttle plates in the baseplate to make sure they are closing all the way and sealing tight in the bores.....

[rickmpontiac]

I removed the carburetor and checked the throttle plates for binding and closing completely. I used 1/4 inch strips of paper to check for consistency around all four plates while closed. I  tried different timings w/o vacuum advance between 6 and 18 degrees at idle. I can get the idle RPM down to about 800 w/o vacuum advance. Connecting vacuum to the advance from either the ported or manifold brings the RPMs up to 1150 to 1200. All of this while at operating temperature and choke fast idle not a factor.  I could adjust the idle speed down to where the car would die with the Edelbrock #1407 that I removed to restore the originality of the car. It does have a 67 cast iron manifold with the the heat crossover. I currently have the stainless steel plate sandwiched between two correct gaskets for the manifold. I added the top one trying to make sure there was no vacuum leak between the carburetor and base plate.

[Kenth]

7027262 do not have a ported/timed source for the vacuum advance, it is manifold vacuum in that port.
Leaking hot idle compensator at rear of float bowl?
Flange gaskets/plate installed upside down?

[rickmpontiac]

The Pontiac Service manual says vacuum advance should run off manifold vacuum so looks like I'm good to connect it either place. I've verified the gasket and stainless steel plate are installed correctly. I do have a gasket between the stainless steel plate and the carburetor in addition to the one between the plate and the manifold. I'm not familiar with the hot idle compensator so may check into that.

[Cliff Ruggles]

Pontiac Q-jets in 1967 will use HIC.  I'd block the hole under the HIC as the HIC valves are known for leaking and causing high idle issues.  It really isn't needed anyhow....

[rickmpontiac]

Thanks Cliff, I will take a look at it. Appreciate everyone who provided suggestions.

[rickmpontiac]

I removed the carburetor today and confirmed the HIC has been plugged. See attached picture.

I also checked to make sure all the throttle blades were centered in the base plate.

The car idled fine, meaning it could be adjusted down to 500-600 RPM with an Edelbrock Performer manifold and Edelbrock 750 CFM carburetor. I installed a correct casting cast iron manifold when I installed this carburetor. All this to restore the originality of the car.

Is it possible that I have significantly more vacuum to the distributor advance now (24 degrees advance at idle) with this configuration?

Just trying to determine what would contribute to the high idle speed.

[Kenth]

Timing is fine, factory setting is 6 degrees BTDC initial plus 20 degrees from the vacuum advance.

Air is getting past the throttle somewhere. Common leak paths include the carburetor and throttle body gaskets, carburetor insulator spacers, intake manifold gaskets, and of course, any of the engine vacuum fittings, hoses and accessories. Another overlooked item can be a worn throttle shaft.
At this point i would look at the throttle body gasket for correct style and the intake surface may have been milled in the past to fit milled cylinder heads causing an intake manifold gasket leak?

[rickmpontiac]

Thanks everyone for the advice and lists of things to check out. I am still doing some investigation and will be back with more information soon.

[Mr.Pontiac]

Rick the hole in HIC is not ware screw is , it’s on top of the HIC passage towards top of bady

[firebird400]

Thx for this post here guys & Gals , I have similar issue and will be using this info to deal with my situation.