Author Topic: 67 gt500 idle settings  (Read 306 times)

waltweems

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67 gt500 idle settings
« on: April 15, 2019, 08:07:23 AM »
I have the original holly 600's and the hot idle is 1000 rpm but cold idle is too low and I want to adjust them higher by turning the screw under the carb counterclockwise but want to know if I should increase both carbs or just one and, if so, which one.

Thanks for the advise.

Wat Weems

shelbydoug

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Re: 67 gt500 idle settings
« Reply #1 on: April 15, 2019, 09:27:03 AM »
First you adjust the hot idle to where you want it. Then you let the car sit overnight and you adjust the choke idle screw.

I believe that should be about 1800 cold at start. It should start to step down after about a minute in two steps.

Until it's hot, it won't idle below 1100 or so.

If you have an automatic trans, you're screwed. You'll need to cheat those numbers down until the brakes can hold the car at hot idle.

You want to verify that you have the correct choke thermostat. If it says Holley on it, that's the wrong one?

I'm not sure if the auto trans and the manual trans use the same choke thermostat? I don't think so. You want the slower kickdown, not the faster one.

waltweems

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Re: 67 gt500 idle settings
« Reply #2 on: April 15, 2019, 12:25:28 PM »
Doug,

Thanks for your advise.  I assume the choke idle screw is  the one under the carb.  Should I adjust them on both carbs?

Walt

shelbydoug

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Re: 67 gt500 idle settings
« Reply #3 on: April 15, 2019, 01:35:35 PM »
The choke idle screw is on the choke lever. The carb curb idle is in the "throttle pate body".
The secondary carb you just want at  minimum in order to have fuel flow through it to refreshen the fuel.

You don't want it affecting the idle rpm. You want to control that with the primary carb, i.e., the carb with the choke in it.

With the stock cam you should be able to get it to idle at 800 or so. If it's automatic, then the stall speed of the converter is involved. Still, stock should be very civil.

A advertised 280-282 cam should idle around 950. If you want to play with the distributor you can do better.

I've got my Pantera with Webers and a 292 cam in it idling at 750 so don't give up thinking it's impossible.

The PCV valve is also involved in this since you loose idle vacuum through it and some are worse then others. Typically 2 to 4 inches at idle since few if any completely close at idle like they are supposed to. That raises the idle speed requirement as well.

1967 eight barrel

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Re: 67 gt500 idle settings
« Reply #4 on: April 15, 2019, 07:05:51 PM »
The only screw you would be adjusting from the bottom would be the fast idle cam setting. The secondaries have a set screw that is in the throttle plate, but I don't recommend touching that. The mixture screws are on each side of the metering block and of course the idle screw is facing up at an angle and sets the curb idle.  I am running a relatively healthy cam and I have it where it idles well at about 850.
Perhaps my irritation is the rich idle.
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shelbydoug

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Re: 67 gt500 idle settings
« Reply #5 on: April 16, 2019, 10:56:21 AM »
The only screw you would be adjusting from the bottom would be the fast idle cam setting. The secondaries have a set screw that is in the throttle plate, but I don't recommend touching that. The mixture screws are on each side of the metering block and of course the idle screw is facing up at an angle and sets the curb idle.  I am running a relatively healthy cam and I have it where it idles well at about 850.
Perhaps my irritation is the rich idle.
                                                                                -Keith

On my small block, I took two 83 Mustang GT Motorcraft/Holley carbs. Converted them to 1850 bowls and used them on my 2x4 Holley set up.

First off they use annular venturis. Second, they are factory calibrated to 14.6 at idle. They came stock with 59 mains. The idle is SO clean stock you can't see any deposits on the plugs AND they are dulling the finish on the ceramic on the headers.

I've been working on these things to FATTEN up the idle to save the headers. You need to work with jetting the idle air bleeds on that. You would be SHOCKED to see how clean the idle is. SHOCKED.

I upped the mains to 64's on the carbs but I think they make as much power with the 59's?

If you are not married to being "correct" I'd recommend ANYONE go this route with a 2x4 Holley set up on the street.

Now a race car is going to be different. You MIGHT even want to reverse the linkage to face the carbs forward with that? Maybe?