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the stock specs from ford were

M Trans A Trans

800/500 575(600/500)


Higher idle was if the car had A/C


however these numbers would be meaningless with a new cam.

anywhere from 500-800 could be normal.


basically tune for what the engine wants not what you want.

don't trust the old factory tach if you have one use an external tach meter for a more accurate reading. the factory tach could be 200 rpms out of calibration.

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With a cam you have to tune the idle for your desired drive-ability, if you want it to lope at idle then you're going to set it lower but that can lead to an off idle stumble if you're not that experienced with your carb. You should find a base idle that gives you a good feel, probably around 10-14 degrees with a 2bbl, then set the idle preferably with the car in gear (that can be difficult to do safely, a friend helps). When you add a larger cam, even a mild one, you're going to tend to have a higher idle than you would like in park and neutral.


In short I think you should shoot for around 650-750 with it in drive, probably be closer to 950 in park, but the timing will make a difference in idle speed and quality.

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Also I have heard of guys turning their idle down way too low just so it sounds like it has a big cam in it and have done damage to a flat tappet cam. I usually shoot for around 750 in gear with auto trans idling. With mild cam. In park it is what it is if you set the in gear idle to 750.

1971 Mach 1

408C Stroker - C4 w/3,000 stall - 8.8" Rear w/3.73's - Disc brakes all way around.



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I've always set idle at 600 rpm in Park, which drops to 525 +/- in gear. That's with 14 deg initial timing and the choke fully disengaged. If the carb is properly tuned and there are no vacuum leaks, it should run just fine.

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as others have posted, set the idle with the car in Drive foot on brake, Turn the headlights on, and if you have A/C run the compressor.


the headlights on will Tax the electrical system so you want the idle set with the engine loaded.


it is true when the car is in park the idle will rise up sometimes a lot but it needs to be that way to have a smooth idle in drive.


on my car the factory recommendation was like 725-750 in gear, headlights on with the A/C running.

I find i need to have it at around 800-850 to have a smooth idle in traffic and when i put it in park she will go to 1000 rpms.

basically you throw the book specs out and do what the engine wants.


another consideration, Heavy stopping. a higher idle will also help heavy braking stall out, even if you have the floats set correctly sometimes the engine loads down so much that it will stall in a panic stop. a couple rpms more on idle can stop that.


you might be uncomfortable with the idle higher then you feel it should be but overall the car will just run better.

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Have you checked whether the idle stop solenoid is out of adjustment and pushing on the carb throttle too much? If you turn the AC off does the idle drop from 1300rpm? If so you just need to adjust the solenoid. I think 700 rpm should be about the target.



351C 4V cc heads, 10.5 : 1 CR, 290 Herbert cam, Flat top forged pistons, forged connecting rods, Atomic efi,

C6 with Gear Vendor overdrive, 3.89 Tru Trac, Hooker Super Comp with 2 1/2" Pypes Exhaust.        


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