66 Mustang hesitation when pressing gas - Ford Mustang Forum
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post #1 of 6 (permalink) Old 09-23-2018 Thread Starter
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66 Mustang hesitation when pressing gas

Hello to all,

I have a 66 Mustang convertible with a C4 automatic 200 cubic inch 6 cylinder. It had been sitting for a while and wanted to get the car driving and running better. I have relatively new gas in the tanks and seems to still have the problem.

I pulled the Autolite 1100 carburetor and rebuilt and found many issues. I think I now have them all corrected and reinstalled the carb recently. The care is now idling very well, and runnin very well. It is not missing and seems to drive good. The only issue that I have been able to resolve is a hesitation that I get when you first punch the gas at a dead start. If you continue to press the gas it will stall and if you back off and then repush it will go fine. Once driving the car runs fine.

It seems like this is a accelerator pump issue but I have it adjusted per the manual specifications. It is in the HI position and set to 3/16" gap with the throttle plate closed.

I know that you have adjust the linkage by bending if this gap is wrong but my gap is not wrong. (I beleive). Also the float was adjusted in the carburetor to 1 1/32" distance based upon manual.

I know that I will get in trouble with the purists but I did replace the poitns and condensor with a Petronix ignition and this did not seem to help the problem. It also did not seem to hurt the problem either.

Any help would be appreciated.


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post #2 of 6 (permalink) Old 09-23-2018
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If there are no vacuum leaks it could be dirty intake manifold or valves. Does the car have the exhaust seats for unleaded gas installed?

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post #3 of 6 (permalink) Old 09-25-2018
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Changing out points for a Pertronix is a no-brainer. Make sure that you run a new wire from the ignition switch "run" terminal straight to the distributor and bypass or abandon the old wire. The Petronix needs a full 12 volts, but the original circuit has a resistor in it that will give about 6.

You can try adjusting the accelerator pump for more or less squirt but before you do that make sure that the distributor advance is set up correctly.

Make sure the crankshaft damper is zero at TDC.

Make sure that the vacuum advance on your distributor is connected to full manifold vacuum. Initial advance should be 6 to 8 degrees and vacuum at idle should add about 15 for a total of 21-23. When you press the throttle manifold vacuum drops, retarding the spark until you release the throttle and settle in for cruising.

This is important because the carb enriches the fuel mixture for acceleration by both the accelerator pump and power valve. Rich mixtures ignite faster, requiring a spark advance to be retarded.
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post #4 of 6 (permalink) Old 09-26-2018
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By your symptoms ( dies on a hard press but accelerators with a softer touch) I'd be looking everywhere for a vacuum leak! Especaily where the line to the transmission transitions from steel to rubber.

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post #5 of 6 (permalink) Old 11-08-2018
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Although there has been no frequent update to this post, my take is twofold....
1. A 6 cyl is not "torquey". It's torque that get's a mass moving.
2. With a 2.80 rear, and weighing in at 2.8 - 3K lbs, it's "not" going to jump up and run away from a dead start. So, the hesitation, as long as, all other aspects are inline, will still be there.

Just my 2 cents.

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post #6 of 6 (permalink) Old 11-08-2018
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I agree with all of the above points, but I understand the difference between a stumble and a general lack of power. I think I'd double check the timing first, and then test the carb with different accelerator pump settings, as you suggested.

Snapping the throttle plates wide causes the timing to fall flat on its face, as vacuum advance goes away. I'm not sure if you have the Load-O-Matic dizzy or the standard version, but either way, if your timing is too conservative, when you go to full throttle and you don't have enough base timing, your car will hesitate.
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