66 Mustang 289 Help - Ford Mustang Forum
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post #1 of 6 (permalink) Old 11-20-2019 Thread Starter
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66 Mustang 289 Help

Hello guys first time post. I’m only 16 so I don’t have much experience. I got a 66 mustang for my 16th and I am having some issues. They started about a week ago with no warning. It wouldn’t idle and I managed to fix that. Now it is idling rough or misfiring, I don’t know which. It is now also accelerating in reverse without me touching the throttle. I haven’t put in any forward gear because I am afraid it will do the same. It’s not a stuck throttle since it isn’t doing it in park. It has a Holley Performance Carb. and is also a 3 speed automatic. I’m not sure what is going on but I could use some help trying to figure it out. It also seems that it has started dripping more oil than usual. It’s not a broken motor mount as I have checked that. I don’t have many tools or time since I’m in high school. Any help is much appreciated. Thank you.

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post #2 of 6 (permalink) Old 11-20-2019
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Hi Chase66! I think what may be happening is the fast idle choke system is working and when you put the car in gear you are getting a big accel surprise...…. let the car warm up until the idle comes down. A broken motor mount would have nothing to do with an oil leak....but that are also typically easy to fix. being so new, IMHO it's a little difficult remotely to show someone how to adjust a carburetor, properly replace an oil pan gasket, etc.....Clymer makes a good basic repair book that has lots of good pics too!!!! IMHo, see if you can't find a real hot rodder….(an ol timer with gray hair) who might be able to spend a little time with you......with a little mentoring and the book, you'll be off to a great start!

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post #3 of 6 (permalink) Old 11-20-2019
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You say "it wouldn't idle and I fixed that". Did you maybe speed up the idle by turning the idle speed screw by the throttle linkage?

Making your idle faster will possibly smooth out your engine a little when it's not tuned right (or has a problem) but that also makes other problems, like the car wanting to move as soon as you shift out of park. If the throttle plates are not in their proper position, you may be out of the idle circuit and into the transfer circuit as well, which will make the car very hard to tune.

If it was running ragged all of a sudden for no reason, the first thing to check for is vacuum leaks. After that, check your plugs to see if they are fouled, or maybe just worn and need replacement. Whatever you do, don't start changing your distributor timing and tinkering with all the carb settings. If it ran very well previously, then you know all the settings were right. Changing everything at random will only mean that you need to go back through and fix all the settings you changed, when you finally solve the mystery. You just need to find out whatever's made it start running poorly, and deal with that one thing.
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post #4 of 6 (permalink) Old 11-22-2019
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All the above is good advice. Like they said it is most likely something got stuck. So look at everything from the gas paddle forward. Just look for something binding or interfering.

The choke cams are behind the big black round plastic cover, usually on the right side of the carb. Not inside it, between it and the main part of the carb. You will see a cam with several 'steps' and a 'lever' in line with it.

The basic idea of the choke is to open the big flat choke plate in the center AND lower the fast idle as the engine gets warmer. Until it is hot, then the cams fall out of play and the choke plate is vertical and not longer restricting air flow.

There is a heat sensitive spring inside the black cover which exerts pressure to close the plate and let the idle cam raise the RPM. That is why you step on the gas a little BEFORE starting a cold engine, called setting the choke.

As the spring gets hotter it allows the cam to rotate and the lever steps down to a lower spot on the cam. This happens several times until this cam rotates enough to be out of play and the choke plate should be vertical at this point. At this point the HOT IDLE set screw now controls the idle RPM. And this is usually on the right side of the carb where the throttle linkage is.

Spraying some WD-40 on the cam when the engine is cold may help. Also check that all the vacuum hoses are connected. That all vacuum ports on the carb are covered. Check the vacuum line going down to the trans at the top and bottom. Also the pipe, with several smaller tubes for vacuum lines, behind the carb on the intake. Not all engines have this.

Again - DO NOT change anything like the timing, point gap, etc until you check all the above.

You might ask the local Mustang club for help.
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post #5 of 6 (permalink) Old 11-22-2019
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Check your PCV Valve and hose it could be clogged shut this will make for a rough idle and cause excess oil to come out of the pan because the crank case is building pressure and unable to release it. It may only need a new positive crankcase ventilation valve

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post #6 of 6 (permalink) Old 12-12-2019
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I 2nd thecartguy - my 'similar symptoms' was due to PCV valve gummed up open - could not get rich enough mixture when throttle plate started to open - was bypassing air from venturi when RPM's were still low.
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