acceleration problem - Ford Mustang Forum
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post #1 of 12 (permalink) Old 4 Weeks Ago Thread Starter
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acceleration problem

car idles good but when you step on the gas pedal, the car is very jerky and wants to die. I replaced the fuel pump with a Carter and it stills does it. Has a reproduction coil and starter solenoid. The mustang starts up fine and has a 1/2 tank of fuel. The mustang is a 1964 1/2, 289 with a 4 speed. The car was running good one day and then the next day, boom. Any ideas?

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post #2 of 12 (permalink) Old 4 Weeks Ago
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car idles good but when you step on the gas pedal, the car is very jerky and wants to die. I replaced the fuel pump with a Carter and it stills does it. Has a reproduction coil and starter solenoid. The mustang starts up fine and has a 1/2 tank of fuel. The mustang is a 1964 1/2, 289 with a 4 speed. The car was running good one day and then the next day, boom. Any ideas?
Carburetor acceleration pump. When gas pedal is suddenly depressed, a big gulp of air tends to slow or stall the engine. This is prevented by a pump attached to the carburetor throttle linkage which, when the throttle is opened, squirts a small amount of fuel into the airstream entering the carb's secondary venturis.

You can check this yourself. Remove the air cleaner so you can look down into the carburetor, engine NOT running. Use a flashlight if needed. Move throttle linkage by hand: a squirt of gas should be seen going right into the carb. If it's not there, replace the pump, which is actually a small rubber diaphragm attached under a cover plate on the lower front part of the carb, which must be removed to access the pump.

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post #3 of 12 (permalink) Old 3 Weeks Ago
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I would be checking or replacing the fuel filter, it could be that simple.

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post #4 of 12 (permalink) Old 3 Weeks Ago
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Yep, I'd look at the filter first too, then the carb and look for vacuum leaks (or listen for them) and if you still don't see a cause, look at the filter on the pick up in the tank, they can decompose over time and if it's the original there's a good chance it's shot.
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If its jerking, bucking and almost wanting to stall i'd check vacuum first and throughly. Luckily on a 4 speed car there aren't a lot of vacuum points to check. Get a can of staring fluid and the straw from a can of WD 40, with he engine tuning spray each vacuum point and the elngthof each vacuum hose slowly. If you find a point were the engine suddenly revs up there the leak.

Poor throttle response or a bog and delay before acceleration is more indicative of an accelerator pump diaphragm or poor fuel flow
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I'D RATHER GO SLOW THAN NOT GO AT ALL
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post #6 of 12 (permalink) Old 3 Weeks Ago
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Rebuild the carburetor. If it's a 4bbl make sure you have the parts for the vacuum secondaries.

If you have never done one then it can be a daunting task, but it shouldn't be. Back in the day I could do a 2 barrel in 20 minutes. Walmart sells a gallon of cleaner to soak parts in- looks like a paint can. Take a picture at every step, look at the diagram in the rebuild kit and make sure that you put the check ball(s) in the right hole(s). Make all the adjustments while reassembling and then the final adjustments on the car.

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post #7 of 12 (permalink) Old 3 Weeks Ago
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When was the last time it was tuned up?

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post #8 of 12 (permalink) Old 3 Weeks Ago Thread Starter
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It was tuned up this year.

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post #9 of 12 (permalink) Old 3 Weeks Ago Thread Starter
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Would using ethanol gas over a period of time do this?

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Quote:
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Would using ethanol gas over a period of time do this?
Yes. Many of the alloys used in old carburetors dissolve in ethanol. This ends up with white deposits that can clog the tiny passages.

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post #11 of 12 (permalink) Old 3 Weeks Ago
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Quote:
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Would using ethanol gas over a period of time do this?
I would say its highly unlikely. I have been using ethanol fuel in our 2 Mustangs since I bought them c1980 because it was, still is, required for us who live at high altitudes. I have seen no indication of anything unusual, no damage, nothing. I have never had an internal passage clogged just the normal, brown 'dirt' from fuel evaporating from the exposed surfaces in, and around the carb barrels. Open your carb and look in. If you see any corrosion I will be greatly surprised. Mine looks like the attached photo which was taken 12 hours after shutdown. I haven't touched the insides of that carb in 10 years and I drive it regularly. Just after that photo was taken we drove it 3,500 miles round-trip from NM to VA.

I do know of lousy carb alloys that dissolve over time. Ford didn't use any of them for the many Fords I have owned.

The photo does show you why you can have hard starting problems after your engine has been hot. About half of the gas is gone from the float bowl by the time the engine cools off. That will happen with any gasoline whether or not it has ethanol. Without an electric fuel pump that means you may have to crank the starter a few seconds longer to re-fill the carb bowl.
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post #12 of 12 (permalink) Old 3 Weeks Ago
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Quote:
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It was tuned up this year.
Go over your tune and see if anything changed. Operate the throttle with the engine off and see if you have 2 solid streams of fuel spraying from when its first moved to wide open.
Quote:
Originally Posted by 64must View Post
Would using ethanol gas over a period of time do this?
Absolutely not, unless your running old rubber lines that are susceptible to degradation from ethanol.

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