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1964 1/2 Mustang with vacuum problems

2254 Views 12 Replies 6 Participants Last post by  Fatboy94
Hello to All,

I'm new to this forum and I'm looking forward to increase my knowledge and interest by speaking to you.

I have a 1964 1/2 Mustang Coupe, white, blue interior, 289 with Holly 4b carb.

I have a problem and need some assistance. If I connect the vacuum line from the carb to the dist. the car coughs and sputters. If no vacuum is connected the car runs great but rich. Timing is set at 6 but will run great at 3 all the way to 12. Bottom line Vacuum cannot be connected to the dist. or it will run poorly.

By the way my username Fatboy94 is referencing my 1994 Harley Fatboy

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welcome home! glad to have you
Welcome to AFM... Let's look in here for help.
I'm assuming you have checked the timing with a light & have set it with the vacuum disconnected. What does the timing change to when you connect the vacuum?
Nothing changes at all with timing with the vacuum connected or not. Only that when the vacuum is connected and you increase rpm's it starts to sputter and cough. At idle the engine sounds great with the vacuum connected or not. Timing is 6 degrees.

Hello Fatboy94,
I too say welcome.
Now for some ideas and there are several.
1. - Take Dist cap off and see if the plate that holds the points moves (rotates). You will need to use a screwdiver to push the plate.
2. - Connect vac line to distrib - Then try to adjust the idle screws.
They are on the pass and driver side of the carb (metering block). If you have a double pumper there will be 4 screws.
3. - Spray the carb and distributor vac area with stater fluid and see if there is an increase in rpm. This would indicate a vacuum leak.
4. - Does the carb have another port that you could run to the distrib.?

Because you say the timing doesn't change with or without vacuum I am thinking the advance unit is stuck or has a leak.

A way we used to check the movement of the plate is to remove cap, disconnect the vac line from the carb and leave it connected to the distributor. Suck on the hose and see if it pulls the plate. I know it sounds gross but that is what we used to do.

Start with these ideas and then post back.......Print Dad
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welcome tot he forum. everyone here is very helpful. it is good to have friends all over the world.

do you know if the port it is connected to is pulling vacuum? also, is it connected to the right port? some vacuum ports increase vacuum with rpm, some decrease. Take a look at the photos below for the way it is connected to my holley. not sure if the phtos attached or not. I'll try again if they didn't.
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lets try those photos again


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1964 1/2 vacuum problems ?

Thank you for all your help. Here is want I found when following your suggestions.

1- The plate that holds points moves freely.
2- Sprayed with starter fluid and had no rpm increase
3- The carb has another vac port but it is twice as large as the one I'm using for the distributor.
4- I sucked on the hose and the plates moved.

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Did you try sucking on the hose with the engine running.
The timing should advance & the rev's will increase.
If you get the cough & splutter thing, you have a distributor problem.
1964 1/2 vacuum problems ?

Well guess what ? The problem has been solved. Thanks to all of you who gave me great suggestions I found that the main problem was the gap on the points. It should be 26 1/2 to 28 1/2 and I found it to be 13. I was using my friends digital dwell meter which seemed to give an incorrect reading. I went out this afternoon and bought a good old analog meter which gave me the correct reading. Once I adjusted the idle, dwell and timing the misfiring went away.

Thanks again for all your help.

A very happy fatboy94
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Hello Fatboy 94
Nice going!!! Also thanks for posting the fix. This will help others if they come across this situation. Again nice catch. Print Dad
I know I'll have more problems down the road but I feel more comfortable knowing all of you on this forum are willing to help.

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