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1966 Ford Mustang 289
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Discussion Starter · #1 ·
Hey all, I'm new here and hope this is the right place to ask for advice. I bought a 1966 Mustang Coupe with a 289 and 2 barrel carb. Since the day I bought this car 3 months ago I have not been able to go over 50 MPH without it giving me problems. Once it hits 50MPH it will start bogging down and hesitating, sometimes it just dies. BUT it will start right back up with no problems. I can idle and Rev the engine as high as I want with no issues. I was thinking it was fuel related so I replaced the following (not in order) -fuel pump, fuel filter, fuel tank, and sending unit. I also cleaned the fuel lines. None of this worked. I replaced the whole carb with everything on it, didn't work. I have also replaced the dist. cap, spark plugs, spark plug wires, ignition coil, battery, and ignition module. Still not working. I have had a few local mechanics who do well at their jobs look at it and it still isn't running. Please help if you can.
Thanks!
 

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There are a lot of possibilities here, but without hearing/testing it with you, it's a little hard to guess. Just to help you troubleshoot, here's what I'd do.

Electrical is usually the 'easiest' to troubleshoot, and also the most likely source of the problem. Pull your spark plugs and look at them, one at a time. Are they all about the same? If not, you can tell which cylinders have a problem, and figure out why. Each one will tell a story. Ideally, the insulator should be light tan, the electrodes should have nice clean edges, and may have a little soot on them, but not 'furry' with soot (running too rich or timing too retarded) ashy (oil fouled), and not wet (fuel fouled) or oily. If the electrodes look burnt (melty or bright 'hot metal' colors), or the insulators are really bright white (or chipped), that indicates your ignition is too advanced, and/or you're running lean. With old style straight gas and no alcohol, they would smell faintly of toast. (not even kidding)

If they're not good, change 'em out and move on to the next electrical thing - which, since you've done all the parts (and hopefully they're good!) should probably be timing. Just to be on the safe side, check to make sure your wires aren't arcing when the engine's running. It's really easy to see at night, but you can also visually inspect the wires for small black spots where they have blown through the insulation. After that, you will want to verify that the damper and its marks are accurate. The 'easy' way to do that is find Top Dead Center by pulling the #1 spark plug, and then use a dowel or something similar that can't fall down inside the hole, or mar your piston. Turning the crank by hand (a big socket is helpful) you can find exactly where it reaches the top of its travel, watching the dowel move in and out of the spark plug hole. You can also buy a piston stop that screws into the spark plug socket and uses a screw, but the main thing is to make sure your timing marks match the reality of your crank's position.

Once you know that the weight on your damper hasn't slipped, and the pointer lines up with "0", you can set your car's timing accurately. There are lots of posts about doing this, but the short version is: 8-12 degrees of timing at idle with your vacuum advance disconnected, plugged, and engine warm. The timing light should show your timing advance to about 2800 rpms as you gently rev the engine, then stop, and it should wind up around 32-36 degrees total mechanical advance. Hook up your vacuum advance again when you're done, and your idle will smooth out dramatically, allowing you to set your idle speed down around 650-700 or so with an automatic when it's in Drive and your foot's on the brake. If you are running points, be sure to check the points gap, and make sure there's enough dwell. Without enough time 'closed' or 'open', the ignition system will not have time to fully charge up for the next spark before it's firing. Definitely a "Goldilocks" scenario. Since old-school matchbooks aren't that easy to come by these days, a feeler gauge may be in order to figure out if you've got the right gap for your points.

When you've got the timing right, you can begin to look at carburetor/fuel issues. If your car idles smoothly, you can rule out problems with vacuum leaks, as your problem isn't happening at closed-throttle operation anyway. That leaves issues with your main circuits in the carb. Modern gas has ethanol in it, and that stuff is horrible for carburetors, especially if they're allowed to sit for any length of time. It corrodes the aluminum and leaves weird crystalline deposits that clog everything up. It also embrittles rubber seals and pumps, which causes leaks and malfunctions. If you have an original Autolite carb, it's easy to take the top off and look to see if you have problems with that kind of thing. If it's all gummed up, you will have to make a judgment call about whether the damage is slight enough that you can rebuild it, or if you'll need a new one.

If none of this improves your car (and I would be surprised if that's the case!) you may have a more serious mechanical problem with your engine, like valve recession. You can do a compression test to find out if there is an issue with your rings, pistons, or valves. Hopefully, it's already running great by this point, so it's not something you have to worry about.

Hope this helps!
 

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I would check the vacume advance...... the diaphram might very well be shot or the float level in the carb is too low
 

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1966 Ford Mustang 289
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Discussion Starter · #5 ·
There are a lot of possibilities here, but without hearing/testing it with you, it's a little hard to guess. Just to help you troubleshoot, here's what I'd do.

Electrical is usually the 'easiest' to troubleshoot, and also the most likely source of the problem. Pull your spark plugs and look at them, one at a time. Are they all about the same? If not, you can tell which cylinders have a problem, and figure out why. Each one will tell a story. Ideally, the insulator should be light tan, the electrodes should have nice clean edges, and may have a little soot on them, but not 'furry' with soot (running too rich or timing too retarded) ashy (oil fouled), and not wet (fuel fouled) or oily. If the electrodes look burnt (melty or bright 'hot metal' colors), or the insulators are really bright white (or chipped), that indicates your ignition is too advanced, and/or you're running lean. With old style straight gas and no alcohol, they would smell faintly of toast. (not even kidding)

If they're not good, change 'em out and move on to the next electrical thing - which, since you've done all the parts (and hopefully they're good!) should probably be timing. Just to be on the safe side, check to make sure your wires aren't arcing when the engine's running. It's really easy to see at night, but you can also visually inspect the wires for small black spots where they have blown through the insulation. After that, you will want to verify that the damper and its marks are accurate. The 'easy' way to do that is find Top Dead Center by pulling the #1 spark plug, and then use a dowel or something similar that can't fall down inside the hole, or mar your piston. Turning the crank by hand (a big socket is helpful) you can find exactly where it reaches the top of its travel, watching the dowel move in and out of the spark plug hole. You can also buy a piston stop that screws into the spark plug socket and uses a screw, but the main thing is to make sure your timing marks match the reality of your crank's position.

Once you know that the weight on your damper hasn't slipped, and the pointer lines up with "0", you can set your car's timing accurately. There are lots of posts about doing this, but the short version is: 8-12 degrees of timing at idle with your vacuum advance disconnected, plugged, and engine warm. The timing light should show your timing advance to about 2800 rpms as you gently rev the engine, then stop, and it should wind up around 32-36 degrees total mechanical advance. Hook up your vacuum advance again when you're done, and your idle will smooth out dramatically, allowing you to set your idle speed down around 650-700 or so with an automatic when it's in Drive and your foot's on the brake. If you are running points, be sure to check the points gap, and make sure there's enough dwell. Without enough time 'closed' or 'open', the ignition system will not have time to fully charge up for the next spark before it's firing. Definitely a "Goldilocks" scenario. Since old-school matchbooks aren't that easy to come by these days, a feeler gauge may be in order to figure out if you've got the right gap for your points.

When you've got the timing right, you can begin to look at carburetor/fuel issues. If your car idles smoothly, you can rule out problems with vacuum leaks, as your problem isn't happening at closed-throttle operation anyway. That leaves issues with your main circuits in the carb. Modern gas has ethanol in it, and that stuff is horrible for carburetors, especially if they're allowed to sit for any length of time. It corrodes the aluminum and leaves weird crystalline deposits that clog everything up. It also embrittles rubber seals and pumps, which causes leaks and malfunctions. If you have an original Autolite carb, it's easy to take the top off and look to see if you have problems with that kind of thing. If it's all gummed up, you will have to make a judgment call about whether the damage is slight enough that you can rebuild it, or if you'll need a new one.

If none of this improves your car (and I would be surprised if that's the case!) you may have a more serious mechanical problem with your engine, like valve recession. You can do a compression test to find out if there is an issue with your rings, pistons, or valves. Hopefully, it's already running great by this point, so it's not something you have to worry about.

Hope this helps!
Thank you so much for all of the great advice. I will be working on all of this after work on Friday and this gives me hope. I will update as soon as possible. I really do appreciate you taking this time to explain in detail what may be wrong. Kudos for suggesting things no mechanic has even mentioned to me!
 

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Thank you so much for all of the great advice. I will be working on all of this after work on Friday and this gives me hope. I will update as soon as possible. I really do appreciate you taking this time to explain in detail what may be wrong. Kudos for suggesting things no mechanic has even mentioned to me!
Just to be fair, a lot of mechanics working now have never seen a distributor with points, or a 60s carburetor! Once you understand 'em, they're really not so bad - but trying to figure out how they work without any experience is a bit of a stretch. They probably don't even have shop manuals for cars like ours in most shops any more.

If you don't have the Ford shop manual for your car, you really should get it! You will be amazed at how nice it is for helping you troubleshoot common problems, and walking you through things step by step. Definitely worth the money.

Also - forgot to say welcome to AFM!
 

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1966 Ford Mustang 289
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Discussion Starter · #7 ·
Just to be fair, a lot of mechanics working now have never seen a distributor with points, or a 60s carburetor! Once you understand 'em, they're really not so bad - but trying to figure out how they work without any experience is a bit of a stretch. They probably don't even have shop manuals for cars like ours in most shops any more.

If you don't have the Ford shop manual for your car, you really should get it! You will be amazed at how nice it is for helping you troubleshoot common problems, and walking you through things step by step. Definitely worth the money.

Also - forgot to say welcome to AFM!
You hit the nail on the head here about most of these mechanics. I am in my 20s and never have dealt with what you have mentioned either, but I have been lucky enough to buy my dream car. I am trying to learn everything about it and honestly with all the issues it has given me, it has taught me quite a bit already. I'll look into the manual right now. Thanks again!
 

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hey Just a note on Vacuum Advance....I just went thru replacing one of those but it's on a old Flathead V8 engine but still would be same for your Mustang.
If you have a vacuum pump (like a 1 man brake bleeder tool) you can put a little vacuum on the diaphragm and see if it holds. In my case the bad one held NO vacuum, the pumping of the vac pump just wiggled the needle.
Once I got a new one to test on, the vac pump needle registered vacuum and held it with a very slight leak down.
Don't pump it up too high, dont want to damage the new diaphragm, but see if it will hold vacuum, you'll see the difference once you know you have a good one vs a bad one.

Made a big difference on how the engine ran, I've got power now under acceleration like I never had before.
Unfortunately in my case I also discovered a transmission issue with it (bad bearing I believe) so I'll be distracted from more tuning but I had no
idea how the vac advance can affect the engine tune until I went thru this process.

Also with the truck I didn't have some key information like points gap, dwell, timing settings so i had to do some testing to find what worked.
After all that THEN my shop manual arrived! lol
here's the link to that thread on the FTE site if you wish to view it, maybe it'll help. Not a lot of pictures but I try to be descriptive.
Flathead V8 vacuum advance canister test and replace - Ford Truck Enthusiasts Forums
Hope it helps!
T
 

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Discussion Starter · #9 ·
I am completely lost at this point. Everything but the distributor itself and anything inside the engine haven't been replaced yet. My mechanic says it has to be internal. If we look at this problem from an internal aspect what do you all think it could be? We did a fuel pressure test and it was testing at 3.5 then dropping to zero a mile down the road. We went and installed a holley electric pump to see if that was the fix and that pumped much stronger, but I am still stalling often. Also another note, my brand new ignition coil cracked in the front and was leaking.. I feel we are so close to the fix, but so far at the same time. Thanks for your time and help guys.
 

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No where in this thread do I see what your timing and dwell settings are? What RPM is it idling at? Do you have A/C? Is it an automatic or standard? What temperatures is the engine reaching at cruise speed and extended idle?
 

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Fuel pressure with a carb will typically go from 'normal' to 'zero' (or very low) as you're moving, because the floats open up the needle valves and release line pressure. So that in itself is not cause for concern.

If you want to rule out 'internal problems' (and honestly, it doesn't sound like that's your issue!) you can do a compression test.

Can you describe how it's malfunctioning? Just a serious lack of power, or is it stumbling and coughing? Does it run great till you give it too much throttle? Does it run WOT great for a moment, and then fall on its face (fuel starvation)?

Even if a part is replaced, it doesn't mean it's hooked up right, adjusted properly, or even working! (your coil is a great example, sadly)

With that getting so hot, and cracking open, I wonder if your ignition system is the issue here, more than ever. Too much voltage (someone removed the resistor wire) can mean that your coil runs hot and malfunctions over and over. What kind of distributor do you have?
 
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