1972 351c 2v, intermediate start/rough running

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Jaysay

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Hey this is my first post on this forum, I’ve posted this issue in another and they’ve helped but it’s been several weeks and ideas are starting to run thin. I’ll list off everything I can remember doing an confirmed is correct.

I have a 72 mustang with a 351c 2v project that was my fathers, he bought it back in 73 and it sat in a shed for about 25years after he swapped vehicles. Did some work on it about 8years ago an got it running, then it went back in the shed until earlier this year when i moved it to my own house. It has 93,000miles with a very detailed book of everything he’s done to it. Since i began work again i got it running with a new fuel tank an deep carb cleaning. Ran great and was doing general maintenance on it getting it road ready. Until one day it just decided it didn’t want to start. It would crank strong and when it would start it would run very rough almost shaking, then die. The following is everything i can think of that’s been done to it:
Carb Rebuild, fuel tank, fuel lines, fuel filters
Spark Plugs, wires, points, condenser
Oil, antifreeze, water pump, coolant lines
Vacuum lines, starter an solenoid.

Things I’ve checked:
2.Carb was cleaned several times very well
3.Checked for Vacuum Leaks
4.Pulled distributor and checked for correct placement, it is set at #1cyl TDC.
5.I have initial timing set to 12 degrees, it was 6degrees but was told most like them advanced more and it did like it.
6.Points gap checked an confirmed at .17 (might confirm that’s in the ballpark)

Feel like I’m forgetting a few things still. But the issue has been intermediate. Yesterday is when i pulled the distributor an checked for correct placement, after getting everything set up, the car fired up immediately with no issue. I let it warm up, then played with the initial timing. Got it sounding great, ran incredibly smooth and advancing it really helped. After that, i went out a little while later to reconfirm timing and finish putting stuff back together, ran great at that time too. Then an hour after that, went to check dwell and idle speed, an it went right back to hard starting. It sounds like it has no fire, but if i give it half throttle it’ll kind of start to pick up an sometimes it’ll start with no throttle but run rough. And then if i leave it be for a day or so, it might be the same or it might fire up like it never had an issue. That’s what throws me off the most, and has me leaning towards electrical. Sorry for the long post, but wanted to get all the info i could to you. Thanks in advance for any advice you might have.

Also, forgot to add that when it starts an runs good, i can rev it, make adjustments and probably let it sit an run until the fuel tank is empty. Never has any issue once it’s running right, only happens randomly after shutting it off.
 
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mjseakan

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Just a wild guess: hairline crack in the distributor cap?

And welcome to the site, someone here will come up with the answer I'm sure.
Mike
 

Jaysay

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Just a wild guess: hairline crack in the distributor cap?

And welcome to the site, someone here will come up with the answer I'm sure.
Mike
Thanks! I’ve looked the cap over, but I’ll check it again to be sure. Might have a used one somewhere that i can test with.
 

rvrtrash

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I'd also check for movement in the distributor shaft while you have the cap off. If the shaft bushings are worn, your dwell angle will be all over the place. If you have a dwell meter, that's the best way to see what the actual dwell is.

Steve
 

Hemikiller

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I've responded to your post over on the VMF as well.

Can you post a good overview pic of the battery wiring? My thought is you're having an intermittent ground issue. The factory ground cable has a ground strap midway that is supposed to be screwed down under the voltage regulator screw. It is often missing on aftermarket cables, or just not bolted down. From experience, if that's missing, it'll cause the problem you are having.
 

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Sheriff41

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Just brainstorming here:

You might try backing the timing off a couple degrees.

Is the fuel line from the pump to the carb routed so it is not touching the engine? You may be getting some vapor lock if the fuel line is too close to the engine.

After sitting for so long, if it has the original nylon timing gear it may be failing.

Check the fuel filter again. When you say fuel lines do you mean you replaced the hard lines from the tank to the fuel pump? Did you replace the fuel pump?
 

Jaysay

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Rvrtrash- Shaft has a little play, may need to address that soon, but the dwell angle stays steady at about 27degrees with very little fluctuation.

Idaho Chris- I have 2 condensers, 1 of them new an testing with a multi meter both seem to be good. I’ve swapped back and forth with no change.

HemiKiller- I’ll see about getting that pic of wiring posted today, don’t think battery cables have been swapped from factory, but may need to be due to age.

Sheriff41- I replaced all fuel line, tank to pump and pump to carb, it’s routed so it dosnt touch, but is close to the engine. Pump was never replaced though, i have an electric pump I’ve had set aside that i should probably install. Also, according to records my dad replaced the timing gear and chain at 64,000 miles.
 

CarCrazy73

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Actually I have a '71 fastback (M code, 1F interior code, V exterior code paint); a '73 Grande' (Q code, 6E code exterior paint; FF code interior) all original, owned since new, original paint, vinyl top, interior, engine has never been opened up and a '73 convertible (Was an H code) (3B code exterior paint; CB code interior) currently restomoding her.
[url=https://ibb.co/LhxRfvz][img]https://i.ibb.co/Tq425rB/B91092-E3-2-DB3-4-B69-95-F3-F192-B3-CECD6-C.jpg[/img][/url]

[url=https://ibb.co/jMc3qp0][img]https://i.ibb.co/BZXTv1W/IMG-1813.jpg[/img][/url]
I have a ‘73 with the same power train. Mind started doing this a few years ago. It turned out to be in the distributor. Mine had a little plastic pin that the advance plate sits on. It broke apart due to age as it is the original distributor unit. I finally towed my car to a garage where I live that lives working on all the old pre-80’s autos. He went right to the source. We were able to find the piece(new), repaired and she been running great since. This missing, choking effect as you mentioned was what I was experiencing. She would start right up, run good one time, next time missing, choking off, you name it, it was doing it. Just an idea.
 
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73 Grande will undergo three phase build process. Phase 1 is to make roadworthy. Phase 2 is interior/exterior restoration. Phase 3 is ++ performance.
Because it seems the rough idle/off idle is sporadic, I would tend to think it’s the fuel system. Carcrazy73 may be right if that pin is missing. You haven’t mentioned what carb you are running. If it’s not too difficult, you might check to ensure there isn’t anything in the float bowl, creating a restriction. Since everything seems to have been clean, and most of the system parts are new, it might be a long-shot. I hope you’re able to solve the problem, sounds like a great car.
 
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There is something wrong with either the carb or the electrical system/distributor, and I would bet that if it sometimes runs great that the distributor or the electrical system is the issue. Usually a carburetor issue is always there. Check the grounds to the engine, make sure that you have good ground, you could make a supplemental engine ground just to make sure. Check the coil, it could be going bad. Check the wire going from the points to the negative side of the coil, make sure that it is not grounding itself or that there is an internal short on it. When you have issues with the engine not starting check the + side of the coil and see what voltage you have there, with points there is a resistance somewhere and you should have about 9V, if it is less than 9V or more you have an issue. Check the advance plate on the distributor, make sure that it is moving smoothly and that it is not getting stuck.

As for the carb, a lot of carburetor issues can be diagnosed with the air cleaner off and the engine running. You could have a float that occasionally sticks, when it does the fuel just drips down the carb boosters and just floods the engine. A piece of debris may be stuck on the needle and seat on the carb, usually happens when you work with rubber lines, and a small piece of the rubber line just breaks off of shears off and gets itself stuck on the needle and seat. When the engine is not running well, take the air cleaner off and look down the carburetor. See if you can see fuel dripping out of the boosters, you should see no fuel dripping into the engine at idle, all the fuel is coming in under the throttle blades through the idle circuit and you cannot see it. A piece of debris, usually rubber hose, can go into the carb and float around inside the bowl and give you headaches. It can go onto a main jet and block it or partially block it. when I have seen this the car usually idles well, but when you get off the idle circuit, it runs horribly as one side of the carb is running way lean. If you have a blocked jet you will see it when you accelerate the car in neutral and look down the carb, one of the booster will be flowing a lot more fuel than the other, it will be quite noticeable. Please be careful when looking down the carb with the engine running, especially an engine that is not running well. It can backfire and burn off you eyelashes, ask me how I know...

The only other thing that I can think off would be the timing chain. Stock timing chains have nylon teeth and they wear out. I have never had this issue personally, but I do know that they can wreak havock when they are about to let loose and the chain is all stretched out.
 

Jaysay

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Like to thank y’all for all the advice and info up to now. I’m kicking myself right now…I won’t say i found the issue YET, because each time i say that it proves me wrong. I started the car up before work, ran it a little bit an shut it down. Took a quick look at the carb an with some better light I could see gas actually draining down from the area around the Venturi Booster. By the time i got back the fuel bowl had drained to half it’s normal level before it stopped leaking. I must’ve damaged that gasket during install, I really should’ve caught that sooner, but I’ll get another gasket kit ordered in an hope that’s it.
 

c9zx

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It may be fuel percolation after shut down when the carb and intake become heat soaked. The fuel boils and comes out of the venturi boosters and into the intake, essentially flooding the engine with fuel. So when you try to start it again it doesn't want to start and runs poorly. Make sure the float level is correct and a heat isolation gasket is between the carb and the intake. I hope you get it figured out. Chuck
 
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Like to thank y’all for all the advice and info up to now. I’m kicking myself right now…I won’t say i found the issue YET, because each time i say that it proves me wrong. I started the car up before work, ran it a little bit an shut it down. Took a quick look at the carb an with some better light I could see gas actually draining down from the area around the Venturi Booster. By the time i got back the fuel bowl had drained to half it’s normal level before it stopped leaking. I must’ve damaged that gasket during install, I really should’ve caught that sooner, but I’ll get another gasket kit ordered in an hope that’s it.
What type of carburetor are you running? Usually when you get a fuel leak at the boosters there are no gaskets involved in the leak. You either have a needle and seat that is not closing correctly, you have a float that has fuel in it and is sinking, or the float level is just too high to the point that the needle and seat never close. I am a Holley guy, but I have worked with Carter carbs and Rochesters and I don't think that this could be a gasket in the carburetor. Usually gaskets in most carburetors are above the fuel level, except on Holleys, and by the time you have fuel all the way to the gasket level, it is just easier for it to just flow out of the boosters than it is to seep out of the gasket. On Holley carbs, no matter how bad a gasket is, fuel can leak out of the carb onto the intake manifold, but not into the carb.
 

Jaysay

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What type of carburetor are you running? Usually when you get a fuel leak at the boosters there are no gaskets involved in the leak. You either have a needle and seat that is not closing correctly, you have a float that has fuel in it and is sinking, or the float level is just too high to the point that the needle and seat never close. I am a Holley guy, but I have worked with Carter carbs and Rochesters and I don't think that this could be a gasket in the carburetor. Usually gaskets in most carburetors are above the fuel level, except on Holleys, and by the time you have fuel all the way to the gasket level, it is just easier for it to just flow out of the boosters than it is to seep out of the gasket. On Holley carbs, no matter how bad a gasket is, fuel can leak out of the carb onto the intake manifold, but not into the carb.
The carb is a Motorcraft 2100-D. I’m not sure if the gasket is the issue, havnt had a chance to take it apart, but you’re right that it may not be a gasket. I’ll try looking at the float level this week and check what c9zx suggested earlier. Maybe the power valve? Put a new one from the rebuild kit in, but it wasn’t identical to the old one, holes in it were a bit different style.
 

mjlan

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Fuel leaking into the intake could be causing you problems. Now figuring out why will probably be a challenge. If you haven't been in the carb the gaskets could be dried out/ messed up. Also I will throw out there that current fuel formulations behave differently than those in use at the time when these fuel systems were originally designed. Two things that come to mind that may be affecting you are the lowered boiling point of the fuel due to the alcohol being added and that alcohol affecting the carburetor and its gaskets.
 

Fabrice

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As @Hemikiller said, I'd look at these battery cables first.
I'd also after your batt is recharged, try start and then right away measure the volts at the poles. Older batts are often going low on volts right after the first discharge and while you think it's +-12.6, it's actually more like 10.5 to 11 or lower.
 
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You could have a bad power valve, but that would not make it leak through the boosters where you can see it. When you have a broken power valve the fuel will go directly into the intake manifold from underneath the carburetor. If it it leaking through the boosters, it means that the fuel bowl area inside the carburetor is completely filling up with fuel, and when that happens the fuel needs to go somewhere, and that somewhere is out your boosters. So, you probably have the 3 options I outlined earlier with either the needle and seat, float level, or a bad float.
 

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Get a fuel pressure regulator, set up to 6lbs, check the needle/seat assembly. Make sure you have a good fuel filter. Any tiny spec of dirt can hold the needle open. Carbs cab be very sensitive to fuel level In the bowl. Too much fuel in the bowl can make the circuit run rich. I'm not familiar with that model carb, but I'm good with holleys and edelbrock stuff. Most of them operate basically the same.
 

Don C

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A common mistake on replacing power valves is overtightening them and distorting the gasket, allowing fuel to leak into the intake manifold. Other things I would check have already been mentioned.
 
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