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MarkV

1940's V-8 Issue

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On my '48 Lincoln with a 1951 Merc. Flathead V-8 I have developed a strange issue which has prevented me driving it. I can drive around for say 15 minutes, then when I put a little stress on the motor the car dies. It will then restart about 45 minutes later. I have replaced the coil, condensor and points. The carb. is newer and the fuel pump is just a couple years old. The ignition wiring is new and the wires to the spark plus are newer too. The car will idle all day long. This is the strangest thing! The car was NEVER like this before.

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Guest BillP

Keep swapping out coil and condenser until it's resolved. Even new ones go bad. That's my first thought.

Second thought is drain all gas, blow out line backwards and forwards, put in a new filter and fresh gas.

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It would be helpful if you could narrow it down to fuel or ignition. When the failure occurs, see if you can get the engine to restart with a squirt bottle of gasoline or a can of starter fluid. Or conversely, by cranking the engine and seeing what kind of spark you have.

One notorious failure on these engines: the fuel pump lobe on the camshaft would go flat, allowing the fuel pump to deliver just enough fuel to idle, then starve under a slight load once things get warm. Fuel pump pushrod travel should be .200 in.

However, sounds more like an ignition problem -- coil, condenser, cap -- but long-distance Internet diagnosis can be fraught.

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another idea is what I discover when I had a 1968 Eldorado, it would run for awhile, then die and would not start again for awhile. turned out to be a bad gas cap that stop venting the gas tank, after a little driving, the vacuum pressure created in the gas tank became more negative pressure than the fuel pump could over come. I took an ice pick and punch a single vent hole through the gas cap, problem solved. Charles Coker, 1953 Pontiac tech advisor.

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Sounds to me like a piece of crud in the gas line thAT GETS DRAWN UP TO A TIGHT SPOT AND RESTRICTS THE FLOW. tHEN WHEN THE SUCTION SUBSIDES IT FALLS LOOSE. i HAD THIS HAPPEN ON A '41 fORD, A TINY PEBBLE WOULD LODGE AT THE PUMP FLEX LINE CONNECTION . i CHANGED A BUNCH OF FUEL PUMPS BEFORE THE PEBBLE FINALLY STAYED STUCK IN PLACE AND WAS DETECTED. GOOD LUCK.

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Put a T in the fuel line near the carburetttor,,and connect a pressure guage,,,

now you will know,,avoids guessing,,I think i recall a compound gauge that

would measure both vacuum and pressure,,// Manifold vacuum

Cheers,,Ben

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IF your mechanical valves are not closing all the way, The engine will start fine and run for a while but loose power and die when the engine slows down like on an exit ramp. My initial fix was to increase the idle. What happens is the valve stem gets hot and expands leaving the valve open when it should closed. Check the compression on all 12 cylendars for a low number both when the engine is cold & again after 15 minutes. I had the problem and had a shop do an "ENGINE CHECK" to identify if the leakage was in the intake, exhaust valve, or ring is leaking. On a 6 cyl, I didn't have a real problem until the 2nd cyl was leaking. Readjusting the exhaust valves fixed the problem.

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Next time it quits jump out quick and check for spark and gas. If you carry a spare coil and condenser you may be able to fix it on the spot.

Here is a hint. The condenser does not have to be inside the distributor. It can go on the coil. If you have a spare condenser of the correct value, or even close ( + or - 20% is considered good) you can attach it to the coil and hook it up if you need it.

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From my younger years, a ping pong ball in the gas tank will give these exact symptoms! Only on older cars with no tank filter. Not sure how I learned this!

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Ping pong balls or even a bead of solder rolling around in the tank that broke loose 40 yrs after it was manufactured. Fuel blockages can be very baffling until you find them. Also had an insect cocoon stuck in a fuel line once. Previous owner had circumvented the issue with an electric pump and a rubber line to the carb. I found out the mechanical pump was just fine after I blew the cocoon out of the steel line.

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There is always a chance of vapor lock if you have a fuel line running too close to the manifold. After the fuel cools, it will flow and let the engine run until it gets hot enough to vaporize again. Was very common on the old flatheads when we were kids in the fifties.

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Sounds to me like a piece of crud in the gas line thAT GETS DRAWN UP TO A TIGHT SPOT AND RESTRICTS THE FLOW. tHEN WHEN THE SUCTION SUBSIDES IT FALLS LOOSE. i HAD THIS HAPPEN ON A '41 fORD, A TINY PEBBLE WOULD LODGE AT THE PUMP FLEX LINE CONNECTION . i CHANGED A BUNCH OF FUEL PUMPS BEFORE THE PEBBLE FINALLY STAYED STUCK IN PLACE AND WAS DETECTED. GOOD LUCK.

I had this same problem once in an old jeep. But the pebble was in the hard line at a connection mid frame.

Dont remember just how I tracked it down, but I remember it was a HUGE relief when I did.

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