I have recently got my 1940 ford coupe back on the road after years of sitting in different barns. As I have begun to work on the major know issues, as always, new ones popped up. Most of them have been easy but this most recent one had thrown me for a loop. Whenever I start it up and let it idle, it stalls out after 10 minutes like clock work. If I attempt to drive it, it also gives me about ten minutes before it stalls out. When driving it tends to buck and sputter at low rpm’s but sings at higher revs. When it stalls it takes 30 minutes for the car to fire up again. My first thought was coil and condenser. As a result I have done the following: 1)replaced coil (modern 6V with built in resistor) 2)Replaced condenser 3)Replaced and adjusted points 4)Replaced spark plugs and wires 5)Replaced both wires from distributor to coil 6)Moved coil to far side of the engine bay and flipped the coil upside down. Still after all of this, the car stalls after 10 minutes at idle and the coil is hot to the touch. It idles well during those 10 minutes and starts up easy, or at least easy for a 6 volt system. It is running a crab style distributor. Does anyone have any suggestions on what I should look at next? I am wondering if it has a resistor somewhere in the line from the ignition switch to the coil. Would that cause this issue? Do I need to replace the dash wiring harness next? Could it be a fuel issue? Fuel pump needing rebuilt? Thanks in advance from a flathead newbie!
Maybe fuel related , clogged restricted vent vac locked or maybe trash in tank being ****ed to pick up , after enigine dies it floats away . I seen these happen . Try taken gas cap off for checking Vac lock . Test if like you said clock work 30 mints Have a can brake clean , When @ idle engine goes to Die spray with taps of brake clean into / over carb "mist" without air cleaner & see if able to keep running , if so then you narrowed it down to fuel issue and supply
Well, I won't claim to be an expert in 6V points ignition, but a few things make me wonder... First, a 6V coil 'with resistor'. AFAIK, most 6V ignitions don't use a resistor, they're generally used on 12V systems to reduce the voltage to 6V. Inadequate voltage could explain the bucking at low speeds. Second, dwell degrees. You'll need a dwell meter to check this. Excessive dwell will contribute to coil heating, particularly at slower speeds. And idling is the worse-case scenario for coil heating. Excessively worn lobes on the points cam or incorrect point gap can cause this. And I would look at the fuel system. Disconnect the fuel line from the tank at both ends and blow some high-pressure air through it. Tie a rag around the exit end to see what comes out if anything. You may have a partial blockage.
After sitting in storage for years I initially thought you might have some sticking lifters or valves. But running the engine at temperature with fresh oil would maybe alleviate the problem, and not make it worse. But then I started wondering if it might have the valve lash set just a skosh too tight. Worked on a Dodge flathead 6 years ago with symptoms similar to yours. I ran the valve lash and adjusted everything maybe .002" to .003" looser than published specs and it cured the stalling issue. And it started much easier at higher temps. Picked up just a slight increase in tappet noise when cold started but it was a small price to pay. Do a cranking compression test with a cold engine, all plugs removed and throttle held open. Then reinstall the plugs, allow the throttle to close properly and restart the engine. Let it run until it stalls out and remove the plugs again and do another cranking compression test while the engine is still hot. If a few cylinders show markedly lower pressure readings it may be the result of a few valves not closing fully. At operating temps with the expansion of parts due to the heat the valvetrain may now have zero lash and the valves aren't able to fully seat. You may also notice some random back firing in the intake manifold and/or the exhaust. You might also be able to spot the problem by doing a cranking vacuum test. It's a simple test and there's plenty of online sources that explain the procedure. A low reading could result from the intake valves not sealing fully. If you don't already own a vacuum gauge this might be a good reason to invest in one.
I have replaced the fuel tank and lines because of the fact that it sat so long. But I will try the Brake cleaner and fuel cap test to rule out any fuel system related issues.
When it stalls out, pull the coil wire out of the distributor cap and hold it about a quarter inch from the block. Have someone crank the starter. If you have a spark, you probably have a fuel problem. If you do not have a spark, you have an ignition problem. Simple test.
How is gas tank vented? Gas cap Top of tank vent. Try running it with no gas cap to see if that solves stalling issue.
Sounds like a heat related ignition problem to me. An overheating coil can malfunction until it cools down again. This would happen pretty much "like clockwork". Check how much voltage your alternator is pumping out.
I would get a standard coil and run an external resistor. Sounds like that internal resistor is overheating the coil.
I'm liking the clogged fuel vent hypothesis. I had this happen to my motorcycle with a new defective cap. Very confusing as the fuller the tank is the shorter the run time. Less air in the tank means more vacuum per volume of fuel removed.
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