I am putting a 57 Thunderbird back in use after 15 years in storage. This was a rotisery restoration 25 years ago and we have replaced a lot. It won’t run when after about 15 minutes of running. Starts hard, idles rough, engine shakes, gets worse and worse until it eventually stops. New fuel pump, fresh professional rebuild on carb. new coil and resistor. Checked fuel lines for being to close to engine. Choke is off when it stops (not a choke problem). What shall I do next.
Drop the fuel tank.
Tester
Fuel tank is brand new.
When was the new fuel tank installed?
Tester
Last week.
Im thinking fuel also but I don’t understand why it take 15 minutes to get worse and worse until it stops. Then you can’t start it again until its cool.
Maybe vapor lock?
Tester
I dont know much about vapor lock. How do I check for that? Thanks.
Run the engine until it dies.
Pour cold water on the fuel line from the fuel pump to the carburetor.
If the engine starts, that’s vapor lock.
Tester
Ok, I’ll do that in the morning. And report back. Lines are not very close to the block or heads, but I will do as you say. Thanks much.
That carburetor is leaking, fresh rebuild or not.
Leaking vacuum or leaking gas?
Coincidentally I had a similar problem on my early 70’s carb’d Ford truck, 302, developed just recently. It would start, run & idle fine, drive here, drive there, 65 mph, ok for 10 minutes, then almost like a switch had been thrown, it would start to buck, refuse to accelerate past 35 mph, and eventually stall completely. The weird thing, once it stalled it would immediately start back up and run ok for another 10 minutes, when all the problems would come back as before. That turned out to be a defective carburetor power valve. I expect your problem has something to do with the carburetor and/or something that is supposed to be holding vacuum isn’t. I’d start by a basic vacuum check, and if that didn’t root the problem out, remove the carb for a look see at the float/inlet valve, and spray the passages with a can of carb cleaner, check the power valve’s diaphragm hasn’t become incontinent (if your engine sports a power valve) . All this is not overly difficult and should provide some clues to what’s wrong anyway.
Another possibility is the ignition system. Check for a good healthy blue-white spark at the tip of spark plug during cranking. Ignition system problems usually result in complete stalls and cranks-but-won’t-start, so given your symptoms I’m still leaning toward the carb idea above.
The fuel delivery system (fuel pump etc) require the tubes between the tank and the carburetor be 100% filled with liquid fuel. If something causes the fuel to boil inside a fuel line, this turns it into a gas rather than a liquid. This pertains to the carburetor itself as well. There’s usually a spacer between the carb and the intake manifold which helps isolate the heat of the engine from the carb’s base. Make sure that carb/intake manifold interface is the same as it came from the factory.
Doesn’t sound like it’s running long enough for vapor lock, especially in the middle of winter. Did it run fine before it went into storage? If it did, then it’s not vapor lock, unless its being caused by a weak fuel pump.
Ignition condenser ?
1 Like
I like the power valve in the carb where ever that is since it sounds like fuel. When it stalls though, check for spark with a spark tester or spare spark plug. If spark, then it’s a fuel problem.
Compression test would be my next step.
We are working on this now. But I wanted to toss this one at you because it may be a related clue. When the motor is running, there is an intermittent buzz coming out of the radio speaker. The radio is off. It does not seem to raise and lower with RPM but it does change at times. Seems crazy to me. Any ideas on that one? I appreciate all this help.
Your speaker issue sounds mechanical, since it’s happening with the radio off. I’ll bet the speaker cone is rotted around the circumference where it attaches to the speaker frame.