Cutting Out When Warm

[CatMan1]

My '28 Sport Coupe has a problem and at the end of the month we're moving 15 miles away to a new place and I don't want to have to trailer it if I can help it. The car will start decent and idle, although not sewing machine smooth. It will go through the gears and do fine for a couple miles and then when it heats up it will lose power, stumble, cut out, and backfire through the exhaust loud enough to wake the dead. Lat night I replaced the condenser, but that didn't help. I have a new coil and points to try next. I know that there are some fine rust particles in the tank, but I have the pencil screen in place. Thoughts? I'm up against the wall here for timing. I also need to make sure my '26 T will make it and my '55 Chevy truck..............

[Fullraceflathead]

If you replace the condenser with the new burnout proof condenser that should be fine if you use a Chinese made condenser that may still be your problem otherwise I would suspect the coil.

[nkaminar]

Try the new coil, but check that the fuel cap has a vent that is not clogged. Next time it happens, loosen the cap. A radiator cap on the fuel tank will not work.

[CatMan1]

Originally Posted by nkaminar

Try the new coil, but check that the fuel cap has a vent that is not clogged. Next time it happens, loosen the cap. A radiator cap on the fuel tank will not work.

I have checked the cap and it's the proper one with a pin hole vent. Maybe it needs drilled out? Maybe I should drive with the cap off? I will change out the coil next. Currently mine is upside down. Does that matter?

[CatMan1]

Originally Posted by Fullraceflathead

If you replace the condenser with the new burnout proof condenser that should be fine if you use a Chinese made condenser that may still be your problem otherwise I would suspect the coil.

Wonder how I'm to know which is which? I bought the new one from Birdhaven.

[gdmn852]

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Hello, condenser are a known issue on Model A , also check the charge rate on generator, had a 37 Ford that would go through coils, finally figured out the charge rate was too high and would overheat coil. Problem could also be coil , and unfortunately some of the replacement parts aren’t too much better. This is a good excuse to have at least 2 Model A s , take proven parts from one to check out the other,

[Y-Blockhead]

Originally Posted by gdmn852

This is a good excuse to have at least 2 Model A s , take proven parts from one to check out the other,

I'm going to use that one on my CEO next time I want to buy a Model A.

[Marshall V. Daut]

If you have one of those fuse links that bolts to the starter switch, by-pass it and run the wire directly from the engine harness to the starter switch. Then test drive the car. Those "safety" fuse links are/were poorly made with weak solder joints. When they heat up from engine temperatures, the ignition current running through the link is compromised and will cause engine misfiring. I learned this from a friend's Cabriolet I had restored for him. Once he got the car, he installed one of those fuse links and then complained that the engine would misfire upon higher speed and power demands, although the idle and driving lower speeds/RPMs were fine. I suspected the problem was the fuse link and by-passing it proved to be the answer.
Maybe the quality of these things has improved, but if you do have one and it came on an older restoration, it may be one those junk off-shore fuse links. You can either do a proper soldering job or replace it with a better quality link.
Marshall

[nkaminar]

Regarding the fuse holder that Marshall is talking about: Make sure the contacts are bright and shinny and tight on the fuse. Use a little electrical grease to keep the corrosion out.

[Mulletwagon]

Might be a bad wire connection that breaks down when it gets hot. Might check voltage to the coil when cold and when the performnce drops off. A more remote possibility is zero lash on one or more valves that prevent the valve from sealing when the engine is hot. A compression check when hot may provode some insight. Be sure and let us know what the fix is.

[Wick]

Keep things simple, you can probably just clean and check the gap and be just fine. Make sure the coil wire is tight when you put the cap back on.

[katy]

Originally Posted by CatMan1

I know that there are some fine rust particles in the tank, but I have the pencil screen in place. Thoughts?

If there's enough "fine rust particles" in the tank the pencil screen may be blocked enough to cause a fuel delivery problem.

[chap52]

I had that happen a long way from home and I loosened the gas cap and drove it for about two hours. I drilled out the vent hole in the gas cap and added an extra one. No more problem... Chap

[nkaminar]

To summarize: It appears to be a fuel problem. As others have said, remove the modern fuel filter in the fuel line. Check to make sure that you have good fuel flow to the carburetor. (Do this outside and have a fire extinguisher handy.) It should fill up a quart jar in a few seconds. Remove or loosen the gas cap and test drive.

Of course it could be an ignition problem too. Check the points and make sure all electrical connections are good, including the high tension wire from the coil to the distributor cap.

[Bob Bidonde]

These slides might help you diagnose the problem. Another hi-voltage leak can occur in the distributor cap. There is a carbon button on the cap secured in place with a brass insert. The button wears & eventually it shorts the hi-voltage to the brass insert. Also look for carbon tracks on the plastic parts in the h-voltage ignition parts. Good luck!

[CT Jack]

Dito, I think your filter is partially plugged and is allowing just enough fuel flow for starting and idling but not enough for driving. Remove your present filter and drain the tank which should help to remove the rust particles you mention. Install a standard see through filter in the line and fill the tank. If low fuel flow is your problem this fix should allow you to do your 15 mile trip.

[CatMan1]

I'm chasing a theory that came up when talking to a fellow Model A friend. This whole mess started last August when I installed a new (stock) tank valve because the old one was allowing fuel to flow past it and leak through the carb. After we put it on we got the idea that we should put one of those pencil filters in the tank on the valve. So....back out again and did that. Since that day it's been an issue. I noticed on the way to the Amanas that there was an ever so slight surging on the highway. Once we got to town it was running horrible and kept dying. I'm theorizing that there is just enough gas getting through to let it idle drive some, but once it gets warm it's not enough to keep it from boiling in the carb. It's just a thought. I'll let you know.

[Marshall V. Daut]

If you have eliminated electrical issues, you are right to move onto potential fuel problems.
I've posted this before, but it bears repeating here again. It has solved many a problem like yours. Turn off the gas tank valve. Disconnect the fuel line at the carburetor and loosen the fitting on the sediment bowl so that the fuel line can be swung around 180 degrees. Once it's at its highest point, tighten the sediment bowl fitting so that the fuel line stays in this upright position. Take off the gas cap and turn the fuel back on. Blow as hard as you can into the exposed fuel line end until you hear a strong constant gurgling inside the gas tank. That means you have blown collected gunk in the on/off valve back into the fuel supply. Unless the congealed gunk in there is really compacted, this should open up the free flow from the gas tank to the carb. Eventually the gunk will collect again in the on/off valve and start clogging it. The only solution is to remove on/off valve and drain the gas, followed by picking out the compacted crud still left inside the on/off valve.
Turn off the gas valve and reconnect the fuel line at both ends. Replace the gas cap and take the car for a test drive. The whole procedure should take about 5 minutes.
Your symptoms sound like the classic blocked on/off valve. I'll bet this solves your fuel flow problem.
Marshall

[nkaminar]

If you still have the screen in the carburetor, that could be clogged too. To test the whole fuel supply system, remove the drain plug on the bottom of the carburetor and turn on the fuel to see if you get a good steady flow out the bottom of the carburetor. Again, do this outside and with a fire extinguisher handy.

Because you got the same performance with two different carburetors, the problem is probably not in the carburetor, but upstream.

[CatMan1]

Because you got the same performance with two different carburetors, the problem is probably not in the carburetor, but upstream.



I haven't changed the carb, but I've thought about it.