Losing power when warmed up

[rugreen]

Does it start easily when you first crank it up to go for a drive?
Does it run good, pull hills, etc. until you have to stop or slow down for traffic?

As eagle said...check the point gap for sure and while you're at it, check the timing and maybe have your mechanic friend check the timing gear to see if it might have jumped time. It's possible that the coil might be faulty, so replace it with a known good one. Condensers are a common failure item - cheap and easy to replace. Buy a good one like one of the "no burnout types" from Bratton's, Snyder's, etc.

Yes, the truck starts fine and drives fine. The only time I have the issue is if I take a long drive on hilly roads and then come to a stop or slow down due to traffic. Even in this case, it idles fine, but has a complete loss of power. I will check the point gap and will ask my friend to look at the timing (I'm having other issues with the transmission and am hoping to get it down to his shop to look at it).

 

[rugreen]

Since you have the 30 Coupe that is running well and if a new condenser doesn't help try using the carburetor and distributor on the pickup. One at a time.

Another thing comes to mind is it possible you have an issue in the muffler that is causing back pressure when it heats up?

Yes, this is the general approach that I'll take; I started with the coil ... my fear though is that I'll do something that will result in both vehicles not running

 

[Mulletwagon]

If everything else checks out might check for insufficient valve lash (if equipped with adjustable lifters). Interesting problem, please share the fix.

 

[rugreen]

Hey,

What about fuel evaporating in the fuel line?? Is that a thing with the Model A's??

I seem to recall some talk about that a while ago.. It would make sense to me if you are pushing it hard on the mountain roads and the fuel sitting in the fuel line close to the exhaust.. If you stop or just idle, the fuel will sit in that hot spot a lot longer than open throttle..

Just a thought..

Thanks. I read a long thread on vaper lock and Model A's because I thought this might be the issue. Although true vapor lock only occurs if you have a fuel pump, others have commented that they get a vapor pocket form in the carburetor that prevents proper flow of gas. They mentioned loosening a bolt on the top of the carb above the bowl when this happens to release the vapor bubble. I will see if this works.

 

[rugreen]

If everything else checks out might check for insufficient valve lash (if equipped with adjustable lifters). Interesting problem, please share the fix.

Thanks. I'm going to start by changing the condenser (I really hope this is the problem because it is an easy fix). I will move on to the other recommendations, to include yours, if the condenser isn't the issue. I will keep you updated.

 

[katy]

When the truck starts losing power, try opening up the gav 1/4 turn, maybe even 1/2 turn.
Have you tried cleaning the carburetor? Checking the jets?

 

[rugreen]

When the truck starts losing power, try opening up the gav 1/4 turn, maybe even 1/2 turn.
Have you tried cleaning the carburetor? Checking the jets?

I actually tried this and openned the GAV a full turn, and even quickly pulled out and released the choke. Both of these provided minimal improvement, so something else is the issue. When I had the high compression head put on recently, the mechanic took apart the carburetor and cleaned it - he said it looked good and didn't need to be rebuilt. However, the carburetor does leak after shutting down the engine, even with the gas flow valve shut. It stops leaking after a short while. So, there is likely an issue with one of the jets, but I'm not sure this is causing the loss of power issue that I described (but certainly something I plan to fix).

 

[Rob Doe]

I recently worked through a problem where a car lost power above 30 mph. It was not heat dependent, but you might check your spark plugs and their gaskets for a leak when the engine gets hot. They should be torqued to 25 foot pounds.

One of the plugs was leaking. It had a light oil streak around it. No backfire on it either.

Unusual spark issues are sometimes created by faulty ground connections, bad cables and wires with broken strands internally or at their ends where connected to ring terminals. Voltage drop testing will identify faults. Voltage drop testing of the Model A electrical system is described in Les Andrew second blue book "Diagnosis and TroubleShooting". Too large of a voltage drop can weaken the spark at the plugs.

I suggest starting at the battery. Charge it. Clean the + cable to the frame to bare metal and tighten, then the clamps at both battery posts. Then the connection at the starter switch. If you have a safety fuse, clean it and its clips. Move up to the terminal box and the coil posts. Make sure all connections are tight.

Good luck. Please report back what is found.

 

[rugreen]

I recently worked through a problem where a car lost power above 30 mph. It was not heat dependent, but you might check your spark plugs and their gaskets for a leak when the engine gets hot. They should be torqued to 25 foot pounds.

One of the plugs was leaking. It had a light oil streak around it. No backfire on it either.

Unusual spark issues are sometimes created by faulty ground connections, bad cables and wires with broken strands internally or at their ends where connected to ring terminals. Voltage drop testing will identify faults. Voltage drop testing of the Model A electrical system is described in Les Andrew second blue book "Diagnosis and TroubleShooting". Too large of a voltage drop can weaken the spark at the plugs.

I suggest starting at the battery. Charge it. Clean the + cable to the frame to bare metal and tighten, then the clamps at both battery posts. Then the connection at the starter switch. If you have a safety fuse, clean it and its clips. Move up to the terminal box and the coil posts. Make sure all connections are tight.

Good luck. Please report back what is found.

Thanks. This is an easy check and I will certainly see if this is the issue.

 

[rugreen]

Update: I have followed a lot of the recommendations in response to my initial post and from friends in the local Model A club:
1. Changed the coil: A friend in the local Model A club mentioned that he had a similar problem and when the engine compartment heated up the coil internal expanded and caused a break in one of the internal coils. This didn't fix my problem, but when I took the old coil off, it started leaking. So, replacing it was a good thing.

2. Set the timing and points gap: Multiple people recommended setting the timing and the points gap. I did these, but they did not fix my loss of power issue. These were easy to do, so a good step in trying to fix my problem.

3. Rebuild the carb: I had a Zenith carb on the truck and pulled it off and replaced it will a Tillotson that I had rebuilt. This fixed my problem to some extent, but not completely. I rebuilt the Zenith and put it back on. However, when I reinstalled the Zenith carb, I also installed a phenolic spacer between the carb and the intake manifold. This spacer reduces the heat transfer from the intake manifold to the carb. These prevented the loss of power issue, but I started having severe overheating issues on hot days.

4. Had my radiator re-cored: To fix the overheating issue, I had my radiator re-cored. This fixed the issue. Although the flow tubes in the old core weren't in terrible shape, there was some blockage the restricted the flow to some extent - even after back-flushing the radiator.

So, the loss of power issue was really an overheating issue. The truck never fully overheated (coolant boiling) because when the engine got hot, it cause the gas in the carb to boil first. This resulted in the engine losing power because it wasn't getting gas. When I switched out the Zenith for a Tillotson, the Tillotson was better at dissipating the heat from the engine and prevented the gas from boiling to some extent (the Tillotson is made from pot metal and the Zenith is cast iron). When I put in the phenolic spacer between the intake manifold and the carb, it prevented the gas in the carb from boiling and allowed the engine to continue to run (no loss of power). However, this allowed the engine to continue to heat up and the coolant would boil - severe overheating. Having the radiator re-cored (and back flushing the cooling channels on the engine) has now fixed the overheating issue. I also removed the license plate from in front of the radiator to the bumper and use a mix of Watterwetter and Sierra antifreeze as coolant. Watterwetter provides a better heat transfer from the engine to the coolant and the antifreeze has a higher boiling temperature than straight water.

 

[Osage Orange]

Great detective work, and understanding what was going on helps all of us when you thoroughly explain each cause and effect.

 

[Rob Doe]

A recent similar problem at our local club was: a single spark plug that was not torqued when installed. 25 foot lbs with a torque wrench and the problem was gone.