Technical 1939 Ford pickup stops uphill

The air cleaner being small and restrictive could be the issue. Take it off and see if that doesn't fix the problem.

 

I'm running an auxiliary electric fuel pump back by the gas tank on my '39 p/u with an 8ba. Use it to prime the carb after its been sitting for a while. Wired it to a toggle switch under the dash. Works great.

 

Could you please send me pictures of how is installed your electric fuel pump, engine fittings,etc?
Does it work at the same time with the original pump?

 

Works with the stock mechanical fuel pump. Electric pump is in the fuel line mounted to the frame just in front of the gas tank. You can mount the switch anywhere that works best for you. Make sure the wire to the switch is only hot when the key is on.

 

Was wondering how you're doing on this.
Previously, I said I thought it could be a low float setting. But you said the carb is new and acts the same as with the old one. I guess we can assume it's not the carb. But it's an assumption.
I'm sure it's either a fuel starvation problem under a heavy and sustained load...as on the long grade...or excessive heat is causing vapor lock. Maybe both.
Is that the usual location for the fuel filter on a flathead? It's sitting right between the head and the oil filter. The gas might be getting too hot, sitting there in the filter. I see the (metal?) line to the pump is fairly close to the head too. Maybe a heat barrier (sleeve?) for the metal line? Relocate the filter? Try running it with no filter to start?
I do most of my "testing" without tools that I really should have...such as a fuel pressure tester. And others suggested that you use one. But you can allow the fuel to be pumped into a container as you crank the engine. If you see a strong stream of fuel, you're probably good. Be safe. Disconnect the ignition so the engine doesn't start...just cranks. Don't set the container on the engine and risk fuel being splashed and igniting. Do this when the engine is cold. Remove the fuel line from the carb and filter and attach a longer rubber line that will reach to a container sitting alongside the car...on the floor or a table. Secure the line so it won't come out of the container. A glass or clear plastic container will allow you see the stream.

One other thought.

Years (and years) ago, I bought a 10-ish year old '70 AMC Javelin SST 390 auto. She'd scoot. But it would run out of gas on a hard run. Just die instantly. The previous owner had mounted the Holley electric fuel pump under the hood. Turns out electric pumps are better at pushing than pulling. I didn't know any better until someone told me. Relocated it back by the tank and all was good.
Now, I don't know a lot about the flatheads. And I'm not sure how this relates to your problem. I mean, almost every other flathead has the pump on the engine. But I wonder if it's something before the pump...even though you said the tank is clean and the lines are new. I've had debris clog the fitting under the tank. If there's a screen, it doesn't take much. And I think that even the smallest leak in the line before the pump could introduce air and cause the pump to not draw fuel as well.
Just check for good flow at the inlet at the carb. If it's good, it has to be dirt in the carb, a low float setting or vapor lock. If it's weak, you have an obstruction, leak, or bad pump. If you can't find obstructions or leaks, I'd pull the pump apart and see if the rubber diaphragm has a small rip or hole in it.

 

Back in the day when stock Flathead Fords were common as daily drivers some with high mileage were known to have the cam lobe that activates the fuel pump pushrod wear to the point of causing fuel starvation issues. Shim jobs by various means offered a quick but usually temporary fix. Short of an expensive teardown to replace the cam, installing an electric fuel pump offered the most reliable fix. Be aware that an oil pressure issue might arise if the pump pushrod is removed. IIRC there is a bushing oil hole that should be plugged if the pushrod is removed.

Ed

 

^^^^^^^^THIS happened with my ‘46 Ford back in the day! Congratulations Ed, I was going to post about the cam lobe wear possibility......couldn’t believe no one mentioned that given all the posts, but you did! May not be the problem, but definitely needs to be checked.

 

My good buddy had a stock '40 Chrysler that would stop going up grades.
He traced to a crack (leak) in a rubber hose. When the car was on the grade (front higher than the back) the stock fuel pump would suck air and not the fuel from the tank.
Replaced the hose, and no problems.

 

Guys you are very helpful, thank you very much for your suggestions!
Right now the pickup is having a minor body work, as soons as it is finished, I will test all your suggestions. Also I noticed that there are three fuel filters, perhaps that creates the issue as well.
I am going to leave installed only one.