Technical FLATHEAD EXPERTS PLEASE HELP.

Ok here goes.
I recently bought a 40 Ford standard. It has original flathead V8 all stock drivetrain. My problem is when it warms up approximately 5 miles or so it starts to lose power it feels like it's going lean and will continue to lose power till I can barely move. So far I have done all the tune up stuff just for basic maintenance plugs points condenser. I also changed to a 6 volt non resistor required coil. I disassembled the fuel pump perfectly clean nothing in there. Disassemble the carburetor was nearly spotless float level seems okay. And has a new gas tank and new lines. It will idle fine the whole time. But you can hold it wide open and it barely revs just sounds like it's sucking air. I pulled the top off the carburetor when it is like this and the bowl is full of gas. Power valve is not leaking. Any suggestions would be great. I'm at a loss. A little background I've been a mechanic for probably 30 years I just never had anything this old. I'm going to have to assume the previous owner had the same problem of course he neglected to tell me and it ran fine on the short test drive. Because he drilled a hole in the gas cap.

 

In addition it doesn't smoke and it runs really good when it runs. Very quiet except for a slight valve taps.

 

Maybe a restriction in the exhaust system.

 

Funny you should say that. I actually own a Meineke. But I don't know how it would take 5 miles for that to kick in. Also I'll probably take it to work and cut the pipe off right in front of the muffler tomorrow just to check because I don't know what else to do.

 

Change the condenser again. Lots of new ones are bad right off the shelf.

 

Check your coil is marked '6 volt'. Some parts shops sell a 12v ballast coil as a sub for a straight six volt. Have seen similar symptoms. Starts good cold, but hard to start hot.. Sometimes a high speed misfire like a faulty condenser.
Let it all cool down and it runs OK again.
Had some good arguments over this one!
Garpo

 

I know you mentioned some valve noise, but some may not have enough lash so the valves will not seat when they become longer with heat.

 

It is. as was the last one.

 

I did with the one GMC Bubba recommended. no change.

 

I doubt this because it runs great when it runs and even has the slight tap when warm.

 

No updates yet but the carb base has a lot of condensation even at idle. No idea if that's normal or not.