Halftrack Stalling/Fuel Problem Help

[Lordsandy]

So, I've had a problem with my M16A1 Halftrack Stalling on occasion and I'm thinking about running it in a parade 4th of July so I tried to simulate the run to see how it would go.   I ran it today for just over two hours with no problems and temp was at 180 on the gauge. I had it in 1st and 2nd gear, go for a quick ride, let it idle for a while and go again with no problems then one time I had it in 3rd gear and slowed down in she stalled like it needs gas. Started right up and stalled again. This is what typically happens.
I open the hood and remove the brass plug on the side of the carb and don't see any fuel. I tap on the filter and carb and she starts and I continue to tap and I see the fuel come to the bottom of the threads like its suppose to be and she runs good until I get her home and park it.
I have a new tank, all new lines, new filters, rebuilt pumps (I bought a second because I thought maybe the pump went bad) and a rebuilt carb!
I also check the small filter and clean it but its never bad. Sometimes I remove it and the bowl is  3/4 full of full and other times its full and under pressure that it squirts out from the top when I remove it. What do you guys find when you remove your fuel bowl, pressure or no pressure???
I'm thinking either the main jet gets hung up (I tend to doubt that) or maybe air is entering the system and it gets air locked? I've run with two different pumps and have the same outcome so I don't think it's the pump.
Any thoughts or similar problems in anyone's past???
Thanks in advance for any suggestions or help.
Jim S

[Outsider]

1) Check you gas cap vent as it may not be working properly. When you run in high gear it may be drawing more fuel than the cap will let air in. I would try running it in a higher gear with the gas cap loose and see if that helps.

2) Otherwise I would suspect any rubber hose on the suction side of the fuel pump as they could be internally collapsing when stressed with higher vacuums. Which would pinch off the flow of fuel under high demand applications. (almost all the time with a Halftrack)  

Steve

[Jason Barnett]

Unless you have a hole in your line, or a bad gas cap as mentioned above, it sounds like Vapor Lock to me. Gas in the 1940's was much less volatile and less sensitive to heat. Modern gas is very lite and has a tendency to boil at much lower temperatures if exposed to engine heat, exhaust heat, or radiator heat, and the engine will just quit as if you ran out of fuel in the tank. I would would insulate the fuel lines any where under the hood and certainly anywhere near the exhaust pipe. I have had several of the antique fire trucks and several Model T Fords do this to me over the past few years. Now that ethanol is being added to fuel, the vapor locking problem is worse than ever. I use the burlap like exhaust wrap that most any auto parts sells.

[HenryVIII]

Sounds to me like the needle valve in the carb is sticking. Check to see that the float is not binding or hanging up. If it sticks open you will get too much fuel and if it sticks shut you will get no fuel, but when tou tap the carb you will knock the float down and you will get fuel again.  I have had similar problems with old carbs before. Just my 2 cents.  Henry