starves for fuel when warmed up

[Seatown-gmc]

I have a 2wd 1970 GMC pick up with a factory 396. The truck starts up everytime and idles fine but when it warms up and im driving the truck it sputters and pops like it is running out of gas. I thought it was the fuel pump so I changed it. Not the problem. so I put a clear filter on the fuel line so i could watch the fuel and see what it was doing. when the motor is cold the filter is full but when the motor heats up the filter gets bone dry the motor must be runnng on fumes only but it doesnt die. The fuel intermitently skirts into the filter after it is warm but not what it should be. My truck does have headers do you think this is my problem?

[So.Cal.Super]

first, Welcome to the board.

Second, I have headers and the problem I am fixing is the sock in the tank. Check out my post here and you can see pics of an almost 40 year old tank sock.

http://67-72chevytrucks.com/vboard/s...d.php?t=434265

third. There is no other filter between the tank and pump correct?
(discussing this on my post also)

let us know.

[Jacfourteen]

Originally Posted by So.Cal.Super

first, Welcome to the board.

Second, I have headers and the problem I am fixing is the sock in the tank. Check out my post here and you can see pics of an almost 40 year old tank sock.

http://67-72chevytrucks.com/vboard/s...d.php?t=434265

third. There is no other filter between the tank and pump correct?
(discussing this on my post also)

let us know.

Same thoughts I had, also how is the condition of your tank and lines? If they are all cruddy they can clog up.

[Seatown-gmc]

there is not a filter between the pump and tank other than than the sock in the tank. Im sure that the sock in the tank is factory and has never been changed. Do you think that would affected the way the fuel flows when the motor is warmed up though?

[So.Cal.Super]

When I started mine cold it was at 7.0 psi, just what the regulator was set at. Over the course of idling for 30 mins it was dropping .5 - 1 psi every 5 mins or so. When I would hit the throttle, the pressure would drop to 0. When I shut the truck off the line would fill back up and I would have more pressure on the next start up for a few mins.
I have full length headers on a big block and the fuel lines are 99% in the stock locations minus what I modified above the valve cover for the Regulator, heat was never a problem.
In the last few months the truck would run half throttle but fall on its face above that. From a dead stop it would run through first and second then nose dive like I hit a pole because it had sucked the fuel line dry. If any of these problems sound familiar there is a chance it’s the sock or from what I have read pin holes in the pickup tube due to rust and age.
Hope that helps.

[Seatown-gmc]

do I have to take the tank out to get the sending unit out or just remove the seat? also I have two other tanks on the truck I have ran it on all three tanks and it does the same thing do you think it is likely that all three socks are clogged or have you guys ever heard of the tank selector valves causing a problem?

[lindstromjd]

It could be a vapor-lock, too. Since it only does it after it warms up, that would suggest that heat is a factor. How close does your fuel line run to your exhaust?

[etg]

You don't have to remove the tank, and you don't have to remove the seat but it helps. Have a flathead hand, and poke a tab until you turn the locking wheel/plate enough to loosen and pull it off. You'll have to undo the fuel line, make sure you have a rag and no open flames . Also be careful you don't puncture the float.

[cdowns]

it could b wrong gascap, after running try taking cap off if there is a wooshing noise that means you have later style cap and your tank isnt venting

also if you have the stock carb . there is a fuel filter inside the carb, where the inlet tube goes in carb that very big nut on the carb body holds filter in place

[RenoKeene]

^What cdowns said.

[So.Cal.Super]

Originally Posted by cdowns

it could b wrong gascap, after running try taking cap off if there is a wooshing noise that means you have later style cap and your tank isnt venting

also if you have the stock carb . there is a fuel filter inside the carb, where the inlet tube goes in carb that very big nut on the carb body holds filter in place

Never thought of the gas cap, what makes me think it's not the carb filter is he mentioned The sight glass on the filter he has emptying and that it's between the pump and carb. now i'm curious...

[Seatown-gmc]

I looked at how close the header gets to the fuel line last night. It's pretty close I would say less than a half inch or so. The fuel line is in the stock location running in the center of the frame rail. I think it might be getting cooked!
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[Seatown-gmc]

Also the wrap on the headers looks pretty old and looks like Hellen Keller put it on. There is slot of spaces between the wrap.
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