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74 d100, 318

moparkrazed

moparkrazed

Active Member
Joined
Dec 22, 2024
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Location
columbia, sc
Hello again guys. Got my fuel system in but not drawing a lot of fuel to the filter and none to the carb. If i hook up a gas tank under the hood the truck will run all day. Im thinking maybe there is a clog in the line somewhere? I assume u could have a partial blockage in the line. I also removed the gad cap to make sure it wasn't a pressure issue.
 
Have you replaced the old rubber fuel lines? The original lines were not exactly made for today's fuel and can and often suffer from interior hose failure. When that happens, fuel get blocked. You may also want to check the fuel pickup in the tank.
You say new fuel system, but we don't know what was installed.
 
7mopar said:
Have you replaced the old rubber fuel lines? The original lines were not exactly made for today's fuel and can and often suffer from interior hose failure. When that happens, fuel get blocked. You may also want to check the fuel pickup in the tank.
You say new fuel system, but we don't know what was installed.
Click to expand...
I've replaced all the rubber hoses, filter, and just put a new fuel pump on it to see if that did anything. It doesn't have a fuel pump in the tank, it has a mechanical fuel pump. I've narrowed it down to either a blockage or pin hole in the hard line or a issue with in line related to the fuel sending unit. I don't think im going to pursue it further bc im going with a sniper kit and all of this work is going to be pulled out anyways. Ill prob. Pull truck to the exhaust shop. Let them run the new exhaust and then drop the old tank and install the metal one that has a fuel pump already installed.
 
74 should have a poly tank inside the frame rails. I would have dropped it and checked the fuel pickup screen and cleaned the tank. Sniper kit will be a great improvement. Just make sure the in-tank fuel pump matches the system requirements. Also have the exhaust shop install the O2 sensor bug for the sniper unit.
 
7mopar said:
74 should have a poly tank inside the frame rails. I would have dropped it and checked the fuel pickup screen and cleaned the tank. Sniper kit will be a great improvement. Just make sure the in-tank fuel pump matches the system requirements. Also have the exhaust shop install the O2 sensor bug for the sniper unit.
Click to expand...
Yeah. Mine has the plastic tank but its from a 72 longbed. On the sniper kit I ordered the whole thing as a package. I think the fuel pump is 50-55 psi. Im going to get the exhaust shop to weld that bung in as well. I didn't want to use the clamp on thing, it seems like it would suck air eventually.
 
When you replaced the rubber lines;
Did you reuse the factory clamps?
or did you install "gear-clamps"?
Gear-clamps have a nasty way of bunching up the fuel-line, which allows the fuel pump to suck air? If/when I am forced to use them, I use two of them side by side, with the heads offset 180* to prevent that.

Also;
If I can prove that no rubber lines are sucking air, and that the hard lines are clear; then I remember, that the fuel pump eccentrics don't always last 40 plus years.
What I would do next is put a vacuum gauge on the fuelpump inlet, and see how much, if any, vacuum it is capable of drawing.
If the line is plugged between the pump and the carb, the pump may pull a little vacuum. Loosen the line at the carb, and try again. If you now get vacuum, the float-valve may be stuck, or the bowl is already full, in which case the pump can neither push nor pull fuel. But
If zero or near zero, take the pump off, clamp it in a vice, and manually stroke the lever. If you now get vacuum, you'll have to inspect the eccentric thru the pump mounting hole.
Good luck.
 
Last edited:
moparkrazed said:
I've replaced all the rubber hoses, filter, and just put a new fuel pump on it to see if that did anything. It doesn't have a fuel pump in the tank, it has a mechanical fuel pump. I've narrowed it down to either a blockage or pin hole in the hard line or a issue with in line related to the fuel sending unit. I don't think im going to pursue it further bc im going with a sniper kit and all of this work is going to be pulled out anyways. Ill prob. Pull truck to the exhaust shop. Let them run the new exhaust and then drop the old tank and install the metal one that has a fuel pump already installed.
Click to expand...
Just curious, why a metal tank with todays fuels?
 
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