Fuel filter empties as engine runs

[Loa]

Hello,

My 1972 340 runs pretty well when I start it, with the (clear) fuel filter half-full. But as I let it run (a few minutes) I see the fuel filter gradually emptying and eventually the engine stops for lack of fuel.

When I bought the car (2 months ago) it worked well, but it started doing that after an rebuild (so the mechanical fuel pump and fuel filter were removed).

Any thoughts?

Thanks

[Oldschool]

Sounds like a weak/bad fuel pump, or a restriction of some sort in the line prior to the filter....

[dfrazz]

   You can blow out your fuel lines, check sending unit to make sure the sock is not blocking the pickup, then go to your pump including the fuel pump rod which is commonly not check or changed out.

[Loa]

Thanks for the tips. I remember that when I put the fuel pump back in, it didn't feel like it was perfect. I tried every possible angle, but the rod didn't want to slip in easily. Is it possible that its cam was in a bad position?

Thanks

[dfrazz]

Usually its either in or not, but it is a PITA to make sure the lever is on top.  One trick i use is get a used up hack saw blade, bend it to a 90 degree angle and slip it in first to hold the lever up then the fuel pump.  The blade is thin enough to allow the pump to slide in then you just pull the blade out and your good to go!

[Oldschool]

I always make sure the cam lobe that actuates the fuel pump rod is at a low point. Then I load up the fuel pump rod with heavy grease to hold it in place against the camshaft while I install the pump. So far I have never had an issue doing it that way.   

[solarguy]

It's a 340, no push rod for pump.  Fuel pump lever rides against cam eccentric

[solarguy]

Floats in carb bowl can also be set too low.  disconnect fuel line before filter, ground coil to disable ignition and have someone crank the engine over a few times while you hold fuel line in a can, see how much comes out.  Could also have a clogged vent line at the tank, try running engine with fuel cap removed.  Could also be a very small pinhole in fuel line that draws air under vacuum.  Just a few  to try

[Loa]

Hello,

Small update: when I removed the fuel filter, the intake nipple was bent and broken. I went and bought a new one, and the engine runs better. But after driving it a few minutes around town, it sometimes wants to stop and I have to give it more gas otherwise it will stall. But if giving it gas solves the problem, I'm pretty sure there's enough fuel in the bowl.

Could it be that the carb is simply not properly tuned yet? (It's a thermoquad, I set both screws to 4 turns open and simply adjusted the idle screw.)

I'll try running without the fuel tank cap.

Thanks

[brasil]

sounds like a vacuum leak...

4 turns out is a lot....  is it a SMOG Carb ?

Greetings Juergen

[Loa]

Hello,

Could be a vacuum leak. The hoses are pretty old.

The carb is a 6138 thermoquad, don't know if that helps with the smog or not. But right now, I've screwed them in quite a bit. No significant change. Sadly, I have no idea how to properly tune it. Haven't checked the timing either, but I haven't touched the distributor during the rebuild process (the block stayed in the car).

[solarguy]

 I haven't touched the distributor during the rebuild process (the block stayed in the car).

what exactly did you rebuild?

[brasil]

6138


is a GOOD ONE !   No Smogger....  base gasket ...  PCV Valve   Brake booster  VC   and the hoses...
Intake gasket .

These are the suspects....  in my opinion

Greetings Juergen

[Loa]

what exactly did you rebuild?

Everything else.

6138 is a GOOD ONE !

Good to know! Any tips on adjusting it to see if it's only that or if I should check everything? I rebuilt it using a kit, so everything I could change has been changed.

Loa

[brasil]

adjusting a TQ is a little tricky...  there are a lot of parameters that "play " together... 

I think that the "problem " you have  is not directly carb related .  Look for the gaskets....

The only thing why a TQ is running LEAN is the wrong choice of JET /rods     or perhaps a blocked Idle ciruit

Greetings Juergen