fuel delivery issue

[monkeymissile]

Gents,
I am hoping I can get some suggestions; recently I drained all the old fuel from the tank, added about 5 gal of fresh gas, disconnected the fuel line just before the carb and used the priming handle on the fuel pump to get the old gas out of the line. After reconnecting everything and priming the pump again, the truck started right up.
Now, about 3 weeks later, it appears I have mysteriously lost vacuum in the fuel system. The pre-carb fuel filter is dry and so far no amount of priming has worked. I thought perhaps the fuel filter clamps were no tight enough so I went through all those connections and resealed the threads at the fuel line/carb connection, but still no luck. No other connections were disturbed, except I did replace the petcock on the tank. It's not leaking so I doubt that's the problem.
Any ideas? Did my fuel pump fail? It was rebuilt by Then&Now a few years back and was working just fine.
Anything else I should do or check out?
Thanks in advance for any help.

Justin

[ZGjethro]

Is there any way you could run the truck (electric pump from another source?) for a short while and see if the mechanical pump works after a bit? It sounds like you are not getting gas from the tank, or your pump is bad, or you lost vacuum. Sounds like you are on track. Are the bolts holding the pump to the motor snug?

There is no way you turned of the gas by the fuel pump is there?

[w30bob]

Well......if you had two people you could disconnect the fuel line at the tank, put your finger over the line.....and have someone crank the motor. No suction means a bad fuel pump. Other way is to disconnect the fuel line at the pump, put a vacuum pump (hand held Mity Vac or similar) on the line and see if you get fuel. No fuel means a restriction between the pump and the tank somewhere. Those two should narrow it down for you.

regards,
bob

[monkeymissile]

sadly no electric pump or hand-vacuum pump handy and all bolts are tight so I think I'll have to disconnect some fuel lines and test to see where the failure is occurring.

thanks all!

[monkeymissile]

recent developments:
- removed fuel filter (installed between pump+carb) and tried priming handle and was promptly rewarded with a squirt of fuel
- found filter to be clogged and installed another, but no luck; priming handle doesn't send any gas up through
- removed fuel line before pump and tested for suction and got some!
- reattached fuel line at pump, pulled filter off again and tried priming handle, but didn't get any fuel

I am thinking there's an obstruction in the fuel line somewhere before the pump. If so, what is a good way to work it out?

[Tuko]

the priming lever only pumps the last 1/4 of its travel, are you pulling it up far enough? also inspect it to see if it cracked around where it is attached to the pump mine was broken and would spin on the pump shaft.

[monkeymissile]

update #2:
- disconnected fuel line at fuel shut-off valve before pump and plunked the end into a jar of gas
- a few squeezes of the priming handle filled up the bowl of the fuel filter nicely so pump works!
- reconnected fuel line and it started right up
- nice

so I guess the fuel pump just wasn't strong enough to prime by itself and the system had to be wet-primed.
I am still curious as to why it had drained itself. I'd hate to have to do this again!

[Tuko]

do you have the new style needle valve in the carb inlet with the rubber tip?

[monkeymissile]

do you have the new style needle valve in the carb inlet with the rubber tip?

no idea, haven't pulled it apart. I am assuming it's original. What is the advantage?

Thanks

[Tuko]

the rubber tip seats better and wont let the fuel gravity feed towards the fuel tank as much therefore loosing prime. The carb rebuild kit I got came with one. I cant say for sure if it will cure your problem but its my theory why they went with it. like holding your finger on a straw in a cup full of liquid then taking the straw out. drink stays in straw until you take your finger off the tip of the straw. same with needle valve. not seating well fuel may drain back?

[monkeymissile]

the rubber tip seats better and wont let the fuel gravity feed towards the fuel tank as much therefore loosing prime. The carb rebuild kit I got came with one. I cant say for sure if it will cure your problem but its my theory why they went with it. like holding your finger on a straw in a cup full of liquid then taking the straw out. drink stays in straw until you take your finger off the tip of the straw. same with needle valve. not seating well fuel may drain back?

make sense, I'll see how it looks in the morning. Funny how it's been fine for years and is now suddenly having problems. Not sure when my recent activities could have affected it, but it must be related!

thanks

[m37jarhead]

It would make sense to check the entire fuel delivery system. From the in-the-tank filter to the fuel filter on the firewall and all the other in line filters. Maybe the inside of the float bowl two. You might also disconnect the fuel line at the top of the tank and at the shut of valve in the engine compartment. Put some high pressure air to it and
see if it forces out any crud. Might be a clue to crud that has collectd, somehow, in the fuel pump and/or the carb or fuel filters and lines.
As many on this forum have suggested in the past, an aux. electric fuel pump is probably your best insurance against poor fuel delivery problems, vapor lock and
other "mystery" fuel delivery problems. Let us know if you find any other cliches in your system.
JB

[m-37Bruce]

OK, I am having some of the same symptoms, intermittent fuel delivery, yada-yada. So if you install an electric fuel pump, take the mechanical pump out of the equation, is a relay necessary, or should it be part of the harness/switch module? My carb is a Zenith #29 and my pump is a early WC Model. Also, I'm 12 volt, so I am electrically compromised too!

[monkeymissile]

It would make sense to check the entire fuel delivery system. From the in-the-tank filter to the fuel filter on the firewall and all the other in line filters. Maybe the inside of the float bowl two. You might also disconnect the fuel line at the top of the tank and at the shut of valve in the engine compartment. Put some high pressure air to it and
see if it forces out any crud. Might be a clue to crud that has collectd, somehow, in the fuel pump and/or the carb or fuel filters and lines.
As many on this forum have suggested in the past, an aux. electric fuel pump is probably your best insurance against poor fuel delivery problems, vapor lock and
other "mystery" fuel delivery problems. Let us know if you find any other cliches in your system.
JB

well, new fuel lines may have just moved their way up my list of new parts/projects.
Thanks for all of the suggestions and will let you know what I discover.

best,
Justin

[Cal_Gary]

I'd add to make sure your tank is vented-if the cap has the fording switch and is in the incorrect position (closed), vacuum build up in the tank can prevent the fuel from flowing.
Gary