I have a 96 Bronco.....But... I have a question about my farm truck, 79 chevy 3/4 ton camper special...dont hate. I trust the help and advise I have gotten here and yes I would rather find, and am still looking for a 70's ford w/460 for the camper-extended cab. Until then I have a fuel flow problem.
Sending ubit had three stems= fuel feed, vent and a line for charcoal can. I eliminated the charcoal can. If truck sits for a few days I have to prime the carb with gas to get it to start. After that it runs great. the fuel filter "see thru" does not fill with fuel EVER, but it does run strong- will smoke all 4 tires... What is wrong in my fuel system
*replaced and tested mech fuel pump
* new lines- cant find a kink
**have heard a whistling sound from one of the gas caps indicating a problem but now it is gone.
Will answer any other queries to try to get to answer and thanks in advance for any help.

I hope we are all adults and everyone will respect that I trust this site for your advice and I am sorry it is for an evil chevy... but my heart is true BLUE OVAL...

 

a mechanical pump may be partially working and still not provide enough fuel. its also possible the float in your carb isnt set properly. its probably time to rebuild that carb or put somethign else on there.

did it do this before the charcoal can was removed? if not then put it back haha.

might see about ventalating the tanks,

 

I did rebuild carb... NO garuntees I did it correctly because it does run, and runs well, BUT i was concerned about the floats because I neither new how to check or adjust them. The pump is NEW, I know it is no garuntee.
But, just so I am clear i really should see a large volume of fuel build in that little clear gas filter and see it drop a hai as I mail it and then build back up when the mech pump catches it. Right??

 

if your carb bowl is dry then something isnt right. there should always be fuel in the bowl where the float is so try adjusting that up a bit.

 

Rebuild or just replace the carb, the fuel is leaking out as it sits.

So it has to pump up to fill the carb bowl before it sends fuel thru the venturies.

 

I don't think he ment the bowls. From what i see, what's happening is after the truck sits for so long all the fuel in the lines drains out so he has to prime the carb manually to get it to run and suck more gas down. I'm not sure why there would be no gas in the filter container, it should be completely full when running and still have a lot in there when not. Only thing i can recommend is searching along the line for any leaks that could be allowing the fuel to evap before it drips.

 

I don't know much about this subject or if your truck would have this or not but..

My brothers truck, a 99 Isuzu hombre (a chevy s-10 with different headlights), has problems starting when it sits for a while. It takes a long time cranking and doesn't seem like it will start but eventually it does after a few times. However, when it starts, it runs perfectly and doesn't have any problems starting within a short amount of time after driving. He had his fuel pump and filter replaced and still has the same problem. The diagnosis is that there is a check valve in his fuel lines that has gone bad and lets the fuel slowly drain out so he loses pressure. So when he tries to start, the fuel pump has to pump gas all the way from the tank to get it to start.

Are all the fuel lines new? And if not, do you know if any of your fuel lines have a check valve? Because if so, that may be worth looking at. Or if not, like Gruesome said I would definitely check for leaks along the fuel lines.

Like I said, I don't know too much about this subject and haven't had the opportunity to mess around with a carbureted engine yet, but the problem sound similar to my brothers problem so it may be worth a look.

 

I don't think a carbureted vehicle has a check valve does it? Then again i don't have the slightest clue..

 

Yeah that's what I was wondering. I don't know if they do, but then again if it does maybe it's worth a look. Otherwise like you said, at least checking for leaks may be a small start.

 

Most I have seen the mechanical fuel pump IS the check valve. If there is any loose fittings anywhere that will let air in it can drain off or back to the tank. My guess is the fittings on the new pump are sucking air and letting the pressure off when it sets. Maybe use some thread tape there. Than there is the issue of no gas in the carb. Most likely a leak there also. As the engine is hot when shut down and the gas is leaking out slow it may be evaporating and thus no puddle on the manifold. Try filling the carb with a small squeeze bottle in the vent tube on top of the carb when the engine is cold. Look for a leak. I have seen the fuel drain back out of the carb also do to it sucking air from a bad fitting somewhere in the fuel system. Not all carbs can do this. And a leak that will suck air and drain the system back to the tank may not leak gas. Or leak much more than to just be wet but not drip.

 

Most issues I have seen with carbs being dry after a time ended up being a bad/warped part in the carb. For it to be a line/pump/filter issue the fuel most be sucked up inside the carb to be able to run back down the line. Internal parts like jets/metering rods/check ***** can cause this.

I have owned several classic vehicles and have seen this a few times, Ended up replacing the carb most of the time.

 

OK... THanks to ALL so far.

All rubber lines are new, steel lines not, but no check valve there that I see.
I have been wondering if the sending units cold be a weak link in this but if it runs well when running I have eliminated them for now.
ALL logical solutions point to a crappy mechanic on the carb rebuild (ME)!!! I will investigate the options to this point and keep everyone up to speed.
** Hey it was my first full rebuild (done for stress relief) I removed each and every bolt from EVERY OTHER BOLT... at one time a frame on jack stands..... and the damn thing will spin ALL 4 tires...
I will add pics for this and the BRONCO beast. Last quote is from the wife about backing the Bronco INTO the Chevy 1 week after painting both (yeahhh gotta luv her)

...These damn things are tough because I hit hard enough to jar my neck and back and there is ,like, nothing wrong with either... I replied thats right hunnie we may be old, but we are still tougher than anything born in the 21st century...lol (there is about 19 years difference between the wife and I....) and yes she is WELL over 21... closer to 30

 

Haha nice, these really are some tough trucks. IT is understandable that there may be a leak in the carb itself, you can't get it perfect everytime.

 

first off, ( for me ) it doesn't matter what emblem is on the grill- they all have their share of faults and goodness. Float height is easy for a Q-jet, you hold the upper body upside down level to the ground and adjust the float until it looks level. You adjust it by bending ( CAREFULLY) on the tab that pushes in the float valves.

Look at the fuel filter while the engine is running, the clear body should fill up with fuel, if it doesn't, there's either a very weak fuel pressure or there's a cut/rust hole or kink in the fuel line some where allowing air to get sucked in, the fuel pump is weak ( as mentioned before), or you bent the metering rods when you re-assembled the carb, allowing the fuel to just dump into the main venturies.

 

If the truck is exposed to the elements for long periods of time, I would check the hard lines for rust spots, and the rubber lines for area that look like the hose is turning into goo. Whens the last time the tank was cleaned? Debris in the tank maybe? What carb are you running?