Burning Fuel

[Yoshi]

1980 K10, 350. So I fill both tanks and use the left tank first. After only 50 miles or so, the engine quits as if the left tank is out of gas so I switch tanks. Right tank gauge reads full but gets to "e" in about 40 miles. So I switch h back to left tank and it drives another few miles until engine quits as if running out of gas. So I drive on the right tank for a couple miles (on "e") then the engine quits as if it is running out of gas. So I switch back to the right tank a drive, and this cycle repeats.
Any ideas on what is happening?

[VileZambonie]

Loosen the gas caps and see if it still happens

[Yoshi]

Ok. The first time it happened I noticed that gas was coming out of the right tank so I replace the gas cap. The old gas cap was at least 20 years old. I have not replaced the left gas cap but I'm going to do that now and then drive it. I will let you know how it goes.

[bd]

Vile said, "loosen the gas caps..."

Loosening the gas caps will help determine if there is a fuel tank venting problem.  If the tanks are not properly vented, fuel will not draw correctly, resulting in the symptoms that you experienced.

So, loosen the gas caps and drive it for 50 miles, or a suitable amount of time/distance, to see if the symptoms go away.  Stay sharp and watch for any fuel spillage around the caps.


Now, if fuel begins to ooze out from under the right fuel cap while you have the left fuel tank selected, or vice versa, there is a fuel selector valve plumbing issue.

[Mike81K10]

If you find you don't have a venting problem! Have you checked your fuel system for debris in the system. If your fuel lines have something in them they could run a bit until it clogs your line, then when you switch tanks the fuel can subside and then run awhile until it get clogged up again. I would take a look at your filters, in your tanks, and your selector valve to see if any debris is visable. Ethanal in fuel today can cause rust and sludge in the 73-87 square body trucks. It messed mine up real bad.

[bedwards]

Sounds like your tank switch is not fully switching, leaving the return line on one side while running on the other, this can be very dangerous if you continue to drive like this. When the other tank gets too full it will go into the vent line and then into your carbon canister, ruining it and finally into your carburetor through the  vent line. Ask me how I know  =[

[Yoshi]

So I drove it again. The last time I drove it I was using the left tank because the right tank registered near empty. After starting, I switched to right tank out of curiosity and it read at half. After driving 9 miles, it was reading a quarter tank, so I switched it back to the left. Today I checked the left tank, after driving about 7 miles, and it reads half again. I'm ordering a new sending unit for my left tank, so while i'm at it I'll check both tanks for debris. I'm also going to order a selector valve, then install it. It's gonna be a few days but I'll let y'all know what happens.
Gotta wait for payday. 😁
Thanks a million for the help. 👍

[Mike81K10]

You can see some of the pics in my build thread how bad my sending units and fuel system looked. The inside of my tanks were really bad and my whole system was in bad shape from rust and sludge.