Kazoocruiser

The truck is a 1981 C10 with a 250 inline six. It has a two-line mechanical fuel pump. I want to convert it to a three line, since I am going to have to replace the sender in the fuel tank, because I think if has a cracked pick-up line in it. Once I know what parts I need, I can run the additional return line from the pump. I think this will help me with what I think was fuel percolation issues this summer. For all I know, it might have been the pick-up unit failing anyway. Before I run the third line, I can cap off the return line to the tank

Thanks in advance for the help!

oilcanhenry

If you have a carburerator, whats the third line going to be for?

I am not as familiar with the integrated-head inline 250 six, as I am with the older GM 250 cubic inch mill.

Kazoocruiser

Hi oilcanhenry, the reason I am considering the option of adding a third line is to allow fuel to circulate back to the tank from the pump, in an attempt to keep it from boiling in the lines and causing percolation. I've run into this a couple of times when I have been stuck in traffic on 90+ days. The engine will shut off for lack of fuel, and then I have to open the hood up and pour cold water on the pump to get it to start pumping again. I've replaced the pump twice. I thought the original pump had just worn out, but the second, brand-new pump did it too.

oldchevy

Won't a return line reduce flow to the carb and therefore cause another problem? Check your fuel line from the carb to the pump and make sure it is not against anything that gets hot such as a manifold or radiator hose, etc. In the old days we used to correct this problem by putting 2 wooden clothes pins on the fuel line one close to the pump and one closer to the carb.

Kazoocruiser

Hi oldchevy, thanks for the question. I found this information in the manual I was able to locate:
ST_330_81_1981_Chevrolet_Light_Duty_Truck_10_to_30 _Service_Manual.pdf

and according to what it indicates, psi on the existing unit is 41/2-6.
A V8 with a vapor return line is supposed to show a pressure rating of 51/2-7

So it looks like even under a lowest number scenario, the three-line unit puts out more pressure.

I guess the question I have is what would be a part number for a 3-line pump for an inline 6.

Until I drop the tank and inspect the pick up unit to make sure it is bad, all of this is just potentially useful.

oilcanhenry

Well ethanol-gasoline doesnt help with percolation at all, but even regular gas can perculate .Does your Chevy 250 I-6 have the 2-BBL Rochester Varajet Caburetor or something else? I'd look into a heat shielding spacer. The best ones were made of Bakelite, which was used before plastic was commonplace. Aluminum ones would work
too. Also I'd think about wrapping the fuel-line with self-sealing aluminum heat shieding used by HVAC installers and roofers. Its not very expensive and easy to apply.

Kazoocruiser

Hi oilcanhenry The truck is stock with the Varajet 2bbl. Today I went out and pressurized the tank with the vent line pinched off, and I had all kinds of gas leaking at the top of the pickup line where it goes through the sender and into the tank, so I went ahead and ordered in a two-line stock replacement. Apparently the pickup had a stress crack in it that didn't show up until the new tank was installed. Note to self: Replace sender at time of tank replacement to avoid a 4 hour do-over. Maybe my problems will go away with a new sender.

One can hope.

Kazoocruiser

I did some more cogitating on this. Another reason a third line would be helpful is that the line could be broken and used to supply an external container.

If things come unraveled like a golf ball does when you strip off the cover, gasoline is going to become really volatile. I like the idea of having 20 gallons, or having the ability to carry that. I might add a second tank with all of the plumbing that would be necessary. But that, and a motorcycle, might allow me to cushion the shock of what could be 6.66, 12.00 or more dollars per gallon of the stuff apocalyptic nightmares are made of. The third line allows the engine to continue to run while the pump sends fuel back to the tank.

oilcanhenry

Yeah, we are living in very interesting times, that's for sure. Looks like the three- outlet 350 pump will work on your 250 to me, judging by the pictures I have seen. Should have enough fuel pressure to allow for the 4.5 PSI lower limit or more, at a guess. Yeah, I hate working on gas tanks, even if its a pickup, without a lift or a hoist around anymore, but I did a few years back. It was a nightmare with all the fuel vapor cannister and assorted hoses and wires down there. As for an extra fuel tank, and old propane tank would work, if mounted in the bed. They come in 90-120 gallons for the portable ones, and they are thick as hell too!
Used to see lots of people using dual fuel motors that allowed for a carburetor motor to run either, but propane doesn't have as much power as gasoline does,

Kazoocruiser

Here is a link to my build thread. The latest posts are on the 4th page.

@https://www.streetsource.com/threads/142462/mazda-projects-pretend-its-long-bed-mazda