87Brougham

Hey y'all, background info:
1972 Olds 350 being put into a 1987 El Camino. The El Camino has three fuel lines, and an in tank pump. On the new engine, I have installed a 2 line mechanical fuel pump.
My question:
What are the three line vs two line uses? Without having to buy and install a different pump, what modifications may I have to do to use the two line pump in the 3 line car? How would I remove the in tank pump and set up the tank for a mechanical two line system?

Inline

3 lines - the 3rd line is for exhaust fumes- it pulls them from tank to "charcoal canister" from where the fumes get pulled to engine to be burned. Atleast in Cutlass the vent-line is on drivers-side frame. Nothing to do with fuel-pump.

joe_padavano

No, no, no. This topic must get discussed here about once a month.
Olds used fuel return on cars with high underhood temps to recirculate hot underhood fuel back to the tank to cool. This was done to avoid percolation and vapor lock. There is one suction line into the fuel pump. On fuel return cars, there are two pressure lines out of the pump - one to the carb and a smaller one back to the tank. That smaller outlet on the pump has a restrictor orifice built into it to maintain pressure to the carb. I assume your in-tank pump on the Elco is because that car had TBI, right? If so, your lines from the tank are pressure from the pump and return back to the tank from the TBI pressure regulator. The vapor line to the charcoal cannister is a separate line. You can use a two-line fuel pump, just cap the return line back to the tank, but you'll be better off with a fuel return pump on the engine. Have you removed the electric pump from the tank or are you planning on trying to suck through it? That might be an issue.

87Brougham

Thank you Joe, that was very helpful. Yes, the Elco had TBI. I was planning on removing the electric pump, but it doesn't sound like it would be as simple as just removal.

My build is quickly progressing due to being home for spring break, and I am just now getting into the build again for the first time in 3 months. It seems as though the more time I take off from working on it, the less I understand. Unfortunately, this build has now taken just so long and now I am having to rush a bunch at once, without really understanding what or why I am doing it. It doesn't help that I move in May, so I am in a rush to get everything put back on my car. Sorry for the little rant :/ Thanks again Joe.

joe_padavano

I would just get the tank sending unit from a non-TBI ElCo and avoid any issue with trying to cobble something around the pump.

olds 307 and 403

We have done the conversion on a Caprice. The owner had no issues running a carb through the TBI pump with a mechanical fuel pump on the motor and the in tank pump just sitting in place with the relay removed.

joe_padavano

Good to know, thanks. I have no experience there. Given that the TBI pump is only 15 psi, it's even possible to use it as a priming pump for cars that sit for a while. There is also a fuel pressure regulator available that knocks the 15 psi down to 5-ish psi for carb conversions to TBI cars.