So im swapping from a 305 tbi to a 355 with demon 750 carb into my 1989 formula firebird. Im going with a on the block fuel pump. since it came with a tbi there are 2 gas lines coming from the tank up to the engine bay. One i know is a return line. But which line is which? which one is the return line? and do i need to block that one off since im going with a on the block fuel pump and just use the inlet? how do i go about this? thanks.

 

On my mechanical engine-based fuel pump, 1. the smaller connector is the return line; 2. the larger is the actual fuel line from tank to pump and 3. the inlet is for pump-to-carburetor.

 

I hope you're planning on dropping the tank and removing the in-tank electric pump.

 

Yes i am. to get rid of the electric one. but which one in the engine bay is the return line. there both the same size? and i don't need the return line as i am puting a mechanical pump on? Correct?

 

If you check on the driver side under the hood were the the three steel lines come from the tank, ull have one that goes to the canister on the front then two that go to the TBI, the thicker one is the feed line the thinner tube is the return. Hope that clears up your doubt

 

yes that clears it up. thanks you. And i can completely get rid of the return line correct?

 

Dont know , its your car do w/e u like with the line , i guess u can remove it or just leave it there and put a cap on it , its not bothering anything.

 

Using a return line helps reduce or eliminate vapor lock. But, so does using an in-tank electric pump.