1969 250 i6 soft fuel line size
 

Hi all, I’m going to replace the soft rubber fuel line that runs between the tank hard-lines and the fuel pump on my 1969 250 i6. There is a stretch of soft line that’s maybe 18inches long - really old and brittle on my truck.

Before I order, I just wanted to confirm what was the oem softline size? Can anyone confirm?

Thanks

Luke

Re: 1969 250 i6 soft fuel line size
 

I6 is 5/16" ID. Small block and big block are 3/8" ID. Any auto parts store should have it.
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Re: 1969 250 i6 soft fuel line size
 

Thank you for the confirmation! I thought it was 5/16”

So you’re saying that even i6 and v8 hardliners have different diameter?

Gas tanks are identical however?

I’m asking because at some point I may want to do a v8 swap.

Re: 1969 250 i6 soft fuel line size
 

Inline 6 gas 5/16 diameter hard lines as well as a specific 5/16 flared fitting at the sending unit

All v8’s have 3/8 sending unit to carb

Re: 1969 250 i6 soft fuel line size
 

I believe V8s with a two-barrel carb also had 5/16 line. That's how my '68 was.

Re: 1969 250 i6 soft fuel line size
 

That’s helpful

How much power will a 3/8” line support before it becomes a bottleneck?

Re: 1969 250 i6 soft fuel line size
 

Smart money would be to buy the sender with the 3/8" line if you are replacing it, and use an adapter to reduce the line the rest of the way. No point in buying things twice, and an adapter is cheap. FWIW, I put a 4 barrel carb on my '64 Malibu with a 283 and a powerglide trans. Same 5/16" fuel line got me to 120 MPH. How fast and quick do you want to go?

Re: 1969 250 i6 soft fuel line size
 

That's true. My 69 still has the OE 5/16" line that came with its 307. It was enough to support a 383 revving briefly to >5,500 RPM, and maintaining 2,300-2,500 RPM on freeways.

However, GM must have had a good reason to use 3/8" line on 4bbl engines, because they typically reduce costs wherever they can.