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Vapor Lock in a fuel line...

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How close can a copper fuel line get to an exhaust header without creating a vapor-lock situation. My fuel line is close and I'm having an intermittent fuel starvation problem... that promptly goes away if I pull over and let thing recover (in just a few seconds it seems). 1275cc with two HS2s.

I haven't checked the general fuel flow rate to the filter near the carbs (but the line is new as is the SU electronic fuel pump). I know the carb floats are good... and I think the carbs are fine too. Again, it's an intermittent thing where I start to lose power and the car sputters, but will catch if I ease off. It only happens when it's warmed up (here in cool weather Portland).

I noticed that the previous owner put the fuel line (during re-assembly) rather close to the exhaust header as it comes up from below. So, although I'll re-route it abit, I just wondering what is "too" close. Thanks.
- Mark

P.S. - I decided to toss in a photo that might help.
 
Well, that surely is. I would feel good with 3 inchs. Two inchs if necessary. Should not be difficult to route properly, we all have.
 
The normal routing of the fuel line is in front of the motor mount- that way the line is protected from the heat better. Extend the copper 6 more inches and you will have better success.
BillM
 
Get it as far away as you can and switch to steel. Pure copper is a bad idea as it work hardens ( become brittle with vibration) and can crack. While I've never seen a copper line fail in service, it's common practice not to use pure copper for fuel and brakes.

If you used copper in a fuel system in my school, you would get hit by a flying text book.
 
Billy said:
If you used copper in a fuel system in my school, you would get hit by a flying text book.
Click to expand...

Gotta concur. Copper and aluminium are not good choices for automotive application, IMO. Modern cars now have both in abundance. UGH. Have seen plenty of aluminum A/C lines embrittle and leak. Not as much with copper, but it would never be used as a fuel conduit. Coolant, maybe. In a pinch.

...but I object to putting solid-state devices in 'em as well. Curmudgeon #1 here.
 
Joining the doctor as a curmudgeon, I am.
 
Thank you all. I'd wondered about the copper... especially as it moves about with routine engine roll and vibration, and putting it forward of the engine mount will surely be a good distance from any serious heat. I'll get right on it.
- Mark
 
I have also heard arguments against copper fuel lines. The argument I have heard against it is that it fatigues from engine/chassis vibration.

So... I have a question about this. If the copper is fully supported along its length using P-clips and connected to to the other fuel lines and carbs with rubber hose, is fatigue really an issue? If the tube is not free to move about anywhere is fatigue a problem?

Moving from that, I have seen many brake line kits made of copper alloy tubing. Just like my question above, I assume that since brake lines are typically attached to the body at various points the copper alloy brake tubing does not experience fatigue.

Have I missed something? Is there a different failure mode to watch for?
 
Interesting read, I knew that but had never read a complete paper before. Thanks.
 
Adding this from a good friend (and in another group):

Copper and Cunifer are not the same. "They Say" not to use pure copper lines in automotive applications because they can become brittle. Brittle leads to cracks, leads to leaks, leads to fires, which are considered A Bad Thing. CuNiFer is an alloy of Copper, Nickle and Iron and is what the English use for brake/fuel applications and is generally considered OK to use. If you trust the English.

I have used very short lengths of pure copper piping in the XJ6 at the ‘pickup’ end – so, no FI pressures. No problems at all, and no corrosion, as opposed to the steel pipes I removed. If the copper isn’t subject to vibration it shouldn’t really be an issue, I would think, even with ‘pure’ copper, but on the other hand it takes a VERY long time for decent steel pipe to degrade in our still-relatively-salt-free road conditions…
 
Copper-nickel ALLOY would be fine. Copper is what I'm whining against.

Doug said:
So... I have a question about this. If the copper is fully supported along its length using P-clips and connected to to the other fuel lines and carbs with rubber hose, is fatigue really an issue? If the tube is not free to move about anywhere is fatigue a problem?
Click to expand...

If the copper is well secured, vibration and work-hardening are lesser issues. Vibration at "transition points" like the bulkhead-to-engine <span style="font-style: italic">can</span> be somewhat mollified with a few coils of the tubing where it goes from bracket(chassis) to bracket (engine).

But there's still the issue of copper being SOFT. Subject to nicks and scrapes, errant rocks or inadvertent "reefing".
 
That was an interesting link. Thanks for posting it and for the further comments on tubing in general.
 
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