Vapour Lock Issue

[EXcappa]

I think we're beginning to see the story.

1;The issue only occurs when I sit at 60mph on the highway, it just coughs and dies.
I though the bypass reg and return line had fixed it but not so....although it has helped compared to the deadhead reg.
6;It will not start straight up again, needs to crank for a fair while before it will start.
Also I have a 1" plastic style spacer. (sorry forgot to mention both those points).It takes a good 30mins of driving before it will play up so I assume it is the heat being the problem.
12;The fuel tank was removed and flushed and new filter installed so that cannot be it.
13;I have tried driving with the cap off and it made no difference
15;Everything like lines, hoses, holley etc are all brand new.
16;When it starts to splutter I nail the accelerator to open the mechanical secondaries and it takes off again till the fuel runs out in the secondaries then it just dies. I pull to the side of the road and crank it over for about 20 seconds and then it will fire up again.Prior to installing the bypass reg it was real bad to the point where it would only drive for 2 miles and then stall, get it going again and have the same issue mile after mile.
18;Maybe an electric pump will help.
22;The carb is super responsive.Also runs fine around town when warm.....it just has issues when warm and highway driving.

I believe your problem is between the pump and the regulator.Unless it's sucking air right before the pump

Possibly.

The line between the pump and regulator is insulated to help keep the heat out.
I would also think the bypass regulator would keep the fuel flowing in this area so the chance of heating the fuel would be a lot less.

Sucking air before the pump is plausible but why does it only happen when it heats up?
I have had the pump opened and it all looks great

All fuel lines were installed well away from the exhaust.

 

[Bad Sport]

It will not start straight up again, needs to crank for a fair while before it will start.

It takes a good 30mins of driving before it will play up so I assume it is the heat being the problem.

Well, you say 30 minutes. Is that the norm?

Let's look at it in terms of miles. Might you go 20 miles and it quits, next time might you go 40 miles and it quits.

When you go to start it, does it vary in regards to the amount of time. Maybe one time it will fire up in say 5 minutes, while the next time it might take 15 to 20?

 

[EXcappa]

Well, you say 30 minutes. Is that the norm?

Let's look at it in terms of miles. Might you go 20 miles and it quits, next time might you go 40 miles and it quits.

When you go to start it, does it vary in regards to the amount of time. Maybe one time it will fire up in say 5 minutes, while the next time it might take 15 to 20?

Generally about 20 miles of driving will see it splutter and stall.

It will start up again when I turn the key but it will have to crank for about 15-20 seconds, which I assume is due to the fuel bowls being emptied.

 

[krazykuda]

t distributor are you using? Stock electronic or aftermarket???

 

[AJ/FormS]

Since you're running a mechanical pump, This is what I'd do; I'd run the fuel line direct to the carb, and retest.
Here's my thinking; At 60 mph, your fuel requirement is really low.I think the regulator is unable to properly regulate at that low a setting, and eventually the bowl runs dry.
Either that or the pump is sucking air. Could be anywhere on the suction side, all the way to the sender.
And here's the thinking on that; the usual culprit is the rubber line connecting the sender to the main line, at the back. It's high enough to not leak liquid. And as long as the fuel requirement is high, the pump gets enough fuel. On a bypass system some or most of the air will get returned. That's why I recommended a test for that.
But at low fuel requirements, the pump draws mostly air, and sooner or la.....
Now, the line may be new, as stated, but if the line to sender is not secure, this is how the trouble starts. If using a metallic main line, I double gear-clamp those,180* apart. If using AN fittings, you're on your own, cuz I don't use that stuff.I also don't put filters on the suction side, without double clamping.
When single clamping, the rubber hose tends to bunch up right at the screw. I've had them leak there. Double clamping, 180*apart, eliminates that possibility.

 

[EXcappa]

t distributor are you using? Stock electronic or aftermarket???

Its an MSD distributor

 

[EXcappa]

Since you're running a mechanical pump, This is what I'd do; I'd run the fuel line direct to the carb, and retest.
Here's my thinking; At 60 mph, your fuel requirement is really low.I think the regulator is unable to properly regulate at that low a setting, and eventually the bowl runs dry.
Either that or the pump is sucking air. Could be anywhere on the suction side, all the way to the sender.
And here's the thinking on that; the usual culprit is the rubber line connecting the sender to the main line, at the back. It's high enough to not leak liquid. And as long as the fuel requirement is high, the pump gets enough fuel. On a bypass system some or most of the air will get returned. That's why I recommended a test for that.
But at low fuel requirements, the pump draws mostly air, and sooner or la.....
Now, the line may be new, as stated, but if the line to sender is not secure, this is how the trouble starts. If using a metallic main line, I double gear-clamp those,180* apart. If using AN fittings, you're on your own, cuz I don't use that stuff.I also don't put filters on the suction side, without double clamping.
When single clamping, the rubber hose tends to bunch up right at the screw. I've had them leak there. Double clamping, 180*apart, eliminates that possibility.

It can't be hooked straight to the carb as the pump is rated at about 14psi from memory.
I will check the fuel pressure at highway rpms just free revving it. I'll also check over all the fittings to make sure they are tight, and yes they are AN fittings

Thanks for all the advice.