Vapour Lock Issue

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EXcappa

EXcappa

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Hi All,

I have been trying to sort vapour lock issues in my fuel system.
I currently have
1/2" supply and return line back to tank
Holley billet bypass regulator
Claysmith mechanical fuel pump
Tank venting has checked out fine

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.

What else can I do to rectify the problem?
The fuel lines and carby get warm but not overly hot to touch.
Thanks.
 
Are you sure it's fuel? Is it sporadic? AND, does it fire right back up immediately?
 
If you're running a square bore carburetor on a dual plane, this 5/16" thick gasket will help insulate the carb from some heat. I've had good luck with them...

http://www.manciniracing.com/hein4sqboe.html


Or find a similar one for your set-up if it's a different intake like open plane or spread bore. Find one that's at least 1/4" thick...
 
60 mph cruise, cough and die, does not sound like vapor loc. Nor does it sound like a gradual loss of fuel delivery.
At this speed and throttle setting, the carb is running on the low-speed circuit. I agree that the cough may indicate a very lean condition. Since it's ongoing, and you didn't mention a hard restart with long cranking times, I would suspect a problem in that circuit; possibly an intermittent obstruction in the idle well. If you can't find it there, I would check the return line for air bubbles, which would point to air being sucked up by the pump somewhere.But I really don't think it's air. Water?maybe.
 
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.
 
Had a similar problem while driving a 340 73 RR I bought in Albuquerque and drove back to CA. The car wouldn't go more than 60 and losing power. I stopped and changed the fuel pump on the side of the road. Then, I thought it was vapor lock, the car was sputtering and died in Winslow. Got it going again and it happened again. Barely made to Flagstaff. A mechanic looked at and couldn't figure it out. I looked at it again and discovered cracked vacuum hoses. I changed the vacuum hoses and drove the rest of the way problem free at 85 mph. The RR has a Quadrajet carb.
 
Your symptoms are more like vacuum lock than vapor lock..

I know you said the vent was fine,, but humor us by taking it for a 60 mph cruise with the gas cap loose..

cheers..
 
What about a clogged fuel filter?

Just another quick cheap thing to check...
 
Oh,boy. Ok you need to prove it's a fuel issue. A 30 minute delay, could be a vent/vacuum problem, or an electrical issue, or a carb issue.
So, as inertia suggests, run with the gas cap loose. If the problem persists, pull over and immediately pop the air filter house off. Stare down the primary bores and pump the throttle a couple of times. Slow,long strokes, all the way back. You will be looking for a long continuous stream from the accelerator nozzles. If it's there, there is fuel in the bowls. Next will be a spark test.Sometimes the ECU,or the MAG trigger quits when it gets hot. I used to carry spares in the glove box for just such times.
 
Also keep in mind that heat (even though not excessive) can cause electrical issues that can produce popping and sputtering.
Verifying a spark when this stalling and no start condition exists might be a good clue.

Heck I have even seen the connector for the distributor cause stalling and not starting until the actual connector cooled down from normal engine temps.
Just crimping the connector a little fixed the two I saw do this.
 
inertia said:
Your symptoms are more like vacuum lock than vapor lock..

I know you said the vent was fine,, but humor us by taking it for a 60 mph cruise with the gas cap loose..

cheers..
Click to expand...

I have tried driving with the cap off and it made no difference
 
AJ/FormS said:
Oh,boy. Ok you need to prove it's a fuel issue. A 30 minute delay, could be a vent/vacuum problem, or an electrical issue, or a carb issue.
So, as inertia suggests, run with the gas cap loose. If the problem persists, pull over and immediately pop the air filter house off. Stare down the primary bores and pump the throttle a couple of times. Slow,long strokes, all the way back. You will be looking for a long continuous stream from the accelerator nozzles. If it's there, there is fuel in the bowls. Next will be a spark test.Sometimes the ECU,or the MAG trigger quits when it gets hot. I used to carry spares in the glove box for just such times.
Click to expand...

Thanks I will check the fuel squirt stream next time it stalls.
Not sure about the electrical side of it...it has an MSD set up
 
Pscuda65 said:
Had a similar problem while driving a 340 73 RR I bought in Albuquerque and drove back to CA. The car wouldn't go more than 60 and losing power. I stopped and changed the fuel pump on the side of the road. Then, I thought it was vapor lock, the car was sputtering and died in Winslow. Got it going again and it happened again. Barely made to Flagstaff. A mechanic looked at and couldn't figure it out. I looked at it again and discovered cracked vacuum hoses. I changed the vacuum hoses and drove the rest of the way problem free at 85 mph. The RR has a Quadrajet carb.
Click to expand...

Everything like lines, hoses, holley etc are all brand new.
 
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.

Thanks for all the replies so far.
 
That 1/2" fuel line is a LOT of fuel weight for the pump to move. Just kinda thinkin out loud.
 
im a mechanic, what size motor you runnin and give us a run down on your spark distribution and carb type? also as soon as it does that check for gas down carb?
 
blackbitch said:
im a mechanic, what size motor you runnin and give us a run down on your spark distribution and carb type? also as soon as it does that check for gas down carb?
Click to expand...

Its a 565hp 360/416 stroker.
Here's the build if you want to have a read, made decent power through the crappy headers. It now has a set of pipes 4into1 1.75" stepped to 1 7/8"
http://www.aussiev8.com.au/chrysler-valiant/65980-chrysler-360-stroker.html

Its a custom built 750dp carb, was originally intended for 360 cubes but then changed plans and stroked it otherwise 950 probably would have been a better size
http://www.zokracecarbs.com.au/
The carb is super responsive.

There were a few small electrical issues that were sorted on the dyno, Not real sure about the spark distribution but as previously mentioned it runs fine when cool.
Also runs fine around town when warm.....it just has issues when warm and highway driving.

Love this motor but, it will smoke street tyres at 60mph
 
GEO said:
Doesn't happen to have an orange ignition control box?
Click to expand...

Not too sure on that.
From memory it has an MSD distributor, MSD control box under the dash and the coil is under the dash also.
Ill have a good check tomorrow to see exactly what they are
 
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, and including the pump and regulator.Unless it's sucking air right before the pump.
 
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