Vapor lock and Percolating Carburetor

[JoeKan]

I've put my 68 back together and its been a blast driving but now whenever I take her out and stop somewhere and shut it off, she don't want to start up again. I talk to a buddy of mine and he said its either vapor lock and/or the gas in the carb is percolating. From what I've found on the net, I tend to agree. What I can't find is how to fix it? It's gotten to the point that I can't take her out anymore because if I shut her off, I'll have to wait an hour before she fires up again.
Any help will be greatly appreciated.
Joe

[Tom]

Plastic carb spacer.

[geezer#99]

What carb?
Does it crank over easily?

[AussieinNC]

What carb is on it?

If its a Quadrajet, did you install the thick base gasket?

Fuel pump is original manual type ro electrical?

[JoeKan]

It's the original carburetor on it. same as the fuel pump.

[Dead Parrot]

If the heads and intake have provisions for an exhaust crossover under the carb, make sure the riser valve(if still equipped) isn't stuck shut or partially stuck.

2nd the thought on the thick base gasket.

Exhaust type?
Fan type? Number of blades?
Still have the fan shroud?

[geezer#99]

Originally Posted by JoeKan

It's the original carburetor on it. same as the fuel pump.

And does it crank slow or fast?

[JoeKan]

Originally Posted by geezer#99

And does it crank slow or fast?

It cranks fast but I think that is normal. It also has been backfiring too. Went to start it the other day and sounded like a gun going off! And when I take the foot of the gas when coming to a stop sign or red light, it will backfire too.
To be honest, I'm stuck on stupid when it comes to carbs.

[JoeKan]

Would a wood carb spacer fix the problem? Of if the gas is percolating in the gas line, what if I change the gas line to rubber?

[geezer#99]

Rochester carbs don’t usually have percolation problems.
A wood spacer would work. Try one.
The backfiring can be caused by a lean carb and lack of initial timing.
Are you using a choke when starting it?
What’s your initial timing?

[Bimus]

The 68 pickup has the fuel tank behind the seat and it's higher then the fuel pump and fuel free flows to the pump most of the time so the pump is pushing fuel to the carburetor but is pulling air from some where and vaporizing the fuel .

[JoeKan]

Originally Posted by geezer#99

Rochester carbs don’t usually have percolation problems.
A wood spacer would work. Try one.
The backfiring can be caused by a lean carb and lack of initial timing.
Are you using a choke when starting it?
What’s your initial timing?

Yes, I choke it when I start it. I don't know what my timing is.

[geezer#99]

Originally Posted by JoeKan

I don't know what my timing is.

Likely the source of your problems.
Maybe it’s time to learn about timing!

[JoeKan]

Good point and well taken. Thank you

[geezer#99]

Lots of vids on the process.

https://www.youtube.com/watch?v=AhV9yMuUEok

[AcampoDave]

I live where it gets hotter than hell, and do have that percolation problem. (Mine is an Eddy carb which is already known for that.) I have the plastic spacer, (I probably need a pressure regulator too) but mine will still start if I floor the pedal as I'm cranking it and let off just when it fires up. Essentially, the engine is flooded when that happens and I don't think using the choke would be helpful in that situation. I do agree with Geezer about the timing but mainly wanted to suggest you stop choking it when that happens.

[garyd1961]

Have you checked the firing order, could have the sparkplug wires crossed. Mine will be hard to start after shutting it off and sitting about 30 minutes but it has never backfired. I believe mine is a combination of heat under the hood from headers and the electric choke closing while the motor is still hot.