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My car developed a vapor lock problem a couple years ago. This was after several years of ownership with absolutely no vapor lock issues at all.

Driving the car for even short distances (5 miles) results in a no start situation within 30 minutes of shutoff. This occurs in all seasons and ambient temps. While the car is running, there is no hint of trouble. I can drive 100 miles or more without incident but once the car is turned off, within 30 minutes, the car will not receive fuel. It will use up whatever is in the bowl and then not start for several hours after fuel returns to liquid state.

The fuel pump was replaced with zero effect. The entire fuel line from the pump to the tank was also replaced just in case there was a leak where air was being drawn into the system. This had no effect on the problem.

The car is not overheating. The radiator is full and not boiling over. The needle on the gauge barely gets off the first E in TEMPERATURE. The water pump was replaced before this problem developed and the gauge actually reads lower on average than it did before the replacement.

It had no trouble the first few years I owned it then started this crap.

I read that some modern fuel blends can boil at temps as low as 100F. That's crazy.

Anyway, I decided to install a clear fuel hose between the pump and the carb to get a at what's going on.

So, here are a few videos of all whole mess.

Here is the hose after installation with the engine running. After clearing out the air trapped in the line during installation, the hose is filled completely with fuel and no vapor bubbles.

https://www.youtube.com/watch?v=NY27d7WmbYw

Here we are after a short 5 mile drive on local roads . The outside air temperature is only 65 and the car itself doesn't appear to overheat. The radiator is full and the overflow tank isn't being loaded up with coolant.

Notice the air pockets and bubbles when I rev the engine.

https://www.youtube.com/watch?v=WPtPh49gr4w

After sitting for 30 minutes, notice how the fuel line is devoid of fuel almost entirely.

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

I installed a temporary fuel jug under the hood and disconnected the line to the tank in order to rule out problems with the supply line and/or the fuel pickup inside the tank. I experienced the same problem after a short , 5 mile drive.

What can be done about this situation? My car has no AC and is thus equipped with a fuel pump that does not have a return line. It's been suggested to me that I install the ac fuel pump and run a return line back to the tank. Will this help? It appears that the fuel is vaporizing between the pump and carb.

Also, dumping cold water on the fuel pump does not instantly cure the problem.

Another suggestion is to install an electric fuel pump. Have any of you done this? If so, what are the details? Why did you do it?

Otto Skorzeny wrote:My car developed a vapor lock problem a couple years ago. This was after several years of ownership with absolutely no vapor lock issues at all.

Driving the car for even short distances (5 miles) results in a no start situation within 30 minutes of shutoff. This occurs in all seasons and ambient temps. While the car is running, there is no hint of trouble. I can drive 100 miles or more without incident but once the car is turned off, within 30 minutes, the car will not receive fuel. It will use up whatever is in the bowl and then not start for several hours after fuel returns to liquid state.

The fuel pump was replaced with zero effect. The entire fuel line from the pump to the tank was also replaced just in case there was a leak where air was being drawn into the system. This had no effect on the problem.

The car is not overheating. The radiator is full and not boiling over. The needle on the gauge barely gets off the first E in TEMPERATURE. The water pump was replaced before this problem developed and the gauge actually reads lower on average than it did before the replacement.

It had no trouble the first few years I owned it then started this crap.

I read that some modern fuel blends can boil at temps as low as 100F. That's crazy.

Anyway, I decided to install a clear fuel hose between the pump and the carb to get a at what's going on.

So, here are a few videos of all whole mess.

Here is the hose after installation with the engine running. After clearing out the air trapped in the line during installation, the hose is filled completely with fuel and no vapor bubbles.

https://www.youtube.com/watch?v=NY27d7WmbYw

Here we are after a short 5 mile drive on local roads . The outside air temperature is only 65 and the car itself doesn't appear to overheat. The radiator is full and the overflow tank isn't being loaded up with coolant.

Notice the air pockets and bubbles when I rev the engine.

https://www.youtube.com/watch?v=WPtPh49gr4w

After sitting for 30 minutes, notice how the fuel line is devoid of fuel almost entirely.

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

I installed a temporary fuel jug under the hood and disconnected the line to the tank in order to rule out problems with the supply line and/or the fuel pickup inside the tank. I experienced the same problem after a short , 5 mile drive.

What can be done about this situation? My car has no AC and is thus equipped with a fuel pump that does not have a return line. It's been suggested to me that I install the ac fuel pump and run a return line back to the tank. Will this help? It appears that the fuel is vaporizing between the pump and carb.

Also, dumping cold water on the fuel pump does not instantly cure the problem.

Another suggestion is to install an electric fuel pump. Have any of you done this? If so, what are the details? Why did you do it?

On my Toronado, the fuel pump has a return line that travels to the very back of the car and sits on top of the fuel filler. This should help reduce the chances of getting vapor lock. It could also be a good idea to get heat shields for the fuel lines if they are near anything hot (boiling point for gasoline could be as low as 140 degrees Fahrenheit and the normal temperature for an engine ranges between 190-220 degrees Fahrenheit).

I can tell that the return line works in my case because I can see and smell the vapors exiting the tube near the filler.

Yes, the air conditioned equipped '66s have vapor return lines. The non AC cars don't. Maybe they changed it on later models and put return lines on all cars. My car is a non ac car.

I've considered installing an ac fuel pump and running a line back but its a royal pain in the neck since the lines are all inside the frame rails except for the 4 foot section of steel tube under the passenger door.

Insulation on the 8 or 9 inches of exposed rubber line between the pump and frame rail didn't help

I’ve not experienced this before which leads me to believe it’s more about the fuel itself. Can you get non ethanol gas where you are? Or maybe try mixing in half race fuel or avgas.

I have an in line electric pump on my 51 Caddy in addition to the mechanical pump. I installed it originally for the flame throwers but I use it to prime the carb after it has been sitting for extended periods. It works great. Just be sure to get the low pressure (4-7 psi) type.

There are a handful of places around that sell 90 octane non-ethanol fuel but not close by in metro Atlanta. At 9mpg it doesn't make sense to make special trips in the Toro to get it.

I too have thought it might be a change in the fuel but who knows these days? The '56 Cad runs fine on the same crap.

The Olds FSM says the mechanical pump is supposed to be 7 3/4psi to 9psi. Should an electric one be less than that?

I think the pressure on electric pumps is either high or low. Any that are for carbureted engines should work.

Hi Otto,

do you still have this problem?

Martin

Short answer, yes.
Long answer, Sort of.

I've been working on it all summer. I'll try to give you the short version.

Numerous tests ruled out everything from the fuel pump back. It seems that the carburetor is getting extremely hot after shutdown. It appeared that the fuel between the carb and pump was also getting too hot, vaporizing, and had no place to go.

I installed a fuel pump for an ac car which has a fuel / vapor return line and I installed a return line all the way back to the fuel tank.

This helps tremendously but is still not enough. This allows vapor to be purged at the pump. It also allows hot, excess fuel to be pumped back to the tank while being refreshed with cold fuel from the tank.

So far, this has enabled the car to start and run and be driven after shutdown. It's obvious that the car knows something isn't right because I usually have to push my foot down and burn off or purge all the hot fuel under the hood and refresh it with cold fuel. After a few seconds or minutes, the fresh cold fuel is flowing and the car runs and drives normally.

Just a few minutes ago, however, I attempted to start it after sitting for 30 minutes after a drive. No dice. Absolutely no fuel in the carb and none nothing coming from the pump when I disconnected the line at the carb.

Why is it getting so hot? Gauge works and stays in the low range, no water boils out of the radiator.

Someone suggested a lean burn condition. The carb was rebuilt by Daytona Parts who have built many carburetors for me and friends without any problems. This problem existed prior to the rebuild and persisted afterwards with no change.

Daytona installed the correct Toro 425 jets in it as it had jets for a 300 installed. It seems unlikely that both setups would be set too lean.

Timing and everything else has been checked.

Have you adjusted the idle air mixture? That can cause excessive heat too. Just a thought.

I may give that a shot although I trust Daytona when it comes to rebuilding carbs. They run them on a test engine and adjust them before sending them out. They've done a half dozen carbs for me personally as well as for friends and they've all been bolt on and turn the key.

Since this began prior to the carb rebuild it seems unlikely that it would be too lean before and after.

Will the idle mixture adjustment on the Q Jet affect the mixture through all circuits?