Vapor Lock

[Chuck]

Now that is something I have not heard in about . . . . 30 years. Vapor Lock! But it seems to have afflicted us twice in one weekend, just in time for the warm weather.

It happened to Ryan on Friday and to me today. Both times after a nice drive getting the GT up to operating temp, shut down, then restart. In Ryans case the restart was after a few minutes. In my case after a couple of hours. In both cases the fuel pressure gauge remained at zero.

I pulled the fuel line off between the pump and the second fuel filter, sucked a bit of gas (that will make your lips tingle), and the problem was instantly solved.

So the question: How do we prevent this nuisance from happening? Why is it happening now? Related to the volatility of the fuel being produced this time of year?

Holley 125 gyrotor pumps. Work great.

The fuel line runs from the pump on the passenger side in front of the engine, joins the left side fuel line at the secondary fuel filter, then to the pressure gauge, and then to the carb. In 2500 miles this has happened only a couple of times before, until this weekend.

The section of fuel line that runs in front of the engine is inside an insluated sleeve, visible in the pics.

Some old pics are attached. The layout is generally the same, although we have a bit more rubber fuel line and a bit less rigid aluminum than shown in the pics.

 

[Randy V]

Chuck - Quite honestly I've never experienced vapor lock with a functioning electric fuel pump...

Is it possible that the vent line to the tank is plugged and you built up a vacuum in the tanks?

Gearotor pumps are among the best and far better than vane style pumps.. If you had a return style regulator, I might have said that it was possibly at fault and routing all the fuel back to the tank. Deadhead regulators don't fail - often - yours may have though.. I would probably start there...

 

[Chuck]

Thanks Randy. I am leaning towards winter fuel vaporizing on warm days. Can't think of any other reason it would do it all of a sudden and repeatedly just when the warm weather sets in.

Yet like you it commented it seems odd with the electric fuel pump. Fuel gauge, when lines are cleared shows good pressure. No problem with the vent.

Noticed another forum suggested adding a bit of diesel fuel to the gas to reduce it's volitility. Had never heard that idea before. I am more inclined to wait a couple weeks until the gas stations sell their summer blends.

 

[Mike Drew]

Isn't your car a Superformance?

Didn't they (at least the early cars) have a reputation for horrible crud in the fuel tanks left over from manufacturing? Could it be that crud is jamming the fuel pump somehow?

 

[Jac Mac]

Sounds like your running a 'Deadhead' fuel line circuit with no return line bleed to the tanks, that means that at low fuel requirement times the fuel gets recirculated within the pump/s & overheats. We had no end of trouble with the TVR until we changed to a full loop setup, the pump was so hot you could barely hold your hand on it, creating its own vapour lock & on a couple of occasions locked the pump up. Only happened in our case when setting on dummy grid for long periods or behind pace car, at full noise there was sufficient fuel passing thru pump to keep it cool, sort of back to front from usual pump issues.

 

[Chuck]

Mike: it is an RCR, so I get the blame for the fuel system. There is a primary filter between the pickup tube and the pump, which I replaced around 1000 miles just to make sure construction debris was not an issue.

 

[Chuck]

Jac: you are right. No return line.

But what I failed to mention is the problem never occurs when the engine is running. It can idle for long time with no problem. It only happened after shut down, then when restarting later. Also the pump did not feel any more warm than surrounding structures. Nonetheless that could well be the problem. Indeed Ryan got it going by alternating squeezing the hoses on the input and output sides of the pump.

Adding a return line would be a huge project requiring removal of the clip to access the tank.

Your point is well taken. My next project will have a return line regardless.

 

[Randy V]

Chuck - Interesting information .... So it would seem that perhaps there may be a need for a check-valve to be placed just aft of the fuel pump (prior to the regulator) to keep the gearotor immersed perhaps?

Also - One could carefully drill into the rear of the fuel tanks just aft of the Spider / Bulkhead, Tap it for a fitting and run the return into the top of the tank. Would be better to put a tube in that would take the returned fuel to the botom of the tank though..

 

[Chuck]

Randy:

I have a check valve between the pump and the pickup tube. It's intended purpose is to prevent the pump on the opposite side from pumping fuel into the opposite tank. An added benefit would be to prevent fuel from draining back into the tank from the pump.

Can't add the tap to my tank because I added the "wings" that extend out beyond the end point of the fuel tank. Those wings conceal the filler tube access. To remove the wings would probably require removing the spider. There is an access hole so I can get to the primary fuel filter and check valve, but drilling a hole would be a challenge.

Hopefully the pictures make more sense than my rambling.

 

[Randy V]

You may want to consider installing yet another Check Valve at the regulator just as added protection.

I'm wondering if heat-soak is percolating the fuel above your current check valve?

RE: Access to the fuel tanks.
I didn't notice the additional bulkheads blocking access to the tops of the tanks..
There is another place.
In the tunnel you can drill into the sides of the tanks to install your fittings there.. You'd obviously need to drain the tanks and use a pneumatic drill - but...

 

[Chuck]

Randy. Good idea re accessing tank from side.

At this point I am inclined to wait and give the local gas stations time to get their summer formulations. I continue to believe that the winter formulations on a warm day may be a big factor in the vaporization. Just does not make sense that the issue would pop up after so many miles on the first warm spell after a cold season.

 

[EGLITOM]

Chuck

THe strange thing is that you have two fuel pumps and if one gets hot it is the one which has been activ before you stopped the engine.
Did you try to start the engine with the second (other side fuel pump ) as well ? if so and it did not start as well, i rather tend towards an issue with regulator or heat related issue of the carb bowls.

Also the issue could be the location of your check valves. I think to remember that you have to modify them to overcome theire closing pressure and to enable the pumps to provide fuel at all. I have placed mine after the pump, because pressurised liquid will overcome them always easier than trying to suck through them.

Also i´m not quite shure if the line from the pickup to the pump over the check valve has a steady incline or if it is higher at some point before the pump than the inlet of the pump. THis would or could create a kind of "sack" which not can be purged out.

Thanks
TOM

 

[Chuck]

May have found the problem. Could a faulty needle seat on the secondary that permitted fuel to rapidly leak out of the vent hole thus relieving the pressure in the fuel line explain it? With a hot engine and no pressure on the fuel, it would seem vaporization is more likely, thus explaining the 'vapor lock'.

Had planned to go for a drive this evening - first since the Sunday 'vapor lock' issue. Did a pre flight check and noticed when the fuel pump was turned on fuel was draining rapidly from the secondary float chamber.
Never saw that one before. Indeed that was a large puddle of gas in the intake manifold valley. The problem was the secondary needle seat has become loose. Tightened it down, re set the float levels, and leak was gone.

Before fixing it, noticed that when the fuel pump was shut off the pressure immediately dropped to zero. Normally it holds the set pressure for a pretty long time.

Guess I will need to take it out on a hot day, shut it down and restart it. But I think this might be the problem. It helps explain why the problem appeared so suddenly after so many miles.

Am I crazy, or is this a reasonable theory??

 

[Randy V]

It still sounds like your Check valve is not working and all the fuel is draining back into the tank..

Might have a spec of crud in the seat of the Check valve or it's just broken..

If the check valve were leaking, it should hold pressure..

If your secondary float valve were malfunctioning - it would more than likely flood over.. It would not empty the fuel line that was below the level of the carb - it would also lose pressure - although the carb's float does a poor job of holding pressure for very long typically..

The flooding alone would make the car difficult to start....

 

[Jim Dewar]

I experienced the same problem the 1st summer after my build. I solved it by installing the Holly fuel pump you are using (quiet - tossed out the Holley Blue)but in an area with less heat and lower by the tanks. I also installed a Birch wood spacer between the intake and carb (assuming you are using a Holley carb.) I don't know which solved the problem but likely the Birch wood spacer.

 

[Jonathan Strain]

The pumps do not like to work as lift pumps. It is more of a case of loosing its prime than vapor lock. I have the same issues with my pumps. Mounting the pumps lower would help but there are not a lot of low places to put the pumps on the RCRs.

 

[Ian Anderson]

The pumps do not like to work as lift pumps. It is more of a case of loosing its prime than vapor lock. I have the same issues with my pumps. Mounting the pumps lower would help but there are not a lot of low places to put the pumps on the RCRs.

If that is the case then make sure you have a short length of pipe and a piece of cloth to wrap around it (to seal against the tank fill area) and blow into the tank (at filler) to slghtly pressurise the system.

This worked well when I first primed my system (running Facit pump that would not prime by itself)

Ian

 

[Bill Musarra]

Ian,
A blow job on your 40!!!! Thats something I would like to have seen. I know we love these cars but really:lipsrsealed::laugh:

Bill