Vapor lock with our modern fuel

[60FlatTop]

I believe that science and engineering skills were advanced enough to be able to build a car and get it out of a showroom, even on a hot day, with enough reliability to get the customer to part with their money. Heck, only 50 years later they put guys on the moon.

"I" didn't believe the clothespins I saw did anything. But many do.

 

What I do see is a lack of diagnostic tools. Maybe a gauge tee'ed at the carburetor. That would be a good indicator of the vacuum tank operation. Whatever the height of the normal operating fuel level above the carb can be measured in feet of head, nominally 18", give or take a little. Figure gasoline with a specific gravity of0 .7, that puts 1 PSIG at the feed. A mix of ethanol will vary that some, but the first test would be telling enough. I would use a manometer to measure or just clear tubing to the point where the tank level was supposed to be. Then run the car under the problem conditions. If I found the pressure to be less than I expected I would look for vacuum reducing the pressure through a leaking vacuum tank valve. If the pressure was greater (from the fuel boiling?) I would look for a plugged atmospheric vent. Those appear to be the two basic scenarios. If more questions arise I would devise another test. But my anticipation would be a pressure, during operation, equal to the feet of head for the specific gravity.

 

My other anticipation is that someone has measured that and can share what they found using a "tool". In some circles the use of tools make great differentiation.

 

That's why I don't believe a lot of those old guy stories. They don't use tools.

Bernie

[Dave Young]

All good on the Chandler now.  I had a bowl temperature of 190 last week, before putting the 2nd version heat shield on. Now, the bowl temp is 85, while the the exhaust down-leg is 400, only 4" away from the bowl.  The heat shield is doing its job.  I really doubt that even the best fuel could take that much heat.  This is a retrofit updraft carb crammed into a tight spot.  Thanks for all of the advise.

[DavidMc]

grimy:   My scanner has "died" so I can't post a sketch however the circuit for a bypass electric pump is simple.  A fuel line from  a T in the line from the tank before that vacuum tank to a T right at the carburetor with the low pressure electric pump in that line.   A one way valve in the line from the vacuum tank to the carburetor to avoid the pump feeding back into the vacuum tank.  I also fitted a one way valve in the bypass line to prevent the vacuum tank from feeding back through that line to the tank.  Its debatable whether that one was necessary.

I did not use a pressure regulator at the carburetor and it did not flood against the electric pump pressure however it was probably very close to doing so,  so I fitted a soft tip to the cut off needle replacing the original brass on brass.  That seemed to work OK (more on that later)

The logic behind all this was to be able to start the electric pump while driving , at the first sign of vapor lock.   The one way valves I used were of the type used in racing cars to cut off fuel supply in the event of roll over.  They were a simple ball and spring type.  There might be something better out there but if so I could not find it.  After that I sold the car to a friend.  It ran well for a while and then it the owner reported it seemed to be intermittently starving for fuel, stopping, refusing to start but in between these episodes it ran fine.  It was not vapor lock, it occurred when the weather conditions were very cold.  All the usual fuel and ignition checks were made with nothing untoward found..  So we speculated that the one way valve in the line from the vacuum tank to the carburetor  may have been restricting flow, intermittently.  So the next step, by the current owner, was to remove the 2 one way valves  and use the manual valve at the base of the vacuum tank to prevent the pump back feeding and another  in the  bypass line to prevent the vacuum tank feeding back to the tank via the bypass.   However the intermittent problem continued .  It was finally discovered that the soft tipped cut off needle that I had fitted to the carburetor was sticking closed cutting off the fuel supply.     The original cut off needle was reinstalled and it continues to work fine without a pressure regulator on the rare occasions that it is required to operate with the pump    That is how the car is at present and the owner is happy with that.

It is possible that the originally conceived arrangement with one way valves might work but it is a concern that the one in the line from the vacuum tank might give problems whereas a manual set up has no such potential.  

Sorry for the long winded explanation which I hope makes sense.

 

[Dave Young]

Here are some pictures of the heat shield.  That Zenith 63 is only 3/4" away from the exhaust down-leg.

[Grimy]

The only thing I can suggest for possible improvement is to make a new, longer feed line from the vacuum tank to the carb and make a vertical loop in it to minimize possible vaporization of fuel enroute to the carb.

[Spinneyhill]

28 minutes ago, Grimy said:

The only thing I can suggest for possible improvement is to make a new, longer feed line from the vacuum tank to the carb and make a vertical loop in it to minimize possible vaporization of fuel enroute to the carb.

 

I have often wondered about whether an air lock in the top of the loop can occur and restrict or stop flow.

[Grimy]

2 minutes ago, Spinneyhill said:

have often wondered about whether an air lock in the top of the loop can occur and restrict or stop flow.

Good point.  I don't know...has anyone had experience?

 

In that particular case, I'd be inclined to put the loop forward of the carb, where it would receive constant fan-driven air.

Edited November 13, 2017 by Grimy
added another thought (see edit history)

[Dave Young]

Yeah, that fuel line is on my list for this weekend.  I hate the way it looks, too.  The car is running beautifully now.  That goofy looking air filter is a recent addition and I plan to make a metal enclosure around it.  I found the car to running far too rich without the heat blasting on the carb, and reduced the jet sizes on both the main and power valve.  This is a great Orphan car and we drive it quite a lot.  The poor little Model A seems jealous when we head out for the day in her.

[Marty Roth]

Years ago we installed a modern fuel filter in line to the carb on the '37 Roadmaster. It has a third port as a relief valve and I have tis connected to a line which runs back to a nipple on the fuel filler pipe at the rear of the car.

 

With this return line in place, fuel does not sit still over the heat of the engine.

 

We also have a phenolic additional thick gasket (from CoolCarb Technologies) under the carb of the '41 Caddy, and plan to install one on the '37 Roadmaster

 

Look at www.coolcarb.com 

 

[Dave Young]

Thanks Marty.  I'll look into that gasket.