Vapor Lock

[Old Henry]

With the tiles on the space shuttle being able to keep the heat on one side oNly,you think there would be some modern material that could be used to insulate the fuel pump and carb from the engine and manifold,
It's easy to insulate the fuel line ,but no so the pump and carb,
I have made a small air scoop that fits in beside the radiator and takes air from in front of the radiator via a 1-1/4 hose to the fuel pump,this helps ,also have a spacer under the carb,
But in 39c the fuel will still vaporise.
Any one work for NASA who get get us one of those tiles?
Lawrie

Although there are ways to keep the mechanical pump a bit cooler while running (fuel return line as G.M. has done, air ventilation as Lawrie has done, remove the hood in front of the radiator to let air flow over the radiator to cool the whole engine compartment more) none of that makes any difference nor gives any benefit when you park the car in the sun, turn the engine off, and run into the store to grab something. All of that cooling goes out the window (or up the chimney in this case) and the heat of the engine, regardless of how many funny lick spacers one has under the carburetor, is going to heat the whole compartment, including the mechanical pump, above the boiling temperature of the new gas and, when you come out and start up the engine, there is only going to be air in the mechanical pump and it ain'ta gonna pump. That's where the electric pump comes in to fill the mechanical pump with liquid fuel to start it pumping again. Capish?

OK Alan I get your point .The electric pumps making up for the Mechanical one not doing its job ,set up a vacuum gauge at the tank end and check for leaks .Also the reduction in performance of a mechanical pump pulling fuel through a Artex pump has to be considered ,Tests ? Ted

My mechanical pump pulls through the Airtex when shut off just fine.

Fuel boiling in the float bowl is a pretty good clue that it's fuel related, but only a true expert can say for sure.

Best true test for vapor lock: Keep a gallon of water with you. When the engine dies open the hood and pour a quart or two slowly on the mechanical fuel pump. Then, get back in and start it up. If it starts, you know it was vapor lock. I hung in there for total authenticity not wanting to put in an electric pump but I got tired of the engine dying (way too often at very inopportune moments) and having to get out, open the hood, and pour water on the mechanical pump to get it going again. So, I bit the bullet and put in the electric pump.

 

[tubman]

I chased what I thought was vapor lock on my '51 for a couple of years. Even went so far as to install an electric pump. I finally found out it was a slight leak at the rim of the sediment bowl. I evened it out with wet-or-dry on my surface plate, installed a new gasket, and the leak was fixed. (I removed the electric pump a few years later, and have not needed it since). Surprisingly, cork bowl gaskets seem to work better and last longer than neoprene ones; I have no idea why.

 

[butchbov]

ladies & gents here is the answer to your dreaded vapor Lock. This is the Davis Rods Vapor Lock Eliminator kit & is available for one easy installment of $19.95 + S&H. What you get is 8 clothes pins made from the finest Brazilian hardwood & instructions on how to attach them to your fuel line.

 

[ford38v8]

Henry put the fuel pump in the worst possible location. Besides being at the top rear against the firewall with no air circulation, he opened a direct channel from the valve chamber to the fuel pump diaphram to insure it received all the heat it needed to produce vapor lock. Insulating gaskets and phenolic spacers be damned, that direct passageway for heat is still there.

For those who, as our Old Henry was, not thrilled about installing a modern electric fuel pump to combat the problem, there is a viable solution that could easily have been done by anyone at any time back in the day:

(G.M. has done some homework to confirm that this works.) I remember one old timer who said he used an original hydrostatic gage siamese fuel line to make this very modification. Providing a small return line from pump to tank will effectively keep the fuel flowing cool so as to not flash to vapor. This has been shown to work while the engine is running, but sadly, it's still a problem when you shut down unless you open the hood.

Something to be said for Hot Rodders with no hoods!

 

[tubman]

Funny thing about hoods; when I was having my problems, I got into the habit of leaving the hood up when parking it on hot days. I got a lot of funny looks (stock 8BA), but it always started.

 

[Old Henry]

Funny thing about hoods; when I was having my problems, I got into the habit of leaving the hood up when parking it on hot days. I got a lot of funny looks (stock 8BA), but it always started.

I used to do the same thing. Worked for me too. But, alas, too embarrassing for me (yes, I do have my limits). Went to the electric pump.

 

[FlatheadTed]

In the case of Tubman a vacuum check back at the tank out let would tell you if you have leak down . he also shows that you can mistake other faults for VL .
when you park the car in the sun, turn the engine off, and run into the store to grab something. All of that cooling goes out the window (or up the chimney in this case) and the heat of the engine, regardless

Henry one would assume the carb had completely dried out .during that short visit to the shop ?? a half a bowl of fuel will start the car regardless of the pump.

 

[Old Henry]

In the case of Tubman a vacuum check back at the tank out let would tell you if you have leak down . he also shows that you can mistake other faults for VL .
when you park the car in the sun, turn the engine off, and run into the store to grab something. All of that cooling goes out the window (or up the chimney in this case) and the heat of the engine, regardless

Henry one would assume the carb had completely dried out .during that short visit to the shop ?? a half a bowl of fuel will start the car regardless of the pump.

Yes, it may start. But when that little bit of fuel left in the carburetor (that hasn't boiled out) runs out, the engine will die and not start again. I had that happen at the top of Pike's Peak before I figured out vapor lock. I thought I'd pull my car quickly in front of the elevation sign for a quick picture then get out before some ranger came by to harass me. Started the car up and got in place for the photo but then the engine died and would not start for what seemed like an eternity while the ranger harangued me up and down and finally threatened to call a tow truck up from Colorado Springs to tow me out of there. (He had a truck and I had a strap but he wasn't about to help, just yell. I finally got someone else to tow me out and head me down the mountain to get it started.) It was on my way home that I tried pouring the water on the fuel pump after the engine died and had the engine start right up that I figured out that we'd had vapor lock problems the whole trip. There were many other sudden deaths that were nearly as embarrassing before I finally installed the electric pump.

Stuck in the no parking zone with vapor lock:

Not a happy camper!

 

[FlatheadTed]

sounds like you were in a mess of problems there Henry .
Something to try .A vacuum gage can be placed on the rear end of the fuel line ,air tight ,then the motor started ,when the vacuum reaches maximum shut the motor of, it should hold vacuum for at least 2 min this test can be done at the pump flex line or If the fuel line has been cut along its length any were then I suggest at the rear is best .Ted

 

[Old Henry]

sounds like you were in a mess of problems there Henry .

I could fill the screen with funny stories of my vapor lock before coming to understand it and deal with it. I probably had more than most because of where I live and drive. I live at 5,000 feet and regularly drive up to 10,000 feet and more. Higher altitude = lower air pressure = lower boiling temperature of everything including gasoline = more vapor lock.

 

[ford38v8]

How about a discussion of the actual mechanics of Vapor Lock? I'll start and let's see where this goes? Off the top of my head from real world experience, without benefit (?) of scientific testing:

Heat begins the vaporization of fuel in the pump chamber>
Vaporization raises the pump chamber pressure>
Higher chamber pressure approximates the diaphragm spring pressure>
Shorter diaphram stroke drastically reduces liquid fuel flow to carb>
Vapor overloads the only relief of same at the carb's needle valve>
Carb begins to starve, engine bucks>
Without liquid fuel, pump gets uber hot, engine dies for lack of fuel>
With the hood open, pump cools in 15 minutes>
Do it all over again.

Does anyone have an alternate explanation?

 

[G.M.]

How about a discussion of the actual mechanics of Vapor Lock? I'll start and let's see where this goes? Off the top of my head from real world experience, without benefit (?) of scientific testing:

Heat begins the vaporization of fuel in the pump chamber>
Vaporization raises the pump chamber pressure>
Higher chamber pressure approximates the diaphragm spring pressure>
Shorter diaphram stroke drastically reduces liquid fuel flow to carb>
Vapor overloads the only relief of same at the carb's needle valve>
Carb begins to starve, engine bucks>
Without liquid fuel, pump gets uber hot, engine dies for lack of fuel>
With the hood open, pump cools in 15 minutes>
Do it all over again.

I see lower fuel pressures right after the pump when the vapor lock starts, down in the 1 1/2lb range. G.M.
]

 

[V8COOPMAN]

I see lower fuel pressures right after the pump when the vapor lock starts, down in the 1 1/2lb range. G.M.

And, that sounds understandable, George. As you realize, you can have positive PRESSURE with a vapor, or with an in-compressible liquid. In the case where the liquid turns to vapor (because of too much heat), the VAPOR pressure does nothing to move liquid fuel toward the carburetor. Almost like breathing IN TO, and OUT OF a balloon....no work is accomplished. DD

 

[FlatheadTed]

maybe Someone should post here a accurate scale of what temperature each fuel company's fuel will turn to vapour ,this possibly could be got from there web sites . I would say its a lot higher than what you think it is .Ted

 

[ford38v8]

maybe FlatheadTed should post here a accurate scale of what temperature each fuel company's fuel will turn to vapour ,this possibly could be got from there web sites . I would say its a lot higher than what you think it is .Ted

Call & raise.

 

[V8COOPMAN]

Seems like I remember G.M. doing some testing and finding the boiling point (of the fuel) at just under 130 F. DD

 

[ford38v8]

I'd sooner trust G.M.'s data than any you'd find from a fuel company website.

 

[FlatheadTed]

The average flathead runs at 160 to 180 at 130 F why are the cars running at all ??

 

[Old Henry]

maybe Someone should post here a accurate scale of what temperature each fuel company's fuel will turn to vapour ,this possibly could be got from there web sites . I would say its a lot higher than what you think it is .Ted

Problem with that is that boiling temperature depends on the ambient atmospheric pressure which varies with elevation and weather. So, the boiling temperature of any particular gasoline is not a constant that could be reported as I mentioned before:

I probably have more than most because of where I live and drive. I live at 5,000 feet and regularly drive up to 10,000 feet and more. Higher altitude = lower air pressure = lower boiling temperature of everything including gasoline = more vapor lock.

 

[Old Henry]

I'd sooner trust G.M.'s data than any you'd find from a fuel company website.

G.M found the boiling temperature of the gasoline in his settling bowl on a particular day at sea level (or close) to be 140-145 here: http://www.fordbarn.com/forum/showthread.php?t=61323&highlight=boiling+gasoline&page=2

But that boiling temperature would be much lower at my elevation and would be different for other gasolines and on other days. So, impossible to predict precisely.