vapor lock...just curious

cuzncletus

cuzncletus

Senior Member
My 39 with a 53 engine has a tendency to vapor lock (I think), preventing easy restarts when it's hot. This is particularly true when I'm forced to use 10% ethanol fuel. I'm going to reroute the fuel line away from the driver's side head, easy enough and hopefully will cure the problem. But I had this thought: If a vapor lock is caused by a bubble forming in the line where the gas boils, then fuel being unable to get past the bubble, would removing a line from the carb and venting the gas into a container (bottle) allow the bubble to be pushed through the system?
 
Sounds logical and worth a try. I took the 52 Merc on it's longest drive yet back on a hot day in August and did not have a problem on hot starts. I find I always have to give a couple of pumps on the accelerator pedal before hitting the starter button. Without doing that it won't start.
 
Vapor lock in the fuel system is something that has plagued the flat-head Fords since their inception. To a minor degree all vehicles have suffered from the same problem, however, not as common as the Fords.
Aside from the problems that the modern unleaded/ethanol based fuels cause, motorists have been dealing with with the vapor lock issue in various ways since 1932. The hot setup that was touted by many people during the '40's/50's was to put wooden cloths pins along the fuel line from the pump to the carb., the thinking being that this would draw the heat out of the fuel line... Wrong.
The big problem with the flat-head Fords is the fuel delivery system, i.e. a fuel pump and fuel line located on top of the engine, in lieu on the low side of most other engine blocks.
A second factor is low fuel delivery due to the fuel pump push rod being worm and the fuel pump mounting stand mounting ears being bent up from years of use. Think about it, how many of you have removed the fuel pump mounting stand and checked the base for warpage.. Think about it. A straight-edge across the base and a file can solve a big problem very quickly.
The simple fix to break a vapor lock on a hot summer day is to add an electric fuel pump, mounted as close to the fuel tank as possible, use a toggle switch that can be tuned on or off at will, within seconds the vapor lock is gone, turn the pump off and enjoy the ride.
I do not listen to the high tec people that maintain that the electric pump systems must have a oil pressure switch which prevents the electric pump from working if the engine is not running. At times I have installed a small red light in the wiring to the pump as an alert that the pump is on.
The first summer I had my '36, which was the summer of '53, I installed an electric pump in my '36, summers in eastern Idaho can get into triple digits, the car has had an electric pump in it every since.
When my '39 conv was being built my mechanic installed an electric pump in the fuel line per my instructions.. The pump never worked because of the unnecessary plumbing he installed in the system, pressure switch and a back flow valve, which caused the fuel to return to the tank in lieu of going to the engine.
We recently removed the unnecessary plumbing, installed a new Carter pump and fuel filter, per Carter's instructions, the fuel system now works as it should, a flip of the switch turns the pump on, priming the carb, the engine fires right up.
 
An added thought on poor starting on a hot engine.. I recently had my '39 into the tuneup shop. The engine has a four barrel AFB carb on an Edlebrock manifold.
I made mention to my tuneup man, Bill, that the engine was hard starting when it was warmed up, on very warm days the engine would crank and crank before it would start. I had mentioned this problem to several other mechanics during the five years that the car has been running to no avail.
Bill took one look at the engine and stated "the carb needed an insulator" between the carb and the manifold.. Remember, the majority of engines had a thick brown spacer block under the carb.
Bill sent me to the parts store to get a carp insulator, Edlebrock still sells them, Bill installed the insulator... Wonders be wonders, the engine now fires right up, hot or cold.
 
I have an electric pump in addition to the stock pump. I use it like my old hot rod days; turn it on until the ticking slows, indicating pressure in the system. My 94 carbs sit on an Eddie Meyer "high rise" manifold. The operating temp is usually around 175d. I like blucar's idea even tho the carbs are a distance off the engine. Does anyone sell spacers for the old three bolt pattern carbs?
 
cuzncletus, what type (brand/ and or part # ) electric fuel pump do you have? I used to have one like that, but it quit a couple of years ago. I can not find a replacement 6 volt old style "pulse" type pump where you can hear the clicking, and it slows down as the pump builds press., and fills the carb. I would be interested in knowing what you have , and if that pump is still available. the one I used to have was an A/C Delco EP 11 . ( no longer available ) Thank You---Jim.
 
Heat build up of the engine on a hot day can cause vapor lock with the crappy fuels we have now and especially winter fuel stocks. There may also be an internal fuel leak in the carburetor. If it has an 8BA model 48 Holley then it may have a bad power valve that leaks or a warped casting the renders a gasket ineffective. The clothes pins idea can work on certain applications but it doesn't act as a heat sink. It acts as an insulator for the fuel pipe in the hot areas when you gang them up. Looks funny though. There are much better insulators available that don't look so funky. The bakelite carb spacers help as an insulator and some folks fabricate an aluminum shield that can force the rising heat away from the carb and heat sink it a bit. There are a few good ways to minimize vapor lock a long as you can figure out where the main problem is.
 
The engine in my '36 is a well built 59AB with an Offy Super manifold, Stromberg carbs. I feed the fuel from the mechanical pump to a fuel block on the firewall, the fuel lines then go to each carb.
This setup has been on my car since the spring of 1954..
 

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I saw the spacers at Hershey that are supposed to cure vapor lock. Maybe that is the insulator that blucar was talking about? Any other comments on this "cure?"
 
Had the same problem with my 36 this summer. Ordered a carburetor spacer from Robert Shewman. It is vented & comes with 3 long studs and 2 gaskets for $30.00. Problem solved. His ad is the V8 times.
DK
 
This sounds like my car when I first got it. Same engine 12 volt.
I found that when it was changed to 12 volts the resister under was never removed dropping about 1.5 volts from coil.
Most vapor lock, engine is running to hot.
My 1954 6cylinder has been doing that and waiting for a new radiator to get here.
 
There are many people that have no idea what a ignition ballast resistor is, or what it's purpose is.
As a general rule the '30 model Fords had a ballast resistor mounted in the inside of the cowl above the steering column. I am not sure when the resistor was relocated to the engine side of the firewall.
Shortly after purchasing my '36 in 1952 I started to have trouble with it not wanting to start when it was hot, and/or stalling from a "vapor lock". It turned out to be a bad coil which was being effected by heat, a new coil solved the problem for a while. A bad coil can produce a problem similar to fuel delivery.
Over a period of time I replaced three coils. Talking to a mechanic friend of my fathers, wherein he asked me if I had checked the line voltage and/or ballast resistor.. Say What!.. Gail told me where to look, finding the resistor under the dash I replaced it, ending the coil problem and the engine being hard starting and stalling.
A few years ago I was returning from a late fall trip to Montana and Idaho. The weather was turning cold and a very light snow had started to fall. As I came into Twin Falls I noted a large roadside rest adjacent to the river, I figured it would be a good place to stop, taking my boxer dog "Max" for a walk.
As we were walking around the parking area a '55 Chevy pickup pulled in, the truck had all the normal signs of being under construction.
A young lady exited the cab, she walked around the truck and lifted the hood, looking into the engine compartment. Upon closing the hood she walked towards me, as we got closer the lady asked if there was a phone nearby, I told her there was one in the info building, however, of she needed a phone she was welcome to use my cell phone.
The lady needed a phone because the engine in her truck was cutting out and she was afraid that it would quit during the coming storm.
I asked the lady what the problem was, she told me that the truck was her "baby", however, it was driving her and some of her coworkers crazy. The periodic stalling of the engine was becoming a big problem which her an her friends had been unable to correct.
I suggest we look at the engine, upon opening hood I went WOW, there sat a well built V8 SBC. Looking the installation over I noted an HEI ignition and a stock ballast resistor on the firewall with #16 wire running from the HEI to the resistor.
I told the lady that the resistor was the problem, HEI ignitions need a full 12v where-as she only had about 4.5v. The lady informed me that she was an ASE certified mechanic at a local Chevy dealership, I had noted her uniform and all of the patches on it as she was walking up to me.
I removed the wire from the HEI to the resistor, relocating it to the switch side of the resistor. I then looked the truck over, noting that it had a nice new shinny fuel cap. I removed the cap, looked it over, noting that it was "unvented".. I handed the cap to the lady, explaining the functions of a fuel system and how an unvented cap would create a vacuum which would prevent the flow of fuel.
I picked a soda can out of the trash, cut one end off and placed it over the fuel neck.
I told the lady to take the truck for a spin around the parking lot, she came back with a big grin on her face, a very happy lady. The lady got out of the truck, gave me a big hug and told me that I had made her feel very stupid, with all of here training and experience she was clueless to the problems I had pointed out and fixed with noting more than a pocket knife and my knowledge.
The point of this story is to not over think the problem (s), and don't try to reinvent the wheel.
 
Most of us started with simple systems and learned to understand the basics. A lot of the young folks start out with the latest computer operated systems where you need a scanner to figure out problems but they may not know the basics yet. I have one of those high dollar scanners but it won't help a mechanic at all on the old stuff.
 
blucar said:
...I had pointed out and fixed with noting more than a pocket knife and my knowledge.
The point of this story is to not over think the problem (s), and don't try to reinvent the wheel.
Click to expand...

What a great story! A simple repair with a pocket knife and you look like a hero!
You got to love it.
...Terry
 
blucar said:
As I came into Twin Falls I noted a large roadside rest adjacent to the river, I figured it would be a good place to stop, taking my boxer dog "Max" for a walk.

Anyone smart enough to have a Boxer is smart enough to fix anything!!!
Click to expand...
 
My truck used to die and be hard to start when hot when I first bought it. Long story, short....it was an ignition issue. Well, mainly. I also rebuilt the carb and got my cooling system up to snuff.

I don't have a vapor lock issue since I got my ignition sorted out. Even with 10% ethanol fuel in hot Tucson summers. Starts right up.

Still 6 volts, points, oil bath, heat risers not blocked, stock fuel pump. Cranks for a while if it sits more than a few days but, otherwise fires right up.

I don't know actual engine temps. All I have is stock dash gauge.
 
Use a momentary contact switch (have to hold it in the on position) and you will not need an indictator light to tell you the priming pump was left on.
 
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