Vapor lock

C

carolinamudwalker

Member
What exactly causes vapor lock? And how can changing to another up-draft carb be a cure? Is it the engine itself running to hot in the summer? Or is it the carb sucking in hot air from the exhaust manifold? I have read the service bulletins cover to cover and there is no mention of there being a problem back in the day so what gives? Bob
 
Ohh, I'm so grabbing a bag of popcorn while I sit back and watch this one unfold!!

Bob, this has been debated several times in the past here. Folks say that it is because of cheap fuel & the underhood temps however they cannot explain why the same phenomenon does not happen to all of the riding mowers out there! ;) My personal opinion is folks will only believe what seems believable to themselves!! :D
 
Last edited:
Vapor lock- What to call a problem when you do not know the solution.

The true vapor lock is a condition on cars with pumps where too big a bubble appears in a fuel line and the volume of each push of the fuel pump can not push through the bubble. We had this problem in our 39 Ford. The fuel pump was marginal and the heat of a parade would get to it. We knew the problem because there was no gas in the carb. A rebuilt fuel pump fixed the problem.

For example, One person told me about how he believed in vapor lock cause his car kept stopping when it was hot out. He tried everything to fix vapor lock and it did not get fixed.
The engine had to come apart for other reasons and he found some of the valves were marginal with their clearances.
He put the engine back together properly and the engine no longer would stop for no reason. It just kept running.

More often the problem is electrical. A borderline coil, a flaky wire, or a condenser that is not happy.

You have to imagine what might happen. A few valves with the gap set wrong, a worn cam that has some variation of the lobes, a block with some rust scale, a carb not set right and so on. Each engine is going to have a point which takes it over a line.

So the problem can be subtle and the result of several things each seeming to be in spec. Under the right conditions they rear their ugly head.

The thing to understand is the engine does not normally have a problem. If you have vapor lock do not buy into the standard treatments. The problem is you may have to dig very deep to find the issue.
 
There's definitely a problem when you unscrew the gas line at the carb and only gas steam come through for the first few seconds.
 
It is a real problem that can happen on hot days.

Sadly, the so called experts on the forum do not trust that people can have this problem because "they" say it can't happen.

I have had vapor lock occur on hot (100 degrees) days in Colorado after a good high speed run down the "diagonal" (Longmont to Boulder road).

After stopping at a traffic light, my Model A ran rough and I needed to pull out the choke to keep it running. After a brief trip after the light, the car ran fine. Only happened with straight 10 % ethanol gas and only when the temp was around 100.

Marc
 
Exactly what Marc said, except I've had it happen on 80* days when using the crap gas. I've never had a problem as long as I use the good gas without corn crap in it.

I've also experienced what Gold Digger said, and it happened twice in one afternoon when the temp was about 80* and I was parked for a couple hours. The engine wouldn't start because the crap gas had boiled away in the carb, and I couldn't restore flow until I disconnected the fuel line at the carb. As soon as the crapahol started flowing I reconnected the line and drove home.

My 1952 Studebaker Land Cruiser has the fuel pump mounted up high on the V8 engine, and this should really lead to vapor lock, but that car never gave a problem because we had better (real) gas in the 60's and 70's. This is the main reason for putting the electric fuel pumps inside the gas tank these days. It keeps the entire fuel line under pressure, so you don't have vapor forming in the line.
 
marc hildebrant said:
It is a real problem that can happen on hot days.

Sadly, the so called experts on the forum do not trust that people can have this problem because "they" say it can't happen.

I have had vapor lock occur on hot (100 degrees) days in Colorado after a good high speed run down the "diagonal" (Longmont to Boulder road).

After stopping at a traffic light, my Model A ran rough and I needed to pull out the choke to keep it running. After a brief trip after the light, the car ran fine. Only happened with straight 10 % ethanol gas and only when the temp was around 100.

Marc
Click to expand...
More on that. And yeh I knew the diagonal since it was a toll road. Vapor lock was common back in the 40's and 50's. It was no ethanol then and altitude had something to do with it. So, if your car had the problem in the summer and at high altitude you wrapped the gas line loosely with tin foil and held it on with clothed pins. Remember the canvas water bag? Cool water was poured on the fuel lines and the carburetor. I don't know the science but it did work.
 
I will be running a complete description of the cause and what to do about it in the Times in the Summer issue. Basically it is the boiling (vaporizing) of the fuel before the carburetor.
 
Two of the experts have spoken ( Brent and Tom ) with opposite opinions! So no matter what, this subject will never reach a conclusive answer! Wayne
 
Great question but I hate to say this guys...but in all my 35 plus years driving Model A Fords (winter, summer, spring or fall)...I have never experienced "Vapor Lock". Hmmmmm...Better "Knock On Wood" with that one.

So tell us Mr. One Star...why is this not an important question to you?

Interesting.

Pluck
 
When the "vapors" hit we would use the cloths pins and/or would wrap HD aluminum foil around the fuel lines.
On the way to delivery our clubs toys to the Salvation Army this Christmas it happened to my A. plus overheating for the first time. I never use the corn EPA fuel.

Richard in New Bern
 
In my newbie opinion if corn base fuel sits in a hot carburetor (after a drive) the fuel may turn to vapor more easier than 100 gasoline. I think though with cool fuel from the cowl tank flowing in the the bowl that's not likely to happen... But once you turn the car off and let it sit... you might in theory experience this... Tests and experiments could likely proves this once and for all... I might take a carburetor with a small port-hole on the side of the bowl and a camera to really prove or disprove...
 
A short version, altitude, temperature and fuel make up all create the problem. The last trip over the Continental divide on the 2012 Summer Tour 24 of the 25 Model As suffered the vapor lock condition.
 
JohnLaVoy said:
A short version, altitude, temperature and fuel make up all create the problem. The last trip over the Continental divide on the 2012 Summer Tour 24 of the 25 Model As suffered the vapor lock condition.
Click to expand...

But is the root problem because of the fuel, ....or a mechanical issue that is the cause? (i.e.: "My Model-A always runs hot ...but I don't use a cooling fan." or "Model-A lights are too dim on 6 volts so I replaced my dingy original reflectors with sealed beams.")
 
Apple slices go good with popcorn Brent! AER in his instructions on operating his engines
says to not close GAV past 1/2 open, because of the nitrogen enriched fuels today!
This extra flow would help with vapor lock? Is the nitrogen enriched fuel the same as
corn gas or is it a double wamy?
 
You must log in or register to reply here.
Back
Top