VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1933-1936 1935 chev fuel percolation problem still happening

Several years ago a group of us were heading to Dayton, Ohio for a Central Meet on a 95 Deg. day and we were running between 45-50 MPH. We pulled into a rest area for a 'potty stop' and as we were about to leave, my
'35 Std coupe refused to start! A quirt check showed there was spark, so it had to be fuel. The fuel line from the pump
to the carb was so hot you wouldn't keep your hand there very
long! One of the people we were traveling with had some ice cubes in a cooler. I took a couple of ice cubes and with them
wrapped I got a napkin I rubbed them up and down the fuel line the ice cubes were all melted.
The coupe started immediately and I never had a vapor lock problem again!
It was very hot, and we were pushing them a little bit. So,agreeing with a previous poster, vapor lock is most likely to occur in the line between pump and carb, especially since it is routed so
close to thermostat housing

Don't anybody remember taking a spring loaded clothes pin and attaching it to the fuel line ( sometimes more than one). Seriously it sounds more like a clog in tank. Are you sure someone didn't maybe put a foreign object in the tank ie( ping pong ball or ladies pantyhose, knotted. Jay

Some may think this is sematics only, but here goes:

Vapor lock is defined as vapor in the fuel pump. The fuel pump is designed to pump liquid, and while it will pump vapor (gasoline in a gasous state), it does so quite inefficiently.

Vapor CAN develop in the fuel line from the pump to the carburetor, but think about this - if the carburetor is out of fuel then the fuel valve (needle and seat) in the carburetor is open, and (assuming there is fuel in the fuel pump), the fuel pump will pump fuel into the line forcing the vapor out of the line into the carburetor. Since the vapor is lighter than what fuel may be in the carburetor bowl, the vapor will be forced out of the carburetor bowl vent. This is called "hot fuel soak" or simply "hot soak".

What happens with hot soak is the air entering the air intake of the carburetor is saturated with fuel, and additional fuel (or vapor) entering the system through the carburetor just makes the mixture richer, in fact, so rich that it will NOT burn. So basically, there is too much fuel, rather than too little fuel which is the case with vapor lock.

The link below describes a method that generally works starting a car with a hot fuel soak issue:

http://www.thecarburetorshop.com/Troubleshooting.htm#Hardstarthot

The good thing about hot soak is that (assuming the owner in frustration does not run down the battery) hot soak will disappear in an hour or so once the engine has cooled off.

Jon.

Jon gives the best advice. A real KING.
Read all of his suggestions.

Jon,
Hope a bunch of folks copy, read and digest your information. The hot soak problem is very common in downdraft carburetors particularly those with the intake manifold bolted to the exhaust manifold.

Good going buddy.

This is good interesting information especially the part about hot starting. I noted that fuel percolation seems to come about after the engine has been turned off. Like Phil Lipton I have experianced fuel percolation under pretty much the same cicumstances as his.I guess the problem is that you dont know you have it until you hop back in the car, PUT YOUR FOOT ON THE ACCELERATOR and then try to start the car. A couple have mentioned using an electric fuel pump to overcome this problem but unless I am missing the point I cant see how that could help given that Jon says that the fuel is already too rich to burn. In Peters original post I am of the impression he was driving when the car cut out. I have never had a fuel percolation problem while driving down the road but maybe others have.

Dad had that problem. As a boy I saw his quick fix was to put clothes pins one after the other along the fuel line. Seems he added "wood" insulation on it! Ha. Ha. But it did work.

that must have been acting like a heat sink?
not sure how clipping clothes pegs to a fuel line helped hot fuel in the lines, but hey, if it worked for your dad, thats great.
Peter

Yes, my problem started when actually driving the car. It started spluttering and I pulled over, having experienced it before.
It ran OK on tick-over , but when revved, got worse so I turned the car off.
In reading the information from Jon, I did the wrong thing. His advice on restarting is good advice indeed and I guess most of us would have floored the peddle and flooded the best.
Next time I will try the "Jon" method.
Indecently, I removed all the plugs to inspect and all were very black and sooty, indicating an over rich mixture, and that checks out with the " JON" story.
I haven't had time to check the fuel lines for blockage or the tank, but will get around to it very soon, hoping for a cool day in the shed...

Peter

Never heard of the clothes peg idea before. Makes me wonder if you were to lightly wrap some copper mesh around the fuel line between the the pump and carburetor whether it would work like the fins on a radiator and disapate the heat. I guess someone has tried it.

I think it would attract the heat as the heat is coming from an exterior source (the engine) and not inside the fuel line.

There is no "magic" in the clothes pins. Wood is a good insulator. If enough of the clothes pins are placed on the fuel line, they will cover a certain percentage of the line surface area, and thus slightly reduce the heat.

A much better solution (although one gets fewer comments at the car show ;)) is to wrap the line with a high-temperature reflective modern insulation.

An even better solution (if the vehicle is a "driver", not a show car) is to install a three line fuel filter right at the carburetor, and connect the "vapor" line to a new fuel line that runs completely back to dump into the top of the fuel tank.

Take a look at newer vehicles with air conditioning and their vapor return line. The factory engineers solved the issue.

Jon.

Dad did not have those fancy insulation things in those days. They used what they had. Times were simple. It will be intersting to see what "low teck" will do. It gets 124 degrees Farenheit during the Summer here in the South (America). Place the pin squeese together parts away from the fan, so the air flow will remove transfer heat off the pins. They will tend to "float" in the air removing even more heat.

I find that ethanol blend gasoline causes many of these problems. I never had vapor lock or percolation until it was introduced.

The reason the electric fuel pump might help is that it would
raise the pressure slightly; raising the pressure also raises the boiling point, just like with your cooling system. The
problem is that raising fuel pressure too high may cause it to
overload the carb needle and seat and cause the carb to flood!
I think maintain 3 1/2 to 4 1/2 psi of pressure would be within specs to function with flooding!

Hi there,
It takes time to sort out these problems and mine are no different.
I have now removed the petrol tank and had it cleaned, nothing unusual was evident..

The fuel gauge was not working properly so I ordered and installed a new fuel sender 30 ohms device from the filling station.

I blew compressed air through the existing fuel line from the tank to the fuel pump and no evidence of a blockage or obstruction was found.

So later this week I will refit the fuel tank and see what happens. I have made a new fuel line from the mechanical pump to the carburetor without any filter this time. So that is the only thing that has changed. All that remains now is to test drive the car on a hot day ans see if the fuel percolation problem still gives trouble.
I need a new box of straws, all donations gratefully received

Peter

In my estimation nothing was done to prevent heat percolation.

I hope that fixes it. But as you know it is a hobby. Good luck.

Hi guys; What does Peter mean when he said he needs a box of straws. Did I miss something? I'm not real sure but do they have ethenal( nuts, can't spell it) gas in the down under? Thanks Jay

Jay,
I think he has grabbed all the straws out of his last box.

Chipper...maybe that is what is missing in my engine bay, Straws and clothes pegs, must go down to "Supercheap" and see whats on special this week...

Peter

Hi Guys;. Well now I understand about the straws. But I think I would end up with the short one. Thanks for explaining that , Chipper. Thanks Jay

In an effort to help our Aussie Buddy, I have one last thought. When it 'vapor locks', just out of curiosity, try
loosening the fuel line at the carb, place a container under
the line and turn the engine over. If fluid gasoline comes
out, it's not percolating between the pump and carb! Make sure
there is an insulator between the carb and the intake manifold, if not, install one! The other thing no one has mentioned, is a stuck heat riser in the exhaust manifold! It
could be diverting constant heat under the carb, causing it
to overheat and causing the fuel in the carb bowl to percolate. It's a remote possibility, but at this point, I feel it's worth a try!

I think so, too. Look between the engine and manifold. The counter weight is there where it is hard to see. Also see spring attached. You should be able to move it. If not it is stuck. If it is closed you are O.K. but if stuck in the "cold" possition you got to move it.