How to avoid vaporlock:

I borrow a trick from the EFI cars and run a tee fitting at the carb with a small 1/16" orifice in a return line to the tank. This bypasses some fuel which lowers the temp of the gas in the line, helps keep your pump cool also, whether it is a mech pump or an electric. It drops the max pressure slightly but because of the nature of the orifice it bypasses fuel in relation to the pressure in the line. So when the demand for fuel is high the amount of fuel bypassed is lower.

Note: If you have a higher pressure/volume pump you can increase the orifice size. Just measure your fuel pressure in the supply line and keep it within the limits for your carb. This is also a poor man's fuel pressure regulator. Of course if you want to spend some $$ you can get a bypass type fuel pressure regulator which will do the same thing but in a more regulated hi-tech way.

 

Eric,
I've got some questions about vapor lock:
Fact: Fuel will turn to a vapor at a low pressure and high temperature.
Question: Can I keep enough pressure on a carburated vehicle's fuel line to prevent vapor lock?
Question: Why can't the fuel pump just pump the vapor through the carburator?
Question: Vapor lock is not a normal occurence, or is it? Can insulating the fuel line help?
KingFisher

 

>Fuel will turn to a vapor at a low pressure and high temperature.

Fuel will boil at various temps depending on whether it is "summer" or "winter" gas, grades A thru E. It is vaporized at various temps and storage will evaporate the more volatile parts.

Winter gas E will start to boil somewhere between 105 and 122F.
Summer gas A will start to boil somewhere between 140 and 158F.

What grade you have will be determined by location, altitude, and seasonal temps.

>Question: Can I keep enough pressure on a carburated vehicle's fuel line to prevent vapor lock?

Not according to the tables and charts I am looking at in the SME handbook. Even if you could the fuel would boil as soon as it entered the carb bowl.

>Question: Why can't the fuel pump just pump the vapor through the carburator?

The vapor is at a higher pressure than the pump can produce. Usually the vapor bubbles are mixed with the fuel and disturb the carb metering. This kills the engine leading to a complete boiling condition that vaporizes all the fuel in the carburetor and near the engine. Often times this "floods" the engine with fuel vapors which cause other problems.

>Question: Vapor lock is not a normal occurence, or is it?

Normal, No. Common, Yes.

>Can insulating the fuel line help?

Yes! Reflective pipe insulation helps, but any fuel leaks will eat the foam types up. Some people used to wrap the fuel line in aluminum foil.



I just like to use that nice big heat radiator under the truck and circulate cool(er) fuel.

p.s. The numbers above come from some old books and may be changed nowadays. They don't even mention gasohol. Gasoline is a complex mix that is hard to characterize.

 

Thats definetly true. Ethanol doesn't really boil, it gels. I saw it once when we were touring a refinery for my geology class.

I have some flexible metal conduit that is going to fit over the fuel line, that should solve any problems I have.

 

The flex conduit will help just like aluminum foil.

Another thing that helps is a plastic insulating spacer between the manifold and carb. If you are running a dual plane get a 4-hole or divided spacer.

 

Today i was looking under the aircleaner and noticed that it has been gathering a lott of crap over the years. It is covered with dirt and leaves from a gasoline leak from a seal leak in a holley 500 carb. I hate aftermarket stuff so now its all original and Its jsut plain dirty. I don't like that either so I gotta clean it. oh well.