VAPOR LOCK update 04.17.06 You can fix it !
Vapor locks defiantly
CAN happen even using an electric fuel pump !!
This theory is for older "normally aspirated vehicles" but some newer systems are having problems.
Vapor locking will feel like the vehicle is running out of gas and as the temperature rises the engine will quit running. A lot of the time vapor lock happens after a very warm engine is turned off and has set a few minutes. A quick short-term fix is to pour water on the hot fuel lines, pump or carburetor then carefully prime (an electric fuel pump will do this) the carburetor. Overheated coolant can only aggravate a vapor locking condition. Airflow as discussed in the overheating article is also a prime factor in causing vapor lock. Dual exhaust systems often add extra heat to the fuel lines and tank.
Note !! In some cases a Vapor lock can occur when the carburetor is hot enough to boil the fuel. ‘Modern’ carburetors need outside fresh air ducted to the intake or air cleaner for added cooling. Check the exhaust heat riser valve and / or install (some are made of wood) a carburetor flange insulator.
NOTE. Gasoline will boil (vaporize) at some where between 130f and 430f degrees at sea level.
A low carburetor float level can aggravate a vapor lock condition. IF the fuel is bubbling (as seen in a clear fuel filter) when the entire system is cold there may be a small leak in the fuel line (could be inside the tank). If the system is warm it might be normal vaporization for that particular brand/type of gasoline.
As gasoline warms up it vaporizes more readily. All "Brands" or grades do NOT vaporize at the same rate. As pressure is reduced the gasoline vaporizes more readily. Higher altitude is lower pressure. Fuel pumps reduce pressure in fuel lines from the fuel tank in order to draw gasoline. The gasoline can sometimes vaporize faster than the pump can be fed the liquid gasoline. Most fuel pumps have problems pumping vapor.
The gasoline is then pumped (Pressurized) and sent in the line to the carburetor where it could possibly be heated even more. Some systems use a small return fuel line to help control vapor and fuel pressure. The line returns some of the gasoline and vapor to the fuel tank so it will not absorb too much heat while waiting to be used by the carburetor. After driving a few hours in warm weather the fuel in the tank will be gaining temperature, especially with a heavy load and perhaps duel exhaust pipes. Most of the time once a system begins to Vapor lock it seems to deteriorate at a rapid rate as if the pump diaphragm has been weakened. Inspect fuel lines for "pinched" areas.
Basically, shielding, insulating or rerouting fuel lines, and shielding the tank from hot spots. Just insulating fuel lines seems to help a little. One heavy-duty Gyrator style electric fuel pump (such as the Holley redtop at over $100) mounted low and close to the fuel tank with a filter between seems to be the best remedy. Fuel pressure regulators are not often required but helpful. Doing away with the mechanical pump will allow you to route the fuel lines to cooler areas. Running larger size fuel lines (3/8th"metal) outside of the frame works very well but it is NOT safe as far as side impacts (crashes) are concerned. Vibrations in the fuel line may be a contributing factor to vapor lock.
Installing a fuel pump in the fuel tank is like a two edged sword! It keeps all of the feed line under pressure to reduce vapor lock problems but the electric motor can add a lot of heat to the fuel. Replacement on the trail will be more difficult. The electric motor and/or impeller can be damaged when operated in low fuel and when running out of fuel. The damage is caused by lack of coolant (gasoline) and what little lubricant the gasoline provides. Adding extra heat in the fuel tank will add to the vaporization of the gasoline and that will be vented (and lost) to the atmosphere one way or another. Modern vehicles with pumps in the tank have warnings not to run low on fuel.
Gyrator pumps will be damaged if run without fuel to cool and lubricate the steel parts. It is a good idea to bench run a gyrator pump with some light oil for a short break-in. In spite of many claims extra fuel pumps in line do create more friction in the fuel lines so that at critical times all must be running at the same time. Simply adding an electric pump in line with a mechanical pump is doable but will slightly impede the fuel flow unless the electric-pump is switched on. The electric pump may put a strain on the diaphragm of the mechanical pump. If the diaphragm wears out a hole will develop which could cause a catastrophic amount of fuel to end up in the crankcase quickly.
A fuel pump for a six-cylinder engine should put out 4 to 5 psi and a fuel pump for an eight-cylinder engine should put out 5 to 6.5 psi. Both six and eight cylinder fuel pumps should pump one pint in 30 seconds at idle RPM. These are ‘specs’ for all six and eight cylinder 1981 Jeeps per AMC.
It is a good idea to mount a spare electric fuel pump close to the one your are using. Should a pump fail the hoses could be switched quickly.
… Phenoloic spacer blocks up to one inch high were used to insulate the carburetor from over heating and boiling the fuel away. These may be available from Ford or some parts houses. Phenoloic blocks or sheet have been sold at various plastic supply houses and can be cut with a saw and drilled in a drill press to fit. Remember some carburetor insulators are made of plywood.
In this article it has been assumed the fuel systems have been checked for good fuel and fuel flow. A low carburetor float will simulate and /or add to a vapor lock problem. A contaminated "sock" and/or filter in the tank or line and look for "pinched lines or air leaks. Another over looked item is PROPER atmospheric venting i.e., It is possible to create a negative pressure (vacuum) in the fuel system which in turn can lead to fuel starvation and vaporization. Many older vehicles have had their gas caps replaced with the wrong type. Most fuel caps on older FSJs use a relief valve calibrated to open only when a pressure of .75 to 1.5 psi or a vacuum of 1.1 to 1.8 inches within the tank. As a point of safety a dash mounted on-of switch and a rollover shutoff switch need to be installed for the electric fuel pump.
Note! FSJ's with the long (front to rear) fuel tanks will leak fuel from plain vented caps while climbing steep angles.
FUEL RETURN LINES
On PAGE 1J-1 and 1J-9 of the 1981 Jeep TSM; "All (Jeep) vehicles
with six and eight cylinder engines have a fuel return system that
requires an extra nipple on the fuel filter to route fuel back to the fuel
tank. The filter must be installed with the return nipple upward".
‘Some’ Jeeps also had a check-valve in the return line.
The fuel return line can help the fuel pump by removing vapor and
Engine heated gasoline from the pressure side of the pump. In some
cases the return line can reduce pressure spikes from the fuel pump.
Improper placement of the return line will eventually cause the fuel in
the tank to get very hot adding to the vapor lock problem. In a few cases
(by trial and error) the amount of fuel returned may need to be regulated
depending on the output, in gallons per minute of the fuel pump. The
line can be partially ‘pinched off’ with a small clamp or vise-grip.
… When using two or more fuel tanks hooking up the return line to the
tank you use the most… call it tank (A) would be the easiest. When you
are running on the other tank (B or C) some of the fuel is going to flow
into tank (A)… use a three nipple filter up close to the carburetor and the
little nipple up, facing the carburetor and hooked to the return line. Run
the return line in a safe place and away from high heat sources such as
the exhaust system.
Have a good one while you can still laugh about it.. Don S..
Obama said at a news conference Apr/02/09 he was going to give millions to help Africa recover. Question: Why are we borrowing money from China (and paying interest) to give to Africa? Let Africans borrow their own **** money!
Sold our 1976 Wagoneer 406, MC4300, TH400, QT, TruTrac, 2" lift, 31x10.50s, duel Optimas,
It’s took us over 161 Colorado Mountain Passes, 3 Jeep Jamboree USAs & 2 Ouray Invasions from 1985 to 2010
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