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Old 07-17-2008, 03:35 PM
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JeeplessJohn JeeplessJohn is offline
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vapor locking

my waggy is having some problems with vapor lock when it gets hot it will stop running and wont get gas i replaced the clutch for the fan and it got better but it still does it.. does anyone know how i would fix it so it wont do it anymore
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Old 07-17-2008, 03:47 PM
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Wrap the fuel lines going in and out of the fuel pump that are close to the engine in a heat barrier wrap. Sometimes aluminum foil is plenty.
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Old 07-17-2008, 03:49 PM
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My 86 doesn't have the problem (knocks on fake wood), but my old 78 did. It would vapor lock when you were in traffic at a slow crawl. I tried changing the routing of the fuel lines, etc. Helped, but didn't stop it.

I put on an electric fuel pump, which keeps circulating fuel through the lines and back to the tank and the problem went away.
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  #4  
Old 07-17-2008, 03:59 PM
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Don S Don S is offline
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..
JeeplessJohn;

... Been There, done that!...

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.
THEORY
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.
… A fuel return line is only a small part of the puzzle in preventing vapor
lock. Be sure to read the sections dealing with Overheating and Airflow 101.

OVER HEATING & AIR FLOW

COOLING SYSTEM QUICK CHECK LIST

FUEL PUMP, ELECTRIC 101

Have a good one while you can still laugh about it.. Don S..
If something I’ve posted on the Internet warps your thinking please ignore it. If you don’t know how to ignore something on the Internet send me an e-mail and I’ll demonstrate!

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  #5  
Old 07-17-2008, 08:55 PM
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jrlane jrlane is offline
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I thought I was having a vapor lock problem also. I changed everything. New Fuel Pump and Filter. New Fan Clutch and Thermostat. Then Electric fuel pump and wraped the fuel line with Heat Tape that they use on Motorcycle Exhaust systems. I still had the problem. Well then I was talking to a guy that worked on dodge Products all his life. He said they were the worst But it is not vapor locking. The Problem is that the sock on the Pickup tube in the tank was colasping. He told me to Blow air into the fuel line off the pump going back to the tank. This would blow the sock off the pickup tube. I did this and Bam fixed my problem. He was a Big Help after I spent all that money. No more problems. Been running good for 2 years now. Hope this helps.
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  #6  
Old 07-18-2008, 06:14 PM
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Quote:
Originally Posted by jrlane
He told me to Blow air into the fuel line off the pump going back to the tank. This would blow the sock off the pickup tube. I did this and Bam fixed my problem. He was a Big Help after I spent all that money. No more problems. Been running good for 2 years now. Hope this helps.

That's a common problem, but blowing it off isn't the best solution..if there's junk in the tank the sockless pickup tube could pick it up. I've bought them new for $5 or $6 and replaced them (easy 1 beer fix). Also a couple other "false" vapor lockers are float level and running too lean.

Steve
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  #7  
Old 07-19-2008, 12:24 PM
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bull4377 bull4377 is offline
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My 91 Grand Wagoneer is currently not driveable due to vaporlock-rediculous I know! Everything is newish:-) It runs so nice and cool no overheating issues at all while running. Then when I shut it off for 15-45 minutes and get back in and fire it up it is majorly heatsoaked and super hot and then vaoprlocks almost immediatley. When I pour gas in the carb it boils on contact. I have to let it cool for a long time then prime and good to go. Needless to say it is parked because I am sick of getting stranded.
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  #8  
Old 07-19-2008, 03:27 PM
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Don S Don S is offline
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Quote:
Originally Posted by bull4377
When I pour gas in the carb it boils on contact. I have to let it cool for a long time then prime and good to go. Needless to say it is parked because I am sick of getting stranded.
..

bull4377;

The spacer block/gaskets are good for preventing boil-over on stock factory carburetors and help with the add-on aluminum carburetors.

Quote:
Originally Posted by Don S
..

… 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.




Check out the other links in the article I posted on this thread for more help.

Have a good one while you can still laugh about it.. Don S..
Why did the U.S Government remove food and fuel from the inflation rate?... It sounds better at 4% … I think some of us know better!…
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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
ACRONYMS & ABBREVIATIONS HERE
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  #9  
Old 07-19-2008, 05:48 PM
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Quote:
Originally Posted by bull4377
My 91 Grand Wagoneer is currently not driveable due to vaporlock-rediculous I know! Everything is newish:-) It runs so nice and cool no overheating issues at all while running. Then when I shut it off for 15-45 minutes and get back in and fire it up it is majorly heatsoaked and super hot and then vaoprlocks almost immediatley. When I pour gas in the carb it boils on contact. I have to let it cool for a long time then prime and good to go. Needless to say it is parked because I am sick of getting stranded.

Guys...really...check your float level. These things produce a LOT of heat under the hood and if your float is low by even a smidgen the gas will boil out of the bowl, creating a lean running condition, which produces even MORE heat in the bowl AND the manifold, which eventually runs the bowl down low enough that there's not enough gas coming in and the low fuel content/high air volume mix is boiled out in the manifold before it can get to the cylinders.

And it can take an hour before that cast iron manifold is cool enough to keep an air and fuel mix in it. AMHIK

Just do it...takes but a minute.

Steve
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Last edited by scantar : 07-19-2008 at 05:50 PM.
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  #10  
Old 07-19-2008, 07:56 PM
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waynestiles waynestiles is offline
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there are several other current threads dealing with engine heat and vapor locking. the two seem related. With my 87 GW so far I've added an E'brock insulator gasket between the new Ecarb and Ealuminum intake manifold. That seemed to help quite a bit. Running with the hood hooked on the safety catch so a bit more outside airflow gets into the upper engine bay helped--if you're willing to risk it.
I've been thinking of relocating/insulating fuel lines but realized that reducing overall engine bay heat would be more helpful and a more logical start. A flush'n refill with proper coolent, new thermostat, and radiator cap along with a new heavy duty fan clutch, all seems to have helped. I added a bottle of "Water-Wetter" (Maybe it's snake oil but it probably can't hurt) We had put a new hi-flow water pump in a month or two back
Past week or twos with temps in the low to mid-90s it would run almost-redzone hot according to the dash gauge and vapor lock under load was common.
After these changes (and temps dropping onto the low 80s) it is barely getting out of the bluezone and seems a WHOLE lot happier--no vaporlocking even after parking it and restarting before the heat-sink effect had cooled off. The ambient temp drop has helped I'm sure but I'm just as sure the small changes helped as well
Tomorrow I'll add a fan shroud--a PO had lost it--and I suspect it will make a big difference--maybe the most important. I may also add a removable extension to the airdam to create a stronger low pressure under the engine bay to help suck hot air down and out
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Last edited by waynestiles : 07-19-2008 at 07:58 PM.
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  #11  
Old 07-19-2008, 10:45 PM
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JeeplessJohn JeeplessJohn is offline
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i heard you can use a close pin but i dont know i saw it on waggy and the guy said it works great but how the hell does it work lol
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  #12  
Old 07-20-2008, 05:28 AM
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Where did you get your high flow water pump?
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  #13  
Old 07-20-2008, 07:36 AM
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waynestiles waynestiles is offline
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RE: Clothes pins: they are an old time fix, basically the wooden spring clip clothes pins clamped to an over heated fuel line served as a heat sink to draw heat from the line. it would work IF it was a localized hotspot. I've heard of "old-timers" running with a bunch of them in the scorching dog-days of summer. I've also heard of aluminum foil or cut up tin can wrappings made with various fins being wired to fuel lines. I imagine they'd work a lot better on the older cars that had a whole lot more air space under their hoods. Our relatively newer rigs have engine bays that are pretty crammed with all sorts of heat generating items (various pumps, alternators etc) in addition to the engines themselves (plus an insulated hood) that really raise the temp of the whole engine bay environment


RE: Hi-flow water pumps:
Several of our regular vendor/supporters sell them, aluminum with actual bearings and better designed passages and impeller blades.

However the shop that installed my engine decided that a new water pump was in order. They picked one up at the local AutoZone store, aluminum, with actual bearings, and better designed passages and impeller blades. go figure!
It appears to be the same item as the name-brand sold by our vendors. They are probably all made in the same factory in china anyway--however others may know better than I on this. If you do a FSJ-site subject search on water pumps you'll find quite a bit of discussion of them over the past few years

To my thinking the aluminum ones are lighter than the originals--thus trimming a few pounds and making the engines work a little easier, as will any other weight reductions. In addition while the AL body will heat up faster it will radiate heat better and cool down a bit faster--reducing heat soak a bit. That also applies to using an aluminum rather than a cast iron intake manifold and other components. This is an added benefit to their thermal efficiency in addition to the improved water flow. Ideally a electric thermostatically controlled fan that would continue to run after shutdown to pull cooler ambient air into the bay would be a help too--depending on the trade off in it's own motor design/power draw.
However there is some argument that having the water flow too fast through the system actually can reduce the amount of heat transferred from the engine to the waste air flow. I'm not sure how much of this is theory and how much is rubber on the hot pavement experience.
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Last edited by waynestiles : 07-20-2008 at 08:00 AM.
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  #14  
Old 07-17-2017, 12:49 PM
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AMC-COMMANDO AMC-COMMANDO is offline
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What is a good recommended electric fuel pump? I am growing tired of my vapor lock issues.
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Old 07-17-2017, 07:31 PM
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Quote:
Originally Posted by AMC-COMMANDO
What is a good recommended electric fuel pump? I am growing tired of my vapor lock issues.

This is a pretty common one used:

https://www.summitracing.com/parts/CRT-P4070/

I mounted mine inside the frame rails just forward of the fuel tank (J-Truck). I'd post pictures but photobucket pulled a fast one on us...

Also make sure the fuel filter return spigot is clocked at the 12 o'clock position. This ensure the filter completely fills before returning fuel back to the tank.
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Old 07-18-2017, 08:02 AM
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AMC-COMMANDO AMC-COMMANDO is offline
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Thanks for the info!
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Old 07-25-2017, 07:17 AM
rocklaurence rocklaurence is offline
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Make sure that your using the filter with the vapor fitting on the top. I then installed a RED Top Holley fuel pump and never had the issue again. It also starts a lot easier.
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Old 07-25-2017, 08:11 AM
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AMC-COMMANDO AMC-COMMANDO is offline
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Thanks! Yes, I am using the filter with the return line and the return line is at the 12'oclock position. I added a phenolic spacer, put my cold air intake back on and rerouted fuel lines. It got better, but still have a VL issue. So I guess an elec fuel pump will be next.
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