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Vapor Lock - Few Ideas

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Oldpappy View Drop Down
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    Posted: 16 Sep. 2020 at 9:32am
See a lot of posts about vapor lock issues, particularly from those running their L134 engines at high altitudes. 

This gets me to thinking of a few things.

Being at high altitude would make vapor lock a more persistent problem so it may just be par for the course, but it can be a problem in the "Flat Lands" too.

My grandfather drove a Chattanooga city bus from 1920 until he retired in 1964. When I was a boy, me and my brother would often spend our summer days riding around on his bus. At the end of his shift as he drove back to the "Car Barn" he would often ask us if we wanted some grapefruit. He always had one in a little ice chest where he carried his lunch. I once said "you must really like grapefruit" and he said he didn't care for it. So I asked him why he always had one in his ice box.

He told me that during the Summer all of the bus drivers carried a grapefruit in a small cooler because the constant stop and go traffic in the Summer made vapor lock a problem. He explained what that was and said when the bus suffered vapor lock they would cut the grapefruit in half and push that onto the fuel pump. The days he offered us a grapefruit were days when he didn't have the problem.

There are other things that can help. 

Larger diameter fuel line routed as far away from heat source as possible is one thing. The old WW2 Jeeps had a fuel filter on the fire wall and the fuel line from there to the pump was bad to vapor lock.

Some sort of heat shield around the fuel line?

I have also read that putting just a bit of diesel fuel in the take will help, but I haven't tried that.

On my Jeep I have a carter fuel filter mounted at the carb and one thing this setup does is it moves the line from pump to carb further away from the exhaust manifold heat.  

I was looking at the heater hose fittings which are plugged on my Jeep and wondering what a few wraps of copper tubing around the fuel pump and connected to the heater hose connections would do?

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TERRY View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TERRY Quote  Post ReplyReply Direct Link To This Post Posted: 16 Sep. 2020 at 10:08am
My"opinion" is that what appears to be vapor lock is difficulty in restarting a L134 after it was shut down hot. Except for MB's with military fuel line routing I have not witnessed L134's stopping while actually already running.
The problem with restarting (IMO) is from hot soaking of the carb while sitting and the resulting flooding of the intake making restart a problem. Clearing the flood with wide open throttle works, as does idling before shut down to cool the engine (manifold) some, or let it idle. Opening the hood also helps. I've noticed that if the L134 is allowed to sit long enough the flooding will evaporate.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Oldpappy Quote  Post ReplyReply Direct Link To This Post Posted: 16 Sep. 2020 at 1:25pm
Terry, 

You are probably right about it, at least most of the time. 

The only time I have actually experienced what I thought of as vapor lock was when I drove a Jeep about 15 miles on a very hot day and stopped at a store to get a cold drink. 

When I came back out the Jeep was very hot and would not start, so remembering my grandfather's story, I went back into the store and bought a chilled bottle of water which I slowly poured over the fuel pump. It started right away after that, so all these years I have thought that was the issue. 

Now I am thinking that even that time could have been the flooding issue you describe. It may have just sat long enough to cook that off while I was fussing around with the bottle of water, but I will never know for sure.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote smfulle Quote  Post ReplyReply Direct Link To This Post Posted: 16 Sep. 2020 at 2:21pm
Originally posted by TERRY TERRY wrote:

My"opinion" is that what appears to be vapor lock is difficulty in restarting a L134 after it was shut down hot. Except for MB's with military fuel line routing I have not witnessed L134's stopping while actually already running.
The problem with restarting (IMO) is from hot soaking of the carb while sitting and the resulting flooding of the intake making restart a problem. Clearing the flood with wide open throttle works, as does idling before shut down to cool the engine (manifold) some, or let it idle. Opening the hood also helps. I've noticed that if the L134 is allowed to sit long enough the flooding will evaporate.

Terry,
What you describe is indeed a problem at time. But.....
i  have witnessed many instances of stumble, stumble, die, vapor locking and experienced it this past summer during trail riding around Ouray this summer. Cold water on the fuel pump cured the issue temporarily until a stretch of downhill let the engine and fuel system cool naturally. 
Stan
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bruce W Quote  Post ReplyReply Direct Link To This Post Posted: 16 Sep. 2020 at 2:50pm
  Another very common problem that gets blamed as vapor lock, and can actually contribute to vapor lock, is air leaks into the suction side of the fuel system, from the tank to and including the fuel bowl on the pump. The bowl is actually on the inlet side of the pump and the fuel is “sucked” through the bowl into the pump chamber. The two most common things that I see that allow air to leak in are hose clamped to un-barbed metal lines and a loose pump bowl or bad gasket. The hose clamped to a metal line is often not air-tight, especially if 5/16” hose is used on 1/4” line. When the clamp is used to squeeze the hose down tight, the hose can bunch up and leave wrinkles that leak. These leaks often don’t leak fuel out, but do leak air in, especially if there is a restriction in the line upstream or in the tank pickup. An indication of air leaking in is air bubbles in the glass bowl. If the bubbles enter the bowl from the fuel inlet near the bottom center of the bowl chamber, they are from air entering upstream, in the line or possibly the “shepherd’s crook” pickup in the tank. If the bubbles enter around the outside of the chamber near the glass, the bowl gasket is leaking. Air mixed with the fuel is not a good thing. It reduces the amount of fuel in the pump and the line to the carb and in the carb and makes it take less heat to boil it. I believe it also lowers the boiling point of the fuel. There will almost always be a bit of trapped air at the top of the bowl. Due to the “upside-down” nature of the bowl, it’s almost impossible to remove that last bit of air, but it hurts nothing. Normally the fuel level in the bowl only needs to remain above the screen inside the bowl. 
  I’ve had very little trouble with vapor lock in my CJ2-A, most of it was at a stop after a hard pull on a hot day, as TERRY described. I’ve learned not to “lug” the engine on a long hard climb (actually I learned that as a kid on the farm), but shift down a gear and let the engine run freely. That creates less heat, the fan has a better chance to dissipate that heat, and the hot radiator air that’s blown across the fuel pump and lines is not as hot. 
  Using a windshield washer reservoir and pump, I’ve built a nozzle that will squirt water on the fuel pump if vapor lock seems to be starting. I’ve never used it since I put it on. 
BW 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote smfulle Quote  Post ReplyReply Direct Link To This Post Posted: 16 Sep. 2020 at 3:36pm
Bruce, 
You've got me thinking a bit. 
This vapor lock is a new phenomena for me so I have tried to think what might have changed to bring this on.
One thing I noticed this summer was that my fuel line had wandered over near the fins on the inside of the fender where it was rubbing a bit. There is actually a little divot in the metal fuel line where it was rubbing.  I could not detect any fuel coming out so I jest bent the line away from the fin and split a rubber fuel line and slipped it over the metal to act as a bumper if whatever forces moved the line over in the first place came back into play.
I wonder if this thin spot in the metal fuel line could actually be letting some air in without leaking any fuel out. My fuel pump has a metal bowl so I can't doe the bubble check. 

Stan
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bruce W Quote  Post ReplyReply Direct Link To This Post Posted: 16 Sep. 2020 at 4:18pm
  I know it seems strange that air can leak in where fuel doesn’t leak out, but it can. I helped a friend at FCT one time install an electric pump because he was convinced it was the only way to fix his problem. His tank-to-pump steel line had three hose splices in it. I tried to explain to him that that could be his problem but he wouldn’t hear of it because it didn’t leak fuel. When we got done plumbing in and wiring the pump near the tank outlet and turned it on, his fuel line became a sprinkler. 
  At rest, the only pressure inside the line is atmospheric, same as on the outside. If the tank is full, there is a small amount of pressure caused by the weight of the fuel, but that’s not much because most of the fuel in the tank is below the pump. If the fuel level is down by more than about an inch in the tank, the pump has to go to work and “pull“ the fuel uphill, then the pressure inside the line is less than atmospheric so air can be pushed in by atmospheric pressure. 
BW 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote smfulle Quote  Post ReplyReply Direct Link To This Post Posted: 16 Sep. 2020 at 4:27pm
Ordered a new fuel line. In the meantime, maybe I'll put a dab of fuel tank repair putty over that spot.
Stan
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Post Options Post Options   Thanks (0) Thanks(0)   Quote squidtone Quote  Post ReplyReply Direct Link To This Post Posted: 16 Sep. 2020 at 7:55pm

These Jeeps have a "dead-head" fuel supply from the pump to the carb which makes them super sensitive to "hot soaking" especially after shutting off the engine when hot. If one is not concerned with originality, get a fuel filter from, say, an early 80's Jeep CJ. On those filters is a return line port. Install the filter as close to the carb as possible, then install a "T" in the fuel line that comes from the tank to the fuel pump inlet, and plumb a line to connect the filter return port to that "T".

The fuel filter return port has an orifice restriction to allow just a little bit of fuel to return to the tank (or in this case, the line from the tank) but it won't bleed off all pressure while running so the carb stays filled.

The constant small flow of fuel from the pump through the filter, and back to the "T" will keep the fuel cooler (even when fuel demand is low from the engine) to keep vapor lock at bay.

In addition, when the engine is shut off hot, there is no more "dead head" line pressure to overcome the carburetor needle and seat...the pressure from heat bleeds off through the orifice and back to the tank.

I did this on my Jeep and it works beautifully.
Dave
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Oldpappy Quote  Post ReplyReply Direct Link To This Post Posted: 17 Sep. 2020 at 9:06am
Dave,

That is a genius level idea, and also an excellent description of what "hot soaking" means.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rick G Quote  Post ReplyReply Direct Link To This Post Posted: 18 Sep. 2020 at 11:27pm
A thought occurred to me that a faulty heat riser could contribute to vapor lock.  If your heat riser doesn’t close or only partially closes, then you have some, most, or all of your very hot exhaust gases directed right on the intake manifold where the fuel leaves the carburetor.  Seems very likely to “vaporize” that fuel before it enters the combustion chamber.  Anyone have this problem?

Like Stan, I experienced this problem this summer (actually the same spot he did, just 2 days prior).  It was at about 12,000 ft elevation after a very prolonged climb up (Imogene Pass).  This is the first time I’ve ever had fuel delivery problems.  A little cold water on the fuel system seemed to help, but interestingly enough, my engine temp was between 195-200 degrees.  I’ve ran a LOT hotter (~240) in the past with NO fuel delivery problems.  It is possible that my carb had some air in-leakage issues (at the throttle body) that contributed to my sputtering and stalling.  Yes, my heat riser does work Wink
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Joe Friday Quote  Post ReplyReply Direct Link To This Post Posted: 18 Sep. 2020 at 11:50pm
I don't recall ever having a vapor lock on the F head that is transplanted in my 49 CJ3A, but today I did notice that the  fairly new OMIX ADA exhaust pipe does not seal properly to the exhaust manifold.

Not only was part of the gasket missing, but there was soot covering the edge of the gasket and the plastic fuel filter near it. I'm not a fan of heat and flames near gas, so part of the prep for the Fall Color tour was going to be  replacing that gasket and moving the fuel line and filter away from the exhaust manifold.

OF COURSE nobody locally had an exhaust pipe gasket, so I bought a 12x24 sheet of metal reinforced high temp Felpro gasket material to make a gasket. So with Mike's hole saw and a sttepped drill bit, I made a new gasket and the lead sealed right up. but since I had a HUGE sheet of gasket material left over, I took a spare 8x12 piece of the gasket material and wrapped it around the fuel lines and filter, and clamped it with hose clamps and a bracket to the fender. We've got a whole week of trails around Nathrop to run this week, so we'll see if that helps shield the heat.
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