Carburetors at high altitude

[Belizean]

Well it's not there now. Maybe a long time ago I tucked it back up in the wire loom. Thanks for clearing that up because that was something I never figured out. Manual barely mentioned with no location. No www. either then

 

[Lumpy Grits]

CK the loom shown in the picture, to see if it is in there.
My search'n says it does lean the carb out(stepper motor?)and advances the timing some. Also read it would up the idle rpm via the sol-vac.
LG

 

[mriplaybass]

To get back on the subject there Bass, just how close is the fuel line to the exhaust pipe? Is it in the oem location? Putting an in tank fuel pump is quite a job and I would suggest that you try simpler routes first. Sounds like you really have done your research on that topic.
Edit: There are heat sinks and or fuel line insulation you could try.

My entire exhaust system is hand made. The fuel line is as far away from the exhaust as I could get it. Both the fuel line and the exhaust are wrapped in insulation. As I said before, I believe at 13,000ft and 70°F, gas can boil around 120°F. Not too hard to get that warm under a CJ. Although the fuel line and exhaust pipe on that side are insulated, the insulation does little to protect against ambient temperature.

 

[Lumpy Grits]

The wrap also acts like a blanket to hold in the heat.
I have had better results by using shields to create a barrier of sorts.
LG

 

[Belizean]

So Bass what are you using as insulation and is it wrapped or tubing the line is slid into?

 

[mriplaybass]

So Bass what are you using as insulation and is it wrapped or tubing the line is slid into?

The fuel line insulation is fuel/brake line insulation which is a sleeve that in some places I had to open up to install then zip tie back together. The exhaust insulation is header wrap.
The fuel line wrap works pretty well since it is continually cooled by the exchange of fuel going from, and back to the tank, but obviously, not perfectly. The header wrap does a good job of keeping the exhaust heat in the pipe until it exits out the back. I can touch the pipe after the engine has been running. Problem is, there is still plenty of heat from the engine that still migrates back under the Jeep. I was not able to get the insulation right at the top of the tank. Just not enough time to drop the tank to do that.

 

[mriplaybass]

As far as the altitude jumper wire goes, as far as I know, this is only on the "newer" CJ's that have a computer. Although it apparently does advance the timing and lean out the fuel mixture, that only contributes to better running at high altitude. If there is no fuel getting to the carburetor due to vapor in the fuel line, no amount of computerization can burn fuel that is not there.
The first time that I experienced a vapor problem around 12,000ft, the first thing that I did was remove the air cleaner, and pump the throttle. No fuel squirting down the carb throat. I did not have any starting fluid or gas can with me, so I disconnected the fuel line at the rubber hose below the clutch bell crank. No fuel. I actually managed to improvise a seal around the gas tank fill tube and blow pressure into the tank. It took about a minute, but eventually gas began to flow into a bottle that I had. I used it to prime the carb, and the engine ran. Although excess heat under the hood will cause the carb to vapor lock, most of the people that I know that experience high altitude vapor problems are loosing fuel pump prime due to vapor in the fuel supply line.

 

[Lumpy Grits]

One of the big reasons for v'lock is the location of the fuel filter right over the exhaust in our 6's. It was also a known source for engine fires.
What was AMC thinking
I moved my fuel filter over the valve cover, and that helped much.
Yes, the altitude jumper wire is only found on the OEM 'puter Jeeps. I don't know if it started when the 'puters were first installed, or not.
LG

 

[mriplaybass]

The only time you'll find in-tank FP's is with FI.
Those in-tank pumps are 'pushers' not 'suckers', like our OEM mechanical pumps are.

LG

It is true that OEM pumps suck the fuel from the tank. This further amplifies the problem in my opinion. As I have calculated, at 13,000ft, atmospheric pressure is only around 2.5PSI, causing the fuel to boil/vaporize at around 120°F. By using a "sucker" pump, such as an OEM or externally mounted electric pump, you are further reducing the pressure inside the fuel line and thereby lowering the vaporization point of the fuel even more.

 

[Lumpy Grits]

That's why going to a 3/8' dia feed line to the mechanical FP on the engine helps.
Electric fuel pumps should be mounted as near the tank as possible as they're 'pushers'.
Bass, in your testing. Did you use 'Summer Blend' or 'Winter Blend' fuel for your tests? It does make a difference.
LG

 

[Belizean]

I would imagine summer blend since it would be tuff around 12,000 ft four wheeling with 5-10 ft. Of snow and winter blend just my thoughts

 

[Torxhead]

It is true that OEM pumps suck the fuel from the tank. This further amplifies the problem in my opinion. As I have calculated, at 13,000ft, atmospheric pressure is only around 2.5PSI, causing the fuel to boil/vaporize at around 120°F. By using a "sucker" pump, such as an OEM or externally mounted electric pump, you are further reducing the pressure inside the fuel line and thereby lowering the vaporization point of the fuel even more.

Along with a fuel return line to keep the fuel recirculating to bring up the cooler fuel from the tank.

 

[Lumpy Grits]

If your fuel system is not a recirculation type, you will never truly get away from vapor lock.

LG

 

[mriplaybass]

That's why going to a 3/8' dia feed line to the mechanical FP on the engine helps.
Electric fuel pumps should be mounted as near the tank as possible as they're 'pushers'.
Bass, in your testing. Did you use 'Summer Blend' or 'Winter Blend' fuel for your tests? It does make a difference.
LG

I am told that the fuel in the Ouray/Silverton area is blended according to season. Obviously, none of us has any control over what the fuel blend in the gas station's tanks. Problems can be exacerbated if you are wheeling in the fall after the fuel blend has changed to the cooler weather blend, then you hit some unseasonably warm weather.

 

[mriplaybass]

If your fuel system is not a recirculation type, you will never truly get away from vapor lock.

LG

I have wheeled with BusaDave in Colorado for the past 4 years, and we have had several discussions on what to do about vapor problems. He told me that he does not run a bypass on his Jeep, and I have never seen him have a vapor problem. I know several others that have done away with the bypass filter while using external electric fuel pumps, and they too, have no problems. I am stumped as to why some Jeeps do just fine with OEM or external electric pumps, and others have vapor problems. But, that is why I started this thread, to put all of our heads together and possibly come up with something that may not have been thought of yet.

 

[mriplaybass]

Along with a fuel return line to keep the fuel recirculating to bring up the cooler fuel from the tank.

Precisely!

 

[mriplaybass]

Advance 5 degrees

With some work you could have free FI.
What I did was buy a running 87 sunburban for $400
Took my time removing the FI in my shop.
Sold what was left of the suburban for $850.

Which engine did the Suburban have? I know we have talked about this option in the past, and it is definitely up for consideration. I might have to give you a call for more details.

 

[Posi]

I don't know of any stock CJ wiring that advances the timing.
Post up if there is such a thing I'm always willing to learn new things.

Posi, my '86 came with what was known as an "Altitude Jumper Wire" when grounded advanced the ignition timing and leaned out the fuel. It was supposed to be used above 4000' msl. I Think Lumpy's '85 did also. Check this:
Altitude Jumper

This is the wire I speak of.
Altitude Jumper

LG

Thanks for the link Torx however, that wire has absolutely nothing to do with timing, or advancing the timing.
The link is also misleading, and missing some very important info.
Before grounding the wire you have to manually advance the timing. I do 5 degrees but technically it should be 7.
Then reset the idle
Then ground the wire.
The above is how you setup CJ's with auto trans

If you have a 6 cyl manual it goes deeper.

Do the above procedure then the idle/decel switch vacuum line must be connected to the carb EGR port "instead" of the spark port.
Basically your removing the idle/decel switch to spark port vacuum line.
Run a new line from the spark port to the EGR-CTO
Then hook a line with a T to the 2 bottom vacuum outlets on the EGR-CTO then run it to the carb EGR port.

Again, the ground wire mentioned in this thread has nothing to do with timing.

 

[Posi]

Which engine did the Suburban have? I know we have talked about this option in the past, and it is definitely up for consideration. I might have to give you a call for more details.

Always welcome your call.
The engine in the suburban was a 350. Some folks run the 350 chip in their 360 and say they run fine. However, there are folks out there that will burn them for $50

 

[Lumpy Grits]

Posi-May I ask your source for info on the no timing advance of the jumper wire.
My Limited GOOGLE search'n found a couple of references that it did. But no hard evidence.
I will look into my FSM and see what/if it has any info.
LG