Carburetors at high altitude

[mriplaybass]

As many of you know, a few of us have had some vapor problems when operating carburated engines when at high altitude on the Ouray Colorado trips. A discussion started on my trail report about this, but I think that it might be a topic that others would like to discuss, and might not find in a trip thread. So, rather than hijack my own thread, here it is folks!

I know that those of us who have converted to EFI, have had little to no problems operating over 10,000ft. I have done much research on high altitude fuel mixes and fuel delivery systems, but I would like to hear more from those who have had fuel problems at high altitude in the past, but have solved, or at least have some ideas on how to run a carburetor up in the mountains.
Obviously, EFI is the one of, if not the best way, but for many of us, the cost is prohibitive.

 

[Belizean]

Great subject to discuss Bass. I have never driven high altitude but have driven steep trails and have had problems with stalling on steep inclines. That is the main reason I will hold off going to Colorado until I get FI installed. My vehicle performs going up, but the stopping midway is when the problems begin so I'm sure I would be in problems there

 

[Lumpy Grits]

I learned to run the highest octane fuel you could find, helped a good deal.
The high altitude GND wire on my '7' sure helps above 6K' ASL.
I have had my OEM, carb'b '7' above 10K' ASL with little issue on a few cool days. Power loss was noted.
I usually do have to up the idle some.
Here's my question-What do folks do with their ign timing at the altitudes you folks saw on the trip?
LG

 

[Lumpy Grits]

Great subject to discuss Bass. I have never driven high altitude but have driven steep trails and have had problems with stalling on steep inclines. That is the main reason I will hold off going to Colorado until I get FI installed. My vehicle performs going up, but the stopping midway is when the problems begin so I'm sure I would be in problems there

Have you confirmed the float setting is correct?
Also look at a fuel pressure regulator and set to no more than 3psi.
LG

 

[Posi]

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.

 

[Belizean]

LG checked float level a long time ago but no telling what it is now. I know it is a rich mixture problem at that point. Posi I have a Webber on there and they ( Webber) recommend it be set pretty advanced already. Off hand I can't remember what that is. I live in flat land country here and haven't needed to deal with that in some time. Once I get to and finished my new to me rebuilt engine I hope to leave this problem behind along with the carb with FI. Thanks for the ideas, who knows I may have to resort to them if I do go on a mountainous vacation in the future. Cheers

 

[mriplaybass]

Great subject to discuss Bass. I have never driven high altitude but have driven steep trails and have had problems with stalling on steep inclines. That is the main reason I will hold off going to Colorado until I get FI installed. My vehicle performs going up, but the stopping midway is when the problems begin so I'm sure I would be in problems there

Does your engine flood, or starve in this situation?

Have you confirmed the float setting is correct?
Also look at a fuel pressure regulator and set to no more than 3psi.
LG

Agreed, if the float setting is off, flooding or starving will occur when on extreme angles up or down

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.

Exactly where I set mine. I actually installed a pointer and put marks on the distributor cap in order to do quick field adjustments.
I have considered the junk yard EFI. Than is definitely something that is on the table.

 

[mriplaybass]

I have done a lot of research on what happens to gasoline at high altitude vs ambient temperature vs fuel additives.
Here are a few of the things that I have hypothesized.
According to my calculations, here in Wisconsin where I live, the atmospheric pressure is around 13.07psi. @70°F. At the same ambient temperature, the pressure at 10,000ft drops to 3.96psi, and at 13,000ft, it drops to 2.50.
Anyone who has used a pressure cooker knows that as you increase the pressure inside the cooker, the boiling point of the water is raised. I also know from experience in testing construction aggregates under a vacuum, as the pressure is reduced, the boiling point of the water is decreased.
From what I have read, gasoline behaves the same way. As the atmospheric drops, so does the boiling point of the gasoline. I know that there are additives put into the fuel to compensate for temperature differences at various times of the year, but in this day and age, they are doing it pretty much assuming that all vehicles are EFI, and have computers to make constant adjustments, not to mention, the fuel pumps are in the tank.
If I remember correctly, it is possible for gasoline to boil at as little as 120°F at 13,000ft on a warm day, and we all know that there is plenty of heat from exhaust pipes to get the undersides of our Jeeps that warm.
My theory is, if the fuel pump is located inside the fuel tank, not only is the pump kept cool, but the entire fuel system from the pump to the carburetor is under pressure thereby raising the boiling point of the gas well above the under Jeep temps.
I have never had vapor problems at the carburetor itself. It has always been in the fuel line. I think we would all agree that whether we are using an electric fuel pump, or an OEM mechanical pump, they are all designed to pump liquid, not vapor. Hence, my theory.

 

[Belizean]

Engine floods and mixture is rich. Got a buddy who is master mechanic and has had a lot of jeeps his who life from WW ll surplus to 80-90s jeeps. He has said many times never let fuel pumps in tank run below 1/4 tank because fuel pumps over heat and burn up. Have a 96 Cherokee with MPI

 

[Lumpy Grits]

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.

Here in the land of the NOT so free(CA),we can only use state approved FI set-ups. No junk-yard deals, even if they meet the tail pipe specs
For now-I'll stick with my OEM carb setup. I do pass the smog tests, which I'm sure pisses the state off to no end()
My engine is 32+ years old, with 121K+ miles on it. Still runs strong and I show good oil psi at freeway and idle.
Have had a bit of lifter noise that a can of Restore took care of.
Was raised on carbs, and to me that's what I 'speak'. Can and have serviced them in the field, when it was necessary to do so.

Have had my '7' many times between 8-10K' ASL with little issue. Just wondering what special stuff the carb guys did for the Co. run when 12K+' is common.
I'll have to confirm this-But I believe part of the high-altitude settings that wire on my Jeep draws into play, does advance the timing.
LG

 

[Belizean]

LG that thing is just barely broke in and you need a can of restore ? . Mine is 33 years old with over 235 K and runs smooth strong and no smoke ever. Only thing I wish mine had was 2 more pistons

 

[Lumpy Grits]

I run her hard in the dunes with many red-line shifts.
LG

 

[Torxhead]

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.

 

[Lumpy Grits]

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.
One other thing-Under hood venting of engine heat needs to be addressed to reduce vapor-lock.
I have 2 hood vents on top of the hood, that are centered back near the rear of the hood.
When my electric 'pusher' fan comes on(mounted inside of grill before radiator). I am always surprised with the amount of heat being pushed out via these 2 vents.
LG

 

[Posi]

Yeah, sometimes it must suck to live in CA
I think every state has a little suck in it.
32 years old? That's one of those newer Jeeps.
Last year on the CO trail ride my completely stock 48 year old carbed CJ ran without any fuel issues.
It was set up from the factory, advanced 5 degrees with the proper size jets.
When the shipper dropped it off at my place 100ft sea level it ran like .
Simply retarted the timing 5 degrees and adjusted the fuel and air and it ran perfect.
So, anyone going from sea level to 13,000ft would need to advance the timing 5 degrees as I previously mentioned and possibly change the jet size.
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.

 

[Belizean]

 

[Torxhead]

Yeah, sometimes it must suck to live in CA
I think every state has a little suck in it.
32 years old? That's one of those newer Jeeps.
Last year on the CO trail ride my completely stock 48 year old carbed CJ ran without any fuel issues.
It was set up from the factory, advanced 5 degrees with the proper size jets.
When the shipper dropped it off at my place 100ft sea level it ran like .
Simply retarted the timing 5 degrees and adjusted the fuel and air and it ran perfect.
So, anyone going from sea level to 13,000ft would need to advance the timing 5 degrees as I previously mentioned and possibly change the jet size.
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

 

[Lumpy Grits]

This is the wire I speak of.
Altitude Jumper

I live at 2700' ASL and have the wire on a toggle switch on the dash, for when I head to the mountains.
LG

 

[Belizean]

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.
Altitude Jumper

Torx mine came with that Altitude Jumper also but I never figured out where it was. Of course the YFA Carb is gone now but I'm still curious where it is located

 

[Lumpy Grits]

It's a fairly large ring terminal.
Look at the lower arrow in the picture from my link.
I just attached it to the coil bracket, before going to a toggle switch setup.