Topic: low elevation to high elevation carb tuning?

[Yotaoverland]

I did a search and couldn't find any info for my question, so I'm not sure if it's been covered. I have a stock 20r with a weber carb. I live in Dallas, TX but will soon be traveling into Colorado for about a month. While there will I have to tune the carb to compensate for the lack of air at higher elevations?

[:)bestgen4runner]

Are you willing to rejet the carb while you are there?
Not sure what your question is?

[Yotaoverland [OP]]

Are you willing to rejet the carb while you are there?
Not sure what your question is?

Oh, I was thinking that at elevation the truck would not run as well, since it's been at such low elevation. I figured I'd have to turn the air/fuel mixture screw a bit while up there if it started running bad. 

[blackdiamond]

I had a Weber on my 85 and it ran well in Colorado, when I lived there, right out of the box.  I don't have the skills to tune a carb and never needed to do so.  I still had it when I moved to WA and it ran fine here as well.

The best mod you can do for a truck with a carb is to install a hand throttle to give you the ability to turn the idle up a few hundred rpms on the fly.  You'll minimize the times you stall by turning the idle up a bit.  You can also do it manually under the hood (I have done that in Moab before), but the hand throttle is a super cool mod with a standard transmission.

http://www.quadratec.com/products/16192_251.htm

[H8PVMNT]

I'd just be ready to tweak your idle and base timing a bit.  I am only gathering information of the stock aisan 22r carb with the altitude compensator on it but I wouldn't think a short visit would not be worth a re-jet.  That being said I can change the main jet on my aisan in about 15 minutes.

Post your results though please!  I'd love to hear if there was a big difference or not in the way it runs.

[helipilot77]

I was hoping he would chime in here. H8PVMNT has probably spent the most time of any of us learning the ins and outs of the AISIN carbs and he lives at high altitude. In your case I would think that the HAC (High Altitude Compensator) would automatically do its job. Just make sure is still attached and functioning properly.

[H8PVMNT]

I was hoping he would chime in here. H8PVMNT has probably spent the most time of any of us learning the ins and outs of the AISIN carbs and he lives at high altitude. In your case I would think that the HAC (High Altitude Compensator) would automatically do its job. Just make sure is still attached and functioning properly.

I think he has a weber so I don't really know anything.  He would have to be his own HAC.  I need to put a weber on something just to learn about them...

[:)bestgen4runner]

 
First step read the repair order. Understand the complaint.

[helipilot77]

Whoops. Missed that.   

[blackdiamond]

First step read the repair order. Understand the complaint.

Second step, perform a 59 point inspection and suggest 47 additional repairs ranging from topping off blinker fluid to adjusting their power band.

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[Yotaoverland [OP]]

I'm currently in Durango, Colorado. I left Durango a few days ago and was in Moab, then just got back to Durango. At higher altitude, the Toyota runs like complete . 2nd gear 15/20mph up mountain passes and it now has a weird sound as though there's an exhaust leak, kind of a buzzing noise as I'm on the throttle. Oh, and the loss of power is a joke. I don't have any jets to re-jet. So I may mess with the idle a bit. Once I'm back home though, I'm saving up for a 3rz to put in it. The 20r was just recently rebuilt, bored .20. Maybe it's time to retire it..

Also, while going up hills, there's a strong smell of gas. I assume it's running really rich at these altitudes, that won't hurt it, right?

[blackb13se-r]

Thinner air. Means it'll be running richer.  Running too rich can "white" wash the cylinder walls and mess the rings up.

[Yotaoverland [OP]]

Thinner air. Means it'll be running richer.  Running too rich can "white" wash the cylinder walls and mess the rings up.

Would a simple tune of the mixture work? I plan on being on this trip and at altitude for a little while.

[H8PVMNT]

Set your carb per instructions, I think there is a good weber thread here.  Then play with your timing a bit. I would get some jets if you are going to be there a while.

I had a buddy here in Montana that just couldn't get his weber right and you are higher than we are.  He ditched it for a slightly modified 22r carb which handled the altitude way better.

[blackdiamond]

I'm currently in Durango, Colorado. I left Durango a few days ago and was in Moab, then just got back to Durango. At higher altitude, the Toyota runs like complete . 2nd gear 15/20mph up mountain passes and it now has a weird sound as though there's an exhaust leak, kind of a buzzing noise as I'm on the throttle. Oh, and the loss of power is a joke. I don't have any jets to re-jet. So I may mess with the idle a bit. Once I'm back home though, I'm saving up for a 3rz to put in it. The 20r was just recently rebuilt, bored .20. Maybe it's time to retire it..

Also, while going up hills, there's a strong smell of gas. I assume it's running really rich at these altitudes, that won't hurt it, right?

I don't remember having that much of a power loss on the passes in the Durango area, but I did have to drive it like a racecar to keep my momentum.  It's been long enough that I can't remember if I was trying to maintain momentum in 3rd gear or 4th, but knowing that I could run 60+ mph in 3rd I double I was going fast enough to warrant 4th gear.

I do distinctly remember dropping into 2nd gear on the eastbound side of Vail Pass and also the Eisenhower tunnel approach.  Elevation is no joke, significant power loss is to be expected.

Snoqualmie Pass here in Washington is a joke compared to the mountains of Colorado.  In my 85 I could maintain 70+ mph in 4th all the way to the top if I was able to keep it rolling.  The 4Runner is heavy enough that I have to drop into 3rd no matter what for a couple of sections.

My Weber was run exactly like it came out of the box and I lived in Colorado Springs at the time.  If your Weber has been tuned for Texas it's possible that it's a much bigger change going to high elevation.

[Gnarly4X]

Hi colezombie,

I’m a long ways from an expert, but I’m on my 4th Toyota truck and I ran Weber carbs for about 5 years on a VW engine.

You will experience about 4 HP drop for every 1,000 feet climb in elevation from sea level with that engine – so it will feel sluggish and may be a tad hard starting.  Other than running a little rich, it won’t damage the engine. Running rich will most likely degrade the crankcase oil viscosity properties.  After returning to Dallas (elevation 430 feet), I would change the oil and filter.  A good tune (plugs, cap, rotor, etc) will help in Durango (elevation: 6,522 feet) with the drop in HP and throttle response.  Running higher octane gas or fuel additives will probably not be noticeable.

For 1 month, it would seem like a lot of work to change carb jets and try to get that Weber happy. If you really want to play with the carb, here’s an excellent piece on turning Webers for higher elevations

http://www.lcengineering.com/LCTechPages/pdf/Tuning%20Weber%20Carbs%20for%20High%20Altitude.pdf

Please let us know how it runs.

Good luck in Durango.

Gnarls.