Carb settings/mods for high altitude for 1938 Special

[Guest SteveAS]

I'm taking my 1938 Special on the Snowball Rally next weekend! It's been running great for me for a few years now, but I've never had it at altitude above 2,500 feet. The rally includes lots of driving at over 6,000 feet and one pass at almost 9,000 feet! I have the Stromberg carb (with unknown settings/mods). Should I plan to change any settings or parts this week? Should I bring any parts in case I have high altitude running problems? Thanks, in advance, for your wisdom, gents!

[carbking]

I am assuming the engine is currently running well.

 

Since you do not know the current calibration of the carburetor; the first step would be to remove the main metering jets, and determine their size. Do NOT pay any attention to the numbers stamped on the jet, as many mechanics resize jets. Use a set of orifice drill to determine the jet size.

 

Once you know your existing calibration, prepare a pair of main metering jets 0.002 inch (2 thousanths of an inch) SMALLER than the current size to use at 5000 feet and above. If you are going to do prolonged driving at 9000 feet, a second set an additional 0.001 smaller would be helpful. For just crossing the pass, I would leave the 0.002 leaner jets in.

 

You may need to readjust the idle mixture screws. It would be a good idea to check their setting and record this setting before heading for the high altitude. Then you can easily bring back your existing calibration.

 

Once you come back down below 5000 feet, it will be VERY important to replace the smaller jets with the standard ones.

 

Thank your lucky stars you have the Stromberg and not the optional marvelous Marvel

 

Jon.

Edited April 24, 2016 by carbking (see edit history)

[LAS VEGAS DAVE]

If I was going I would probably just go with the jets that are already in it. It will run richer at the higher altitude but it shouldn't be a problem if the car is running well at this time. If I was living up there or staying for a couple of weeks I would change the jets but not just to get over the pass. 

[suchan]

I drove my '38 Special extensively through the Sierras, including over 8500'-ish Carson Pass, and it never missed a beat, nor did I sense any loss of power.  I think you're good to go.

[Mark Shaw]

I just adjusted the jets before driving up Pike's Peak. 

 

We made it up past tree line before it vapor locked, so hope for cooler weather while mountain driving...

Edited April 24, 2016 by Mark Shaw (see edit history)

[Guest SteveAS]

Thanks very much for your input, gents! I must say, I'm pleased to read several of you have been able to run with no modifications at high altitude. Based on your feedback, I'm inclined to bring a smaller pair of main metering jets, just in case I need them, but try no adjustments or idle mixture screw adjustments first. Thanks!

[Ben Bruce aka First Born]

Steve, I believe the "potential" problem will be less air due to thinner air, causing a richer condition. Probably should be real sure the air cleaner is clean. I believe unlikely a rich condition will be a problem in such a short time. And the engine will not be hurt in any event.

  Now to pay for all this advice, pictures from the rally are required!

 

  Good luck

  Ben

[Guest SteveAS]

I'm back from the trip and the car ran well enough just by turning in the mixture screws that I didn't need do anything more intrusive, which was nice! Thanks, again, for your thoughts, gents!

 

Here are some pictures. The first two are at the starting point near the Golden Gate Bridge. The third is of me and the car in Volcano, California. The last picture is near the summit of 8,600-foot Carson Pass.

As you might guess, my Buick was (by far) the oldest car on the rally.

 

 

[39BuickEight]

Great photos!  I bet that was a blast!

[suchan]

A sweet car! Your photos brought back memories of our migration with a 38-41, from San Jose to Dayton Nevada, over much of the same route.

Thanks.

[Guest SteveAS]

One more picture posted . . .