High Altitude 1977 Spider (in Cali)

[Texafornian]

After an intense weekend replacing the timing belt, tensioner, water pump, and radiator and some vacuum and fuel hoses, I'm about ready to brave the smog police in Cali. I knew my Spider came from Colorado originally, but as I was crawling all over the engine bay I noticed that on the sticker in front of the radiator there was a notation that it was "intended for sale at high altitude." Question for you knowledgeable folks - what does this mean in terms of specs? Different jets in the carb? Other mods? I know that it passed Cali smog about 7 years ago when it was first brought into the state, so am less worried about that, more worried about getting the most out of it at low altitude. Is there anything I should be concerned with adapting?

[johndemar]

I would question whether it makes any kind of significant difference. The car I have spends the winter in Phoenix (approx 1,000 feet above sea level), and summers near Flagstaff, almost 7,000 feet. Seat of the pants, I don't notice a difference, although I'm sure jetting and air/fuel mix can be adjusted.

[Texafornian]

Thanks John, I tend to agree, but am still curious if anyone knows what constitutes a "high altitude spec" Spider...

[PhillySpider]

Air is lower density at higher altitude. You're getting less oxygen, argon hydrogen etc in the combustion chamber at altitude and lower compression. Rule of thumb is a 3% power loss per 1,000 feet of altitude. Basically a 100hp engine at 5,000 feet will perform around 85hp. YMMV .

[WeberCarburetorGuys]

ANY carburetor when properly jetted for elevation will have smaller idle jet(s), and bigger air jet(s), compared to the same carburetor jetted properly for sea level. Main jets may differ also.

To answer the OP's question, we recommend changes every 2500' of elevation change. This is OUR recommendation, not Fiat's nor Weber's. The difference is significant. From 1k' to 7k', is "to us", 2.5 jet changes apart. That is huge! Even sea level to 4k' is a lot.

Understand that at elevation (lower pressure) there is "less air in the air", so the same amount of fuel will require less air. Or looking at it the other way, the same volume of air will require less fuel (leaner jetting).

While you can take a car jetted for lower elevation, and safely drive it at higher elevation, it will run richer than at sea level, since there isn't as much oxygen available. This can foul plugs, and certainly drop MPG, as unburned HC's flow out the tailpipe. However, if you take a car properly jetted for higher elevation, and drive it at lower elevation, it will run LEANER. This can cause problems from the lean operation, and can break parts.

Basically it's fine to take a car jetted for low elevation and take a trip to a high elevation, it doesn't hurt anything. Just don't do the other way! Any engine is going to lose power at elevation, since there is simply less O2 available. But if the engine is also running "richer" due to lower elevation jetting, the power loss is worse than if the jetting is corrected. The jet change minimizes the power loss from elevation.

If you are going to drive for more than 6-8 hours "at elevation" it's not a bad idea to re-jet. It is not that difficult once you learn how, and it puts you that much more "in tune" (pun intended) with your ride! Just keep the proper jet(s) in the glove box or tool box, and you usually only need a screwdriver to do it, once you know what the proper change(s) are.

[Texafornian]

Thanks for the details. I think that is what I was looking for. By "break parts" what would be the potential trouble spots? I guess I'll be learning a lot more about carburetor jets here soon...also, any hacks to get as rich as I can in the meantime (turn mixture screw in)?

[So Cal Mark]

turning the mixture screw in will lean the mixture, not richen it. The high altitude condition will help the car pass Calif smog test since the CO limits are so tight now

[WeberCarburetorGuys]

"running lean" is a mis-understood term. Actually running 16-17:1 runs very cool, cooler than 13:1.

What brings concern is when you are in the "death zone" of 14-15.5:1 (stoic is 14.7:1). This is the area where it will run hottest, and the combustion burn is fastest. It will fully test your exhaust valves, gaskets, ignition timing (pinging), etc. If you have a leaky valve, the stoic tune will finish the job!

Most operators of vintage cars will aim for 12.8-13.5:1 for the best balance of cool running, power, and smoothness. This ratio is the same for sea level and elevation. "Lean cruise" tuning is a more advanced ballgame, and more challenging, but fun and worthwhile IMO.

[BwBrown]

Having lived in Colorado Springs, I never experienced any real "high altitude" problems 'til I got up around 10,000 feet. Then the engine would start to run rich. Since I lived at 7,000 feet, I just "ear tuned" the carb there and it would survive all the ups and downs without problems.
All the previous details are spot on.
Good luck,
Bob;

[Texafornian]

I wanted to close the loop having been through a carburetor rebuild this weekend. According to Mr. Artigue, this is the default jetting for a 77 ADFA (along with my setup):

Main Jet - 1.25 Main, 1.40 Secondary (1.20 Main, 1.35 Secondary)
Idle Jet - 0.50 Main, 0.60 Secondary (0.50 Main, 0.60 Secondary - no difference)
Emulsion Tube - F73 Main, F7 Secondary (F73 Main, F7 Secondary - no difference)
Air Corrector - 1.85 Main, 1.70 Secondary (1.90 Main, 1.70 Secondary)

Have some new jets on order, we'll see how it goes. For those of you who know carbs, what should I expect from the change based on what I have been running?

[Nanonevol]

What change are you planning to make? If your going with Brad's suggestions, you're pretty close as you know. My '77 with a 34ADF would stumble accelerating with a 120 main primary jet but runs great with a 140. The accelerator pump is another variable you can look at.

[Texafornian]

I had to do a carburetor rebuild anyway to address a fuel leak, so taking the opportunity, I'm planning to go with Brad's as a way to baseline (e.g get to "stock") and I will go from there as I learn. Having fun and learning a lot!