1979 Spirit moving to high altitude

This is a very nice car, about 52K original miles. Engine is bone stock, (except for the Big cap Ford style distributor cap/rotor), and runs very well. Carb is rebuilt with a Mikes carb kit.

Will it need re jetting to run well at 6000 feet? Is so, what jets to start with?

Thank you,  gz

General rule of thumb is about 1 jet size smaller for every 2000 feet elevation gain.  At 6000 feet, about 3 jet sizes smaller.   I'd just run it and see what it does, then make changes as necessary.   Some Jeep vehicles had a ground wire on the ECM that got plugged in for high altitude.  Not sure if they did it on cars or not.

Bob

tufcj

Odds are your engine is too lean currently. These engines were tuned on the ragged edge of lean originally anyway, and ethanol gas only makes them more so. It will hit ideal fuel mixture around 3000 feet and be a bit rich at 6000 feet, but not bad. 

If it currently burns light to medium charcoal gray on the spark plugs, it will burn dark gray (but not black) at 6000 feet. That is not rich enough to cause problems or bad mileage. It's actually a really great place to be, because it means you can drive anywhere from 0 to 8000 feet with that jetting and still run acceptably well either way.

I tend to leave the original low altitude jetting alone even though I live at 7000 feet because they are not seriously rich, and I can still drive to lower altitude without needing to take my carburetor apart halfway there. 

You could jet your carburetor down leaner for a more ideal fuel mixture at 6000 feet, but then you can never drive to low altitude again unless you jet back up richer before you go. Running a bit rich at high altitude is not a big deal, but running lean at low altitude is. That is how you scuff pistons and ruin your engine. Believe me, I have done it. 

The first thing you will notice at 6000 feet is that your engine makes significantly less power. It hits you right in the torque. You simply cannot make the same amount of power than you did at sea level when there is less air to make that power with. Even with perfect tuning, you will lose 20% of your engine. That is best case scenario. At least you have the 3.08 axle ratio that was standard on cars built for sale at high altitude to help offset the power loss. Most sea level cars had 2.73. You might actually check your underhood emissions sticker to see if your cars was originally configured for high altitude. 

Your engine will idle poorly when you arrive. It will idle slow, and it will idle rich. The idle mixture will need to be adjusted leaner and the idle speed screw will need to be turned to open the throttle more to return the engine back to a proper idle. 

Some engines gain some power back at high altitude if you advance their timing by 5-7 degrees beyond the factory-recommended sea level setting, but others don't. Try it. Advance it then go for a test drive to see if it makes any more power or not. My 232 never made any more power when I advanced it, so I leave it alone. Keep in mind that advancing your timing at altitude is much the same as jetting the carb leaner: you must reverse it before you ever go back to low altitude or else you can seriously damage your engine.