Altitude Adjustment

[Jetaway]

Hi, all.

1972 240Z, electric fuel pump, 280ZX Dizzy, otherwise dead stock on the "go" side. My little town sits about 30 feet above sea level. In a couple of weeks I plan on heading up into the Sierras for a driving around vacation. I suspect I won't be below 3000 feet most of the trip and will quite likely get up well over a mile above sea level. I seem to remember from back in the pre fuel-injection days that high altitude adjustments were necessary, or at least desirable for performance and drivability. Just using the mixture knob, what sort of adjustments should I make? A ballpark suggestion is all I'm looking for, I'm not so OCD as to retune for every 1000 foot change in elevation.

Chris

[Zforce]

You could lean it out a touch, when I fly I I start leaning above 3000 feet. There is no ballpark suggestion, too may variables, temperature, hummidity. What you are trying to maintain is a 15 to 1 air/fuel ratio. When you get up there you might notice the engine idling a little low,dont change the idle speed just lean it out some and the idle will pick up on its own. Be sure and richen it back up when you come down.Fyi you lose about one inch of mercury per 1000 feet of altitude and lose about 2.5 degees of temperature per 1000 feet lapse rate.

[Gary in NJ]

If your carbs are properly balanced and working well, I'd leave it right where it is. You car will run rich in the higher elevations, but it's just not worth the effort of adjusting/sync'ing your carbs while on vacation (you wouldn't want to lean 'em out at 30') and then have to do it all over again a week or two later.

[Bruce Palmer]

At 5,000' if they are fat and blubbery I'd take both nozzles up a half turn and see what improvement you see. Go 1/4 turns from there if needed..... Remember how many total turns you do going higher in elevation so you know how many to take back out when you get back down to the village from whenc you came.....

[Jetaway]

At 5,000' if they are fat and blubbery I'd take both nozzles up a half turn and see what improvement you see. Go 1/4 turns from there if needed..... Remember how many total turns you do going higher in elevation so you know how many to take back out when you get back down to the village from whenc you came.....

Thanks all!

I'll be puttering, not storming (as I keep telling myself, we'll see how it goes) so I'll have plenty of time to feel and smell the fuel mixture. When it looks as if I'll be above 4000 for a day or two, I'll take Bruce's suggestion and lean out 1/2 a turn and leave it at that unless it really starts screaming for something else. No sense filling the noggin up with fractional additions while on vacation and I can certainly remember 1/2 turn on the return to my little burg. Village, hrmph. We got a Target _and_ a Best Buy. And a Wal-Mart. Village ...

Thanks again, and who knows, maybe a wrong turn at Albuquerque will put me through Salem.

Chris