High altitude mixture observations

Just got back from Deadwood where it was fun to meet some of the folks on the Forum. There we drove at altitudes of 4500 - 5800 ft.

I'm running Normal UH needles in my HD8s. Referring to my Air/Fuel Ratio gauges, 11s to 12s were typical. 11 is just on the rich side of power; power is 12.1 - 12.8.

One warm day in traffic at a tunnel at 5800 ft, the plugs were loading up a little, but cleared up as speed was resumed.

I seemed to recall that some folks who live at high altitudes had been advised to use the rich UN needles and wanted to report back that my instruments told me otherwise.

FWIW at my normal altitudes of around 1000 ft, the car runs a little leaner in the 13s on the freeway.

Steve, I don't have much altitude variation in my area of Pa. So I don't have a lot of experience with how altitude affects the Healey. But, I thought as the air gets thinner with altitude then the carbs would richen. Why then would anyone want to put richer needles in when they drive to higher altitudes? Or do I have it all wrong.

Nope, you have it right vette. Higher altitude = less oxygen, so to compensate, you need to lean mixtures.

Steves experience is what I would expect. It's just that in most cases people don't have accurate A/F gauges to show it.

Dave

I posted this as I seemed to remember a certain person who lives at one of the higher elevations had been advised by a certain supplier to use the rich needles. I could be remembering wrong - backing up a general observation with data.

Good data Steve. Thanks for sharing.