[Jeff Higgins]

There is a barometric cell located on top of the pump (small CAD plated canister) that is supposed to provide for altitude (or other barometric change) compensation. I am not entirely sure what its range of compensation might be. On my car, tuned at sea level, it appears to be well outside whatever that range might be when I drive the car at high altitude.

I made about a 4,500 mile loop down to Sante Fe (I'm just north of Seattle) last May for our annual club Treffen. We travelled over three mountain passes of roughly 10,000 feet elevation. My car ran extremely rich at that altitude, with little power. The affects were felt at lower (5,000-6,000 foot) elevations along the way as well, but I kept thinking this was a temporary situation anyway. In retrospect I should have leaned out the main rack a few clicks, then just reset it when I got home.

At home, with our passes running more in the 3,000-4,000 foot range, I can get over them just fine with my sea level tune. I wonder if that might be about the limit of the altitude compensation offered by the barometric cell.

So, yeah, living at higher elevation, I bet this is as simple as leaning your pump out to a different "nominal". If you ever travel to, and plan on spending any time at lower elevations, it would be worthwhile to richen it up for such a trip. In my case, going from lower to higher, it just goes blubbery rich and robs power and mileage. In your case, going from higher to lower, it could wind up dangerously lean.

This is a very easy adjustment to make. It's worth getting comfortable doing it yourself, if you travel across widely varying altitudes. Just make note of what you did, and return it to your "nominal" when you get back home.