Need to rejet Ninja 500R - got some questions

[Gadjet]

I just pulled the plugs (without having done much riding with the airbox mod) and they are brownish-copper colored with no visible deposits.

Would this indicate the mixture was too rich before?

Sounds like a fairly normal plug color to me. If the bike was running too rich, the plugs would be black in color with soot deposits.

[jfeaz]

So if the bike wasn't running rich, how would I explain the power loss between 0 and 7500 feet? I have been riding every day for several months, so it should have been plenty of time to damage the plugs.

[flynrider]

So if the bike wasn't running rich, how would I explain the power loss between 0 and 7500 feet? I have been riding every day for several months, so it should have been plenty of time to damage the plugs.

That's no mystery. There is less oxygen at 7500 ft., which means your engine will make less power. This is made even worse in the summer time because the air becomes even less dense as it gets warmer.

Bikes (and cars) that have carbs tend to run richer at altitude which causes even more power loss. You appear to be OK in the mixture dept., but there's not much you can do about the power loss due the the thinner air. On a 35 degree day at 7,500 ft. you can expect the engine to make about 25% less hp than at sea level. On a 90 degree day at that altitude, expect 35% - 40% less power than at sea level.