19cc domes at 3,000 feet will make less compression than at sea level. 19cc at 3k is like 158 psi compression on a stock bore, stock port bike.You cant gauge octane off dome size, its got to be gauged off squish and compression actuals. Your pilot jet is way to huge, you never said what needle is in it, I would think that main at 3,000 ft would be too rich. Did you try swapping the plug wires side to side to see if the problem changed cylinders? Exhaust port height will also change the compression reading.