My 500cc Yamaha was still doing fine at 5,500ft. asl, although running rich. The Dodge Ramcharger didn't like that altitude at all. My F350 Diesel did fine at 12,000 or 14,000ft. asl or whatever the continental divide in the USA is. I was pulling a trailer at 120kmph as well so, a specialty vehicle also with computer and variable air/fuel mixture, would like work a lot higher.
-------------------- Daryl
"a gun without hammers is like a Spaniel without ears" King George V