Ran badly at altitude today. Advice?
Rode my 2003 up the mountains today. Ran just fine till I got to about 10,500 ft. There's a 15% + grade and I was WOT. Bike started surging and temp gauge got just to the low end of the red bar. Stopped as soon as I could let it idle till it cooled a bit. Ran great downhill and for the rest of the day at 8000'
Cooling system seems ok-stays cool at 105 F at 5000' in traffic.
Not sure about PO mods but the pilot screw cap hadn't been drilled out, so suspect 22 cent mod hadn't been done. I have backed out the mixture screw to 2 1/4 turns from 1 1/2 & it runs fine at part throttle below 10,000'
So I'm puzzled. It acted like it was running lean (surge & overheating) and at WOT I wouldn't expect the mixture screw to be doing much.
What should I investigate first?
Thanks in advance , Wray