Carb problems !!!! had them for years and normally number 1 ! . This for me was nothing to do with altitude. Just over fueling. I've done that much work you would not believe it. I have just posted in projects what I'm up to. I have tried everything. Now going down a different route, because I have tried everything else.
I've had this problem for about eight years now and getting really annoyed with the bike now. Even had members of the local bike club round here, checked everything on the carbs. Still don't know what it could be. I have owned 100's of bikes over the years not one had a un-fixable problem. No one can sort out this problem out !