Lately I have been noticing when I first start up my BMW 1985 KRT100 it does not want to idle and if it stalls, it becomes hard to start, unlike when I first get it started, it fires right up. Then at high altitude (over 7000 ft) when I start it after it has sat for hours, it will hardly run at a very low rpm regardless of throttle setting. After it warms up in this condition it returns to normal. Anyone familiar with this issue or what it could be?