Do I add or remove shims on the altitude compensator on a 1971 280SL? The car runs great but is very sluggish at this altitude and I'm just trying to improve it's performance somewhat. It surges slightly at 60 mph but otherwise runs great. Just very slow. There is no soot coming from the tailpipes. I bumped the timing to 18 degrees w/vacuum off which helped. I may go to 20 degrees because at this altitude it won't ping.
