Super Hot Expansion Chamber

[builtogo]

So hot the rubber mounts baked off last year, dry leaves that get stuck on it start to smolder and last weekend the rubber coupling started on fire! If I hadn't been in a sand pit I would have lost the whole bike!
It's been hot since I got it (used, barely), but not so hot that the coolant boils over. I've retarded the ignition, jetted it richer and it still runs hot, much hotter than other bikes after the same ride. Please someone help me or I'll have to go back to riding my Alpina.