247 not accelerating.

Just a note.  The type 247 and the type 299 are snowmobile engines.  As such the aircraft boys have no data to help you with tuning or parts.  You would do better to contact someone in the snowmobile support side.  If this is the original engine as you say then it is far past its lifespan for parts like the crankshaft end seals and rubber bits at the very least.  The carb has a few parts that should be replaced also at a very old age.  To my knowledge there are no spare parts available for Tillotson from Rotax.  

Cheers