Im not sure whats up with my '82, but it hasnt quite been running rite. Im really not a wiz at the rotary yet (little intimidated?). It sounds like there is a large tin can on the exhaust or something, and the engine sounds like its being held back...

(not the shutter valve on carb, nor is it coolant, oil, or anything else i can think of.)

 

Could be several things. Partial loss of ignition, needs a full tune up, timing is off, cat has failed and is restricting exhaust flow. that should give you some things to start with.

 

Verify that you still have spark on all of your spark plugs. Post back with the results...