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Chances are you're looking at a carb rebuild and then what's called a "link and sync" which is the process of synchronizing the carbs with the timing advance. If you are handy, and have access to the factory service manual, both of those are pretty easy and it will not cost you much. If you need to go to a mechanic, be sure you find one who knows older motors.

Don't get an aftermarket service manual - they suck. Only a factory manual will help you do this properly.