coolant tank would be terminology, the exciters had what i would refer to as an overflow. more of a bottle than a tank in my opinion, kinda an odd shape, should be able to follow a small hose from under the cap to locate the bottle.
the exciters used a 1 into 2 cable for the choke and the flipper for the choke should be on the console just to the lefty of the key switch. flipper was sometimes labeled as "starter". you will want to correct that issue or you will fight cold starts. i remember mine as having round slides, but thats been some time back. no issues to my knowledge with the butterflies except synchronizing them.
sounds like your clutch needs attention. could be simply dirty or there may be some worn parts. neglect can do that. bushings on the rollers, bushings on the weights, along with the sliding sheave bushing and cover bushing can all come to play. open it up and have a look. i may have some parts clutches if needed.