You can get a complete new carb for $25-$30 on ebay, easy to find. You could reconfigure everything and keep the 200s motor, not that big of a deal unless you really really want a manual/hand clutch type motor. I like the autos myself, but i know its not everyones liking.
You could get the 200s service manual to see the routing of the breather hoses and stuff like that, as it would be in the correct frame. You should have that service manual anyway for the motor. Smoking could be one of two things... I assume you mean blue smoke as in burning oil. Either the valve stem seals or the rings. If it sat for a very long time the cylinder could be rusted up and it will wear in after a while and stop smoking, been there done that on a few old trikes that sat for years. Usually when i get one that sat for a while i dump some oil down the plug hole and change the oil and let it soak overnight, then slowly turn it over by hand a few times before running it, then run it without much if any revving, just let it idle for a while, see if it clears up, then change oil again to get the crap out. Sometimes i get lucky, sometimes they still smoke some. The 200's also like to smoke a bit after they sat and oil seeps down past the valve stem seals overnight, then the next morning you fire it up and get smoke for a little bit and it goes away after riding it a bit, good sign that its a valve stem seal leak.
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1984 Honda ATC200ES "Big Red"
1982 ATC200E "Hondie"
1988 TRX300FW "Project Quad" Still in progress....