Chances are it has varnish in the tank, and carbs, and likely it has deposits (varnish, carbon, and ???) within the crankcase, and the transmission. First things, first.
SeaFoam is your friend: add it to the gas tank, as per the can's instructions, run it for two minutes, to circulate it through the fuel system, then shut it off, for a day. After that, take it out and run it to fully flush the treated gas through the engine.
Add
SeaFoam to the crankcase, as per the can's instructions: run the bike, idling, for five minutes; shift through the gears, letting the idling engine spin the rear wheel, as this will circulate it throughout the engine, and the transmission. The
SeaFoam will likely turn your caramel-colored oil, black, in the space of five minutes of run time -- change the oil, and the filter, to remove the crud.
If you did not change out the fork fluid, it needs it. You can use expensive Fork Oil (pick a weight, the higher the number, the stiffer the front suspension will be; around $15/quart), or your can use Dexron III/IV/V ATF in the forks (supposedly has a viscosity of 8; costs around $4/quart; specified by Honda for use by default; softer fork response to bumps).
It will need to be tuned up, carbs adjusted, and balanced: see the Home Page for links to a video series on how to disassemble the carbs, clean them, and then re-assemble. Download the Factory Service Manual (FSM) from the home page. Get back to us with specific topics you need help with. Cheers!
1979 CB750K (sold, 2012, but not forgotten)
1983 Kawasaki 440 LTD Belt Drive (sold, 2011)
1993 Kawasaki Voyager XII