Oil tank on the left and round section swing arm, thats an early one. It should have a carb as follows
Mikuni VM24, Number 2H500
Standard Set up with factory porting, standard exhaust and air filter
Throttle Slide, 2.0
Needle, 4j13 Clip position 3.
Needle Jet, 249 0-2
Main Jet, 130
Pilot Jet, 25
Reed side diameter, 35mm
Filter side diameter, 43mm
Length, 85mm
Float Height, 21mm
Sounds to me like its running rich, it gets worse with choke so isnt lean, if fuel is running from the overflow then the level is too high, this will cause a rich mixture and may lead to (four stroking)...firing every other rev instead of every rev. you need to re check the float height, as I posted earlier, did you check from beneath the gasket and with tang only touching the needle valve without compressing the spring? Perhaps the float needle valve is worn and is passing fuel, examine with a magnifying glass for wear around the pointed end. Rather than test on a paddock stand you would be better riding it to test as its under load then. besides its safer and wont have your chain whipping about so much.