Motorcycle Repair: Carb problems, plug colors, right cylinder

Question
I own a 1974 Yamaha TX500A that I'm in the process of trying to fix.  It runs great in the right cylinder but runs very rich in the left cylinder.  There is no power when riding unless I just turned on or off the fuel to the left carb.  Would this indicate that the float level is too high in the left carb because after turning on or off the fuel, the level drops temporarily to the correct height?  Because it runs great when I mess with the fuel I'm convinced it is only a carb issue.  What do you suggest?

Answer
Mike,

sounds like it may have a bad or dirty float
needle valve in the left carb.
-Have you checked the choke and air filters?
-Probably the fuel level changes when you
turn off the gas and it gets a leaner mixture
temporarily.
-The tx500 has been  sensitive to fuel issues since
new for some reason. Keep an eye on your spark
plug colors until they read light brown.
-Check for any loose jets in that carb also.
-check compression on both cylinders.