1992 Yamaha TT 350 float height

The service manual says 27mm +/- .5mm to answer the question.

it will start and run on either float level but will not carry load or high rpms
your statement that it requires a choke ( blocking air intake) to start indicates a assembly problem in the carby/s
blocked main jets, idle circuits
it could also be a fuel supply problem to the carb/s
(filter , lines, taps) it could be possible that the float action is wrong and the float is in a down position and blocking off the needle and seat as if the bowl is full
the float setting will be available on the net
go google and enter-- float setting/adjustment for yamaha 1998 v star motor cycle ---
look also for a workshop manual for the carby/s make on line to check assembly correctness

Pull the carb off.Take the bowl off,take the pilot jet( the small one )out and clean ALL the holes out where you can see through it and the side holes.Then take out the main jet and make sure it is clear.Reinstall every thing and dont bend any parts on the float or the needle vale.