Carb synchronization...
 

My TT600 factory manual specifies a 7mm primary slide height for engagement of the secondary carb, but further specifies that at full throttle, the butterfly valve in the secondary should be horizontal. I have looked at my TT600 and XT600 carbs, and on neither does this happen; at full throttle the valve plate is easily 2-3mm above horizontal. In both cases the only way to get the horizontal position is to adjust so that the secondary opens at 10mm+ on the primary slide.

I defaulted to the 7mm height, but having the valve past horizontal seems like it would obstruct airflow. What gives?

When the secondary throttle plate is horizontal check that the bottem edge of primary slide is flush with the top of the carb bore. I belive this is what the manual is refering to. I ussually set the carbs at 5mm, As yamaha changed the spec in 85, I find it helps with the 3500rpm stumble that is common problem for the bike.