please help i have swapped carbs over but the bike will not run at over 3,500 rpm it feels like no fuel there is abreather on top of r/h carb do i need to block?. the carb looks the same as 3aj do i need to swap main jet or needle hight,or is this pipe not a breather as i have filled the barrel with petrol by connecting this to the tank duh!! and luckily not sending my piston into space the bike runs and starts fine it just dies at 50/60k.this is my first post cheers folks

I am wondering what carbs you have?

This breather is to connect a vacuum-hose connected to the diafragm-valve in the other end. See http://www.stadiumyamaha.com/pages/parts/home.aspx
Select you model, and choose carb.