Hi, I here have a 39mm carb, which to my opinion is from a 450/525EXC. It doesn't have a hot start. The number on the side is 3900R... I have however no clue from what year. Can someone tell me? Also, what's the funtion of the pipe (to which a hose can be connected) on the side of the carb (see 2nd picture)? Thanks! Frank.