Aye chapsta, when rebuilding a 4 stroke usually you test the head [ valve seatings] by turn head up. and pour fuel into the head, to see if it leaks by the valves, when you had the head off , you shouda ground the valves ,= better compression ,
You need a compression test now,,,this will reveal all.
Anyway, you did 4000 miles,,did you check the oil level in this time,?