it would definitely help. that 5/30 is so thin when its hot. my slant made all kinds of top end noise when i got it because the guy was using 5/30. i put 10/40 in it and it made a difference right of the bat.
AND......................on top of what everyone else said, if you are running a mechanical fuel pump, do not dismiss the possibility that the pump is leaking fuel into the crankcase, diluting the oil
