You know, think 'm going to switch to M1 10w40, and 'll tell you why. When i first put this M1 20w50 in the bike ran better. I could feel s definite and nice improvement in power apparently due to the better slickness of the M1 over the torco blend i had in it B4. But after a short time that extra oomph was gone and i believe i know why. theres a oil forum where the members are fanatical about motor oil and they seem to know all the latest details about various oils. I was hearing a lot about mobil having changed thier formula not long ago and i asked about it. I was told that in some oil comparisons, M1's new formula showed that thier oils viscosity actual went UP after a few miles, maybe a few hundred or some such thing. (don't recall exactly) So the 20w50 went up from 50 weight to 60 after the oil had some miles on it. This would make total sense from my experience. I figured the My full synth was slicker than the torco blend and also just a very good synthetic, so i figured that was the reason for the power increase. But when it went away soon all i could think was new oil is slicker and after a time it wasn't as slick. But if that was the reason the power diminished, why did i never notice a increase in power when i changed my oil in the past to the same oil used in the last change? then i read about M1 bike oil's new formula increasing in viscosity as it aged and it made perfect sense.
So while i can never be 100% sure, it does seem likely so i'm going to try 10W40 next time and hopefully it will run as well as the 20w50 did when new even after it has fully broken in.