For years I thought 50:1 gave more power than using more oil. It just felt that way on most bikes because the bikes I was riding were not properly jetted. Finally someone jetted a bike for me and showed me how, and I learned that there is not much difference in power with any ratio IF the bike is jetted for that specific ratio. I normally use 40:1 these days to kind of strike a balance. My thinking is that if I jet for 40, and then need to bum gas from a buddy who uses a different oil or ratio, or for some reason use a higher or lower ratio than normal I probably won't foul a plug or have any problems using anything from 32-50:1 when jetted between the two. 40 just seems like a good all around ratio to me. You think you'll never need to use gas from another guys can? I got to a gas stop in an Enduro and someone had used all of my gas! That's when I learned to mark my can, especially if it looked like many others on the trailer. Luckily there was a guy there who let me bum gas from his can. He was using 50:1 and didn't have any idea what brand or type of oil he was using, said his dad mixed it I heard the bike knock once or twice when riding a gear high and lugging, but had no problems.
I read a long article by a major engine tuner, I think it was Eric Gorr, who proved with extensive testing that the more oil you used, even down to 20:1, you could jet for more power and get less wear. With that said, he admitted that there was no reason to use more than 32:1 except for motors that stayed on the pipe all the time such as drag bikes or shifter kart motors. And the power increase with 20:1 over 40:1 was a very small percentage that most riders would never notice.
I read that article many years ago, probably in the late 90s, and carbs, engine parts, porting and reeds, oil, practically everything regarding this issue has improved markedly. My guess is that with everything being better now in every way you can get away with less oil?
I raced a KX 500 hard for 4 years in Enduro, H Scrambles, and many trail rides on 40:1 Kawasaki brand racing oil. I drag raced it and rode in big sand dunes, did it all on that bike. I kept doing compression checks and it was always in spec, so I didn't rebuild it or even ring it. Finally it dropped a little compression and the cause was simply the Nikasil coating on the cylinder had worn off in one spot. Piston and rings looked like they would go another 4 years, but the top end bearing was a bit loose which I replaced along with the piston/rings since it was apart. The bottom end bearings were fine. I sold it to a buddy and it lasted another 5 years on the second top end, with the cylinder coating still not replated. That's 9 years of hard riding on 2 top ends at 40:1. The Powervalve never stuck either which was a common thing on older KXs. Is this scientific? Nope. But when I do something and it works, I generally keep doing it. If it ain't broke, don't...
