Re: 50:1 to 40:1 question
In mine and most people that have been running these engines for several years now recommend first that you use a high quality oil and second use the manufacturer s recommended mix for that particular oil, the oil debate in regards to which brand is best and what is the best mix ratio will obviously never die on this forum, but if you will do your do diligence and use the search feature on this forum you wll get hours of education on what the long time runners and builders of these engines use and at what ratio they have proven to work great for them.
I run my engines @ 100:1 and I use Opti2 oil which is designed for the ratio, I run my engines hard and at high RPMs the carb needs to be precisely tuned for the oil and mix you plan to run and then you should stick with that mix always unless you retune for a different mix ratio, some of my engines see well over 9000RPM and I have actually torture tested one of them on a wide open throttle run non stop for over 7 miles, this engine still runs strong and smooth with over 500 miles on it now and it has never seen anything but 100:1 Opti2 mix
I have logged several thousand miles combined on three bikes now and they're all still running great and not a single oil related failuresince switching to using Opti2 back in 2010.
There are other good oils out there also like Amsoil, Maxima, Redline, Lucas, the Echo 50:1 synthetic blend oil is another good oil, just make sure the carb is tuned correctly and you decide on a mix and stick with it is the best insurance that you dont have oil related issues do to a lack of or to much oil which can. Ause a lean run condition that can fry your engine.
I dont always ride WOT, but when I do..I do my best to keep the rubber side down..Ride safely my friends!