Our rev limiters make it impossible to tune the way I learned how way back in the day but I agree, once you hit peak RPM, it's on the edge of too lean and you need to give some back, to remain on the safe side of the ratio. 50RPM is a good compromise, it's just enough to notice.
I think all factory settings or slightly richer by a small amount is good, especially if it feels too lean give it more. I like to hear some occasional four-stroking in the low end, it's tough tuning the top end b/c of the rev limiter and the old method doesn't apply any longer due to these electronic rev limiters but an unloaded motor should four-stroke at WOT, like when the pump comes unhooked(Rev limiter must be disabled of course, four-stroking unloaded WOT was our rev-limiter from back in the day). The first generation of rev limiters actually were mechanical and fitted into the carbs (called mixture governors), we used to disable them so we could properly tune our 2-stroker motors.
Seat orifice of 951: If this is a 951 using the BN-46i, the 1.5 seat won't flow enough fuel and the top end will be too lean, DON'T do this! Use the 2.0 seat along with the proper 95 gram spring. I actually sneeked an 80 gram metering spring in mine and found it's a hair too rich with my larger pilot jet but still works well. Be careful though, being too rich in the low end can be a dangerous combination with an injection system due to there is no oil flowing during low speed idle operation but, I don't idle exceptionally long distances anyway so my crankcase probably can't run out of oil.
Needle valve: 2.0 p/n 78635015-2.0
Arm Spring: 95gr p/n 730-03027-T Silver, reverse wound
Something's probably wrong if the factory settings won't run acceptably, my 951 ran okay but was just too flat for my liking in the low speed nearly up to 70% throttle thus I increased low speed pilot jet size.
