Hey you fellas having trouble with wet sumping , try parking the motor on the compression stroke when you are done riding for the day, it covers the crank oil holes with the rod bearing shell, it will cut your sumping by half at least, unless the wear in your oil pump gears, and shaft are really bad, then not much will help, except a tear down, and conversion to the A-65 type heavier spring set up. I am not a fan of any shut off valves at all, NILL, NADA, NO WAY, it only takes once, to ROAST a motor ! ! ! ! As far as using 50 weight mono grade oil, you have to be in a really warm climate, so the oil never gets really thick. The problem I was told with 50 wt. mono grade oil is that it can be so heavy, it can wash out the white metal bush, if you still have one, instead of the roller conversion. I do not know if this is true, but some of the racers here on the forum, would know if thick 50 wt. mono would wash out the timing side white metal bushing. I was told this by a mechanic here in the Seattle area, that specializes in BSA's, we also have cooler weather conditions than average of 90* summer time, like in North Carolina .The weather here is more like the UK climate, with a bit more winter time rain. Most of my riding is in temperatures in the low to middle 70's, and I will use 40 wt mono, but not 50 wt.
BILL