I was at a local AMA race last weekend, and there were a number of 636 racers and talked to all of their mechanic and engine guys about that. I bought a case of mobil 1 15w50 and was waiting until 2000, but they all said that on a street bike, 1500 mi. was alright. I have 1250 and am waiting to get to 1500, then change the filter and go to full synth from petroleum oil. I wanted to go to semi-synth, but I can't find silkolene semi-synth around here, and all the rest are questionable on how much synth is in the rest from what I hear. So I'm going to ful synth at 1500 mi.