Took the freshly rebuilt 750F on a ride today, it just broke 100 miles on the new engine and its running wonderfully! The break process in is killing me though I cant wait to rev it over 5,000 rpm's 
I waited max 20 minutes to rev past 6000rpm

I have old pistons (Action Fours 836) I can look at that got a too soft break in. Not passing 5000 rpm the first 1000km.
They have brown residues under and around the rings as described will happen when not let it grind in the rings the important first 100-200km (when bores are rough like sandpaper) by heavy decelerations reducing throttle completely a several times from 4000, followed by 6000rpm.
My later used 836 and 1000cc are shiny. I had read about break-ins and why to not be too light on the throttle.
The 1000cc got a quick trip to 8000 rpm too at first ride when really warm and whipped by several decelerations. Too fun;D
My stock K2 with K7 61.5mm pistons got a similar treatment. Run it warm and easy the first 10-20 minutes, 4000rpm, max 20 minutes later 6000 rpm bursts. Not for a longer period though. 7000rpm at 2nd ride, from 150km

Steady cruising in 4000-5000rpm with heavy decelerations.
8000rpm after 200 km and really warm engine.
Important to let it rev 2000rpm at first start to quickly ensure oil pressure at top end is my thought.
I wonder how the race guys do?
