The stock 636 brakes are excellent units that don't really require stainless lines or different pads. The radial master cylinders however, are a PITA to bleed properly. And I mean PITA! Try removing yours from the handlebar and rotating it about and or tapping it with a plastic mallet to drive any air up to the bleeder nipple. You can also pinch the feed line from the reservoir while bleeding in an attempt to suck any air out of the deeper parts of the master instead of just getting new fluid from the reservoir. Spiegler
has a banjo bolt you can replace the stock item with that has a bleeder in it as well. Some people have said that's the trick, although I haven't tried it myself.
I personally folded after constantly fussing with mine and never quite getting it right, and had Dave Moss at Feelthetrack
bleed mine. He's a wizard is all I can say. If you happen to be in Northern California, I'd tell you to go see him, and have your suspension adjusted as well.
It's not how fast you go, it's how little you slow.