i too had problems getting the Kr to run well for me when i first got them. But these motors do have a sweetspot that once you get them (which i admit is the challenging part), they have wicked speed.
here are what works:
1. the stock copper springs are way too soft! you can either bend them to 180 deg (slightly less in the neg) or go with trinity purples on both ends. if you go with the trinity, slightly bend the neg side softer as well. too soft a spring causes excessive arching which promotes premature brush wear.
2. do not go more than 15 degs timing in this motor. for some reason it does not seem to like a lot of timing (like a Ti would normally run best at 20 degs). the Kr has tons of top end as it is and i think putting too much timing just takes away torque and power. too much timing will also wear out your brushes quickly as you're making the motor rev excessively. with high timing the motor will run fast .... but for 2 maybe 3 runs max and then its pig! ... and yes, you will dump faster.
3. start to gear this motor 2 teeth down (assuming you use 64 pitch gears, maybe 1 tooth down if 48 pitch) from how you would gear other motors of the same wind.
4. use higher silver brushes rather than the 766s that come with the motor. i use 767s, they just simply give more power but aren't too abrrasive compared to other higher silver content brushes (ie. putnams, 4499s)
5. use good comm drops. i use tribo. just a drop every 3-5 runs.
note this set up works for me in 6-cell TC. for 4 cell, you can go back to the softer copper springs ang maybe less timing.
hope this helps.