Oh one more thing. If that Ninja has stock gearing, going up one more tooth on the front sprocket will make everything a lot better. The older Ninja 250 was one of those one in a million bikes that really was undergeared. Going up to a 15 tooth front sprocket will help on both the top end and the bottom end. It's better everywhere, no sacrifices anywhere.
2002 Vulcan 750 (now being slowly reassembled) 2013 Royal Enfield B5
2001 XT225, 2009 Genuine Stella
1980 Puch moped