I have a ZXI900 that’s lacking top end power. Mechanically all is fine, compression is 120 in all 3, carbs are clean and diaphragms are all intact, fuel is clean, new and premixed at 40:1. The problem is that once the ski gets up to above around 5000rpm it seems to run out of puff. It chuffs out copious amounts of smoke as well. Im assuming that the problem is the high speed mixture settings. Ive reset the high speed screws to the factory settings (3/4 +-1/4 turn). I started at ¾ and it didn’t make any difference. I then set all 3 of them at ½ turn (3/4 – ¼) and it is better but I think it needs to go leaner. A ½ turn out is the leanest that the manual says to go and im afraid that if I lean it out too much I’ll start melting things. Any advice on how far in I can lean it off before I do damage? Is there a procedure to get the settings correct? I’d appreciate any advice you could give me.