1989 js650 won't rev/Boggs down
 

I purchased a 1989 js 650, and its having a few problems which I can't work out. It starts fine and idles fine, but when I pull the throttle it doesn't rev like it should, it coughs and splutters and smokes (white smoke). While in the water, it Boggs the ass down and smokes.
I've put oil injection block off valve
Crank case block off
Reeds are fine
Rebuilt carby
New regulator/rectifier
New starter solenoid
Second hand CID unit
New plugs
New fuel
Checked all fuel lines - all good
Any ideas would be very great full.