I think a 14" prop is too much for a .75 size 2 stroke engine.
I pushed past the manufacturers recommendations with a 14x8 on my ST.90.
I would suggest 12x8 to 13x6
Here is tower hobbies page for their .75
http://www2.towerhobbies.com/cgi-bin...?&I=LXUR78&P=0