motor serial # 6635267

Motor was running fine, I then swap from a aluminum prop to a yamaha 25m prop to get more top speed and took it out for a test run, first run of the morning motor ran good and got a 12mph increase on top end which felt great, of course it suffered hole shot, anyways on second run I couldn't go full throttle anymore, it would stall and die if I give it full throttle, I could only give it enough throttle just to go and I couldn't go past 7mph anymore.

I couldn't figure out why it was running fine going 55mph to all of a sudden I can't​ go past 7mph and stall and dies if full throttle it, I looked at spark plugs looks fine, took out fuel pump diaphragm to look at and it looks fine, primer bulb still pumps firm ect..

Any idea of what can cause this?