1984 Johnson 150 gt not running in water

by kal lofton
(whitesboro tx usa)

I have a 1984 tidecraft bass boat with a 84 Johnson 150 gt in it when I have the lower unit out of the water our runs fine I can full blast the throttle and it is 10o percent but as soon as the propeller is submerged it won't I can barely get it to go 2 or 3mph on full throttle just rebuilt the carbs and put a new coil pack on it didn't do this until I put the new coil pack on I don't think that would affect it any thank you