Just bought used bass boat with according to title 1979 150 Max, cowling has 175 black max, put it in water yesterday started fine. Warmed up! When I got into it planed out but when rpms got above 5000 it just shut back down to idle, did not die. Brougt throttle back to netureal tried again same results. Did this several times, finally out of frustration kept about 4000 rpms everything fine. Any suggestions would be appreciated.