i recently bought a 1996 kachina with a 454 bored .30. Guy said had 6 hrs on a new motor. I was going about 30 MPH and the engine made a few clunk sounds and died. Looked in pump didn't see anything. Took plugs out and since it died on lake it cliks once loud and motor will not turn or try to turn over. Do u think motor is locked up? I did get on it hard about 8 times for about 5 min each time. Has a dominator pump and read u can't disconnect without pulin engine. Any thoughts on what my problem might be

Well  I'll add my 2-cents...even IF you haven't hurt the motor.  Unless you have an engine set up for enduro racing...."Running it hard for 5-minutes ( & assuming that lot's of wide open  )....IS like running on a dyno for 5-minutes. All boat engines are under constant load. You may be cruising @ 2500......but that's not like 2500 in your car. OIl temps go crazy with a stock oiling system...never mind the actual fuel mixture reaching outboard cylinders. Main & rod bearings get overheated in mere seconds.....So, if it ends up being something minor...very cool.   But suggest you don't run it that hard again w/o proper upgrade.

Good Luck!