Help with no power! Mercruiser 5.7

[LarsonKid]

Hey guys. Got a question about my 235 Larson Hampton boat. The engine seems to be running fine but when I give it throttle is develops a rattling noise and I can’t pick up any power to plane. After a little while it will eventually plane and run fine. When I give the engine just throttle without putting it into gear it sounds perfect and has no rattle what so ever. I’m wondering if it has something to do with the prop. Any help would be greatly appreciated as it’s the first day of our vacation and we already have some issues

 

[Scott Danforth]

what year mercruiser
serial number helps

could be bad gas or improper timing and the sound you hear is detonation which is your motor eating itself

 

[tpenfield]

Can you post a video of the 'rattling' , etc. ?

 

[LarsonKid]

I’ll try and get a video tomorrow and it’s an 1997. On our way back in to the dock it would die out when idling. So now I’m starting to think something gas related for sure.

 

[Bondo]

I’ll try and get a video tomorrow and it’s an 1997. On our way back in to the dock it would die out when idling. So now I’m starting to think something gas related for sure.

Ayuh,...... Get a new filter, 'n a qt. freezer baggie,.....
Loosen the filter, slip the baggie 'round it, quickly, then spin the ole filter off, droppin' it into the baggie,.....
Don't drop the baggie,....
Seal up the baggie, 'n flip the filter, upside down, 'n examine the filter's Contents, for anything but clean fresh gasoline,.....

Whatever else that's in there is causin' yer motor to self-distruct, from detonation,... the pingin' yer hearin',.....