97 Nitro 75hp Merc won't plane out

Hi..I recently took my boat out on a lake and it ran perfectly for two days.After a few hours,and a brief rainstorm,I took the boat out again and it would not plane out.With the throttle wide open,it would only get to 4000 rpms.Was hoping the next morning all would be well,but the same thing occured.I did leave the boat parked in the water entire time on trip(3 days),and the prop did get in the sand,but only on the surface.Also,while there,I used 89 gas from the marina,while up to then I had only used 87.The oil mix is 50:1.Could anyone tell me what may be the cause of sudden loss of power and could any of the factors mentioned above be a contributer.Any solutions would be greatly appreciated. Thanks for your time.

Re: 97 Nitro 75hp Merc won't plane out

i had a 1990 mariner 60 hp that did the same thing.what happened was the bottom plug went dead,simple as that. i put in a new plug and away she went to full rpm and plane.you might have a dead plug. do you have the sureface gap plug in this motor? they are prone to fouling up if used for trolling alot like i did. i read somewheres that you could replace these with the standard style pugs if you get the correct ones.at the very least greg put in new plugs and id bet your problem is over unless there is bigger problems like a coil or? but im betting on a pooched plug.

Re: 97 Nitro 75hp Merc won't plane out

thanks for your time Cougar,I'm gonna try that .

Re: 97 Nitro 75hp Merc won't plane out

changed the plugs,ran great...thanks a lot