78 merc 115 top end hesitation

[kevlar3000]

This is on behalf of a friend. He has a 78<br />115 Merc on a 16 ft V. It starts and idles great. At the top end speed it can hit 52 mph. On occasion with no apparent reason the boat will top out at 46 or 47 with an rpm loss. It then will kind of click in to normal top end speed and stay there for the rest of the day. Or sometimes it just stays<br />at the lower range. This could last for 5 minutes or an hour or.... No specific trigger to what is going on. There are no knocks or weird noises, it just slows down. But once it kicks in at the higher end it seems to stay there. Any Ideas? ODDD1 if you see this it is separate from my 1150 that you were so helpful with.

 

[ODDD1]

Re: 78 merc 115 top end hesitation

Hey,kevlar....if he is dropping 800 to900 rpm's.....probably losing a cylinder......first thought i had was a bad switch box dropping spark on one cylinder.....if he has boxes with an "A1" after the part number they are origanal an suspect.....tell him good luck for me.......intermittents are a pain.....