merc 9.8 wont go fast

[yut]

I have an early to mid 70's mercury 110 9.8hp outboard. It sits on a 12' aluminum boat. The motor starts and idles real good. It will rev up pretty high in neutral and in reverse. But when I put it in forward gear at full throttle, it sounds like it is only half throttle. It revs and runs smoothly at full throttle even. The top speed of the boat is probably only about 5 or 6 mph. I was told that motor and boat should reach around 15 mph. Does anybody have any ideas?

 

[tashasdaddy]

Re: merc 9.8 wont go fast

sounds like you have a fuel restriction, when were the carbs last cleaned. did it sit over the winter with gas in the carbs. have you check the compression?

 

[Laddies]

Re: merc 9.8 wont go fast

That sounds like a dirty high speed jet, have you cked for spark on both cyls? That can also act that way, if you have spark then you will have to clean the carb.

 

[Yepblaze]

Re: merc 9.8 wont go fast

Maybe someone has replaced the propeller with the incorrect one.

 

[CharlieB]

Re: merc 9.8 wont go fast

With the engine turned OFF put it in forward WOT
is the throttle linkage opening the carbs fully?

 

[Ryan's outboard]

Re: merc 9.8 wont go fast

I would get a can of sea foam about 1 can for 5 gallons and run that through. It really picked the speed up on my 69 merc 110. Also, I had a problem with the propeller being so old that the rubber seal on the prop wasnt gripping, so I gradually lost speed and then after about a year everytime I gave it full throttle it would just spin so I could barely move. I believe they wanted $40 to rebuild the prop including that rubber gaskette. but I would do the the sea foam first as its only about $5 a can.