1979 Mercury 40 hp

[schuler1]

I recently bought an older fishing boat and it has a 1979 40 hp Mercury motor on it. I'm new to boat motors so i dont know hardly anything about them. I was wondering if someone could help me figure out why the boat isn't very fast. It will only go about 15 mph. The motor sounds like it is running fine and it starts easy every time. I push the throttle wide open and it gets pretty loud but its just not that fast. I dont know if this is how fast it should go or if their is something wrong. Thanks!!!

 

[TwinMerc500]

Re: 1979 Mercury 40 hp

Id start by checking the compression, it can tell you how tired your old motor is.

 

[schuler1]

Re: 1979 Mercury 40 hp

Alright thanks!! I'll let you know what the compression is tommorow. Thanks again for the suggestion!!

 

[Maddoxsdaddy]

Re: 1979 Mercury 40 hp

Wow... finally someone with the exact same problems i've had. I bought a 1981 Alumacraft with a 40hp Merc on it. First time out, only made 6 mph. My throttle/spark advance linkage was stuck from corrosion because it had been sitting for 5 years. The stator was changed as well. My compression checked out @ 115 psi per cylinder. Then it got to about 15 mph. I went to the fuel pump, fuel lines, new tank, new line from the tank to the motor, and finally a rebuild on the carb. I just rebuilt the carb this past weekend and have yet to try it on the lake yet to see what happens. If i had it to do over again, i'd rebuild the carb right after i found out the compression was good. I'm hoping to go fishing and try it out this weekend so i'll keep you posted as to whether or not the rebuild worked. Hope this helps.

 

[bullbat]

Re: 1979 Mercury 40 hp

also you really need a tach so you know if your engine is operating at the right rpm, could be a number of things causing ti to be slow the prop could be slipping or the engine just not turn the rpm it needs