Horsepower

[65Crosby]

I recently bout a 1965 Merc 900 ,90hp Mercury outboard on a 1965 boat and it runs out ok ,but when you give it a full throttle;, it's like it doesn't have the power to push the boat over 10 to 15 mph on the lake.Anyone know why it doesn't go any faster than this.?

 

[Star]

Re: Horsepower

How big is the boat, What is it made of. What type of hull. If the motor rpm goes up and you don't go any faster, you have spun the hub on your prop... go buy another prop.

 

[65Crosby]

Re: Horsepower

It engages into gear and runs ,the boat is a fiberglass Crosby 1965 Tri-Hull 16ft long.The rpms on the engine don't go up like I think they should at full throttle.It actually pushes the boat along ,just not really fast like a 90hp should.We had guys on jhon-boats passing like we were sitting still.

 

[Chris1956]

Re: Horsepower

Sounds like a compression test and spark test are in order. What do the spark plugs look like?


A 90HP motor on a trihull should pop up on plane and give 35MPH or so. The boat is not waterlogged is it?

 

[65Crosby]

Re: Horsepower

No it's not water logged and the plugs look kinda brownish .I bout this boat after I heard the engine run and the guy gave me the motor,boat,hummingbird fishfinder,28lb.troll motor and trailer for $500.00 bucks.Just couldn't turn it down with the good shape everything was in.Does this engine come with a lower and upper water pump.I am new at this and the friend that went with me said it was a steel,not quite so sure now.

 

[Chris1956]

Re: Horsepower

Brownish spark plugs are fine. Can you put a timing light on it and make sure all are firing? Take a compression test to make sure the motor can develop power.

 

[65Crosby]

Re: Horsepower

What do I need to do in order to do a compression check.Like I said earlier,I'm new at this.

 

[Mi duckdown]

Re: Horsepower

If I were you. I would google compresion check on outboard motors. It might be easier, than trying to explain it.
Just a thought.

 

[MH Hawker]

Re: Horsepower

what is the RPM the motor is running at wide open. could very well be the wrong prop.

 

[aussieflash]

Re: Horsepower

Start at the beginning,as Chris said check compression and then Spark on all cylinders.
Also check all wiring and connections are clean and tight.
Look up FAQ section to learn about compression test.Gauge can be purchased from auto store.