Can I change my 75 horsepower Mariner to 90 horsepower?

[starkyb]

I have a 1988 75 horse 3 cylinder motor. I know that some of the parts are interchangeable but is it possible to increase my motor to 90 horsepower? Would it be easier to just try to trade up and buy a 90 horse?

 

[Faztbullet]

Re: Can I change my 75 horsepower Mariner to 90 horsepower?

Sure all you need is the is the 90 hp carbs and raise the exhaust port timing .110... I myself would trade up to a later model big bore engine.

 

[starkyb]

Re: Can I change my 75 horsepower Mariner to 90 horsepower?

According to the parts schematic, the carbs are exactly the same. How do you raise the exhaust timing? My daughter just started college, I don't see a new motor in my future.

 

[sschefer]

Re: Can I change my 75 horsepower Mariner to 90 horsepower?

According to the parts schematic, the carbs are exactly the same. How do you raise the exhaust timing? My daughter just started college, I don't see a new motor in my future.

Go ahead faztbullet, you started it..

 

[Faztbullet]

Re: Can I change my 75 horsepower Mariner to 90 horsepower?

According to the parts schematic, the carbs are exactly the same.

The 90 hp carbs are WME-5's and the 75 are WME-6, the differences being the cast in emulsion tubes and idle port pockets otherwise they look the same. To raise the port timing you will need to remove and disassemble powerhead and take to a machine shop and have ports raised on a Bridgeport mill, you can do it by hand it you make a pattern from a split sleeve that been hardened so you dont take to much..

 

[wired247]

Re: Can I change my 75 horsepower Mariner to 90 horsepower?

According to the parts schematic, the carbs are exactly the same. How do you raise the exhaust timing? My daughter just started college, I don't see a new motor in my future.

Port timing on an outboard means the position of the intake and exhaust ports in relation to the top or bottom of the cylinder walls. Higher HP engines usually have ports positioned higher on the cylinder walls if all other things other than carbs and timing are equal. I have a 150 Mercury. It is the same displacement as a 200 or even a 260 Mercury but the ports on those engines are positioned higher and are wider than mine. To change port timing you would have to disassemble the motor and raise and or widen the ports located in the cylinder walls either painstakingly with a file or with the files bigger brother, the vertical mill . Carb jetting and ignition timing changes are usually just to compensate for the timing of the ports and are not means to themselves to HP increases.