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2 stroke 3 cyl HP ratings

S

Steve in sunny Fla

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I see the 60, 75 and 90 all share the same bore / stroke, so I'm curious about what is limiting the hp in the 60 and 75 hp engines? Is it strictly carb size, or also port timing? Is the 75 just a 90 with smaller carbs and less ignition advance?

TIA,

Steve
 
exhaust port height and carb venturi size. They made 2 different bore in these motors. The earlier motors are more carb/height specific. The newer ones are not as much as the 75/90 is same block just carbs
 
faztbullet said:
exhaust port height and carb venturi size. They made 2 different bore in these motors. The earlier motors are more carb/height specific. The newer ones are not as much as the 75/90 is same block just carbs
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Thank you. I have a 2008 90 elpto. I have it running great, 36 mph on a 17" prop which is slightly over rev (Yes I have a tach, but I think it's about 400 rpm low when the math is applied) however there is what I consider significant throttle left at peak rpm. I'm wondering if a set of carbs from a 75 would be more appropriate and deliver better economy. I do have a good understanding of carbs / jetting, but no boat / outboard / 2 stroke experience.

Opinion on smaller carbs?

TIA, Steve
 
Go to the Mercury Marine parts catalogs. Look at all three same year models. You will be able to determine the part number differences. Knowing that, you can make an educated guess as to how one model is making more, or less, power than the other model.

Some times it is the carburetors, the CDI box, the air intake system, etc..

You are the first that appears to want to do down in power. Others always seeking more free power.
 
I suppose you know that a motor that can make 90 HP will make less power with less throttle. Lot cheaper than replacing carburetors.
 
boscoe said:
I suppose you know that a motor that can make 90 HP will make less power with less throttle. Lot cheaper than replacing carburetors.
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You're correct that less throttle on large carbs is less power, but smaller carbs don't always mean less power. My point isn't to go down in power... but with a pretty significant amount of unusable throttle, smaller carbs will deliver better fuel economy and be more responsive. Trust me, being a lifelong hotrodder is akin to being like any other addict... my brain just isn't like "normal" people.

Steve
 
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