Mercury 3 cyl 40 HP hop-up

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Cajuntroutslayer

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Feb 17, 2009
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In 2000, while shopping for a new 40 hp outboard, I opted to go with Mercury. Mercury used the same displacement for their 40, 50, and 60hp engines. A very common thing to do here in South Louisiana is to install carbs from a mercury 60 on the mercury 40 (We have some marshes that limit horsepower at 40). I finally got around to doing this last Spring. The increase in power is unreal. I went from a top speed of roughly 36 to about 41 mph on GPS, (I even had to re-prop). This is on a 16' x 52" Alweld semi-v.

This increase in performance comes with a price - FUEL! My fuel economy has almost cut in half since doing this.

I noticed since I did this that the engine smokes a lot more. The spark plugs look pretty good, but I was thinking about jetting down to the next size.

Any comments from the 2-stroke gurus are much appreciated.

Thanks,

Todd
 
L

Laddies

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Sep 10, 2004
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Re: Mercury 3 cyl 40 HP hop-up

Even though you got a increase in speed there are some differances in some of the exhaust systems thats why its running rich. You need to lean it down just don't go to far or you will need a powerhead.
 
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