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fastjeff

fastjeff

Gold Medal Contributor
"Mid-90s Merc two cylinder two

"Mid-90s Merc two cylinder two stroke (Yamaha designed?), 39.6 cubes. There is a 30 hp and a 40 hp version of this same motor. I looked at the parts for both to see where the 10 hp difference comes from. The carbs, intake manifold (reeds), and the block have the same part numbers, as does the driveshaft housing tuner.

What gives?

Jeff"
 
"Yep - all the same except for

"Yep - all the same except for the main carb jets - .054 in the 30 and .066 in the 40 (about 5 bucks for the jet - so you can change a WME-63 to a WME-66 carb for $4.65)

and the other minor difference is on the reed stop specs, so the reed "retainers" are different as well (but that's only a 3 dollar part).

The combination of the jet and reed restriction cuts out the 10 horses. Simply swapping out the reed retainer would turn the 30 into about a 35 horse.

In the models that followed they only made it in the 40 horse version but called it the 30 Jet if they put the jet-drive lower unit on (which reduced the effective shaft horsepower to about 30 when you convert the "thrust" to horsepower)."
 
"And yes, this was the Yami sp

"And yes, this was the Yami split-block "headless" designs that Merc used but Yami never did (at least as far as I have seen)."
 
"Fascinating! I guess it'

"Fascinating! I guess it's easier to make a 40 into a 30 than the other way around.

Thanks, Graham.

Jeff"
 
"All the mfg's did that to

"All the mfg's did that to save money in production, usually with restrictor plates or a different reed cage - usually a Merc is the toughest of the bunch to "hop" up - this model is one of the few exceptions."
 
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