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In article .com,
says...

O.K.: Urban myth or not?

I've heard over and over again that everything is the same on a 7.5
h.p. Johnson as on the 15 horse, except the carb. I also heard it's
not even the carb, it's just the jets.

I have a 1980-ish 7.5 seahorse that just does not have the guts to pop
my inflatable up on plane with two people and a full tank aboard. I
added those wings, which do help, but still just need a little more.

Anybody actually done this carb or jets upgade, or at least seen it
work? Every dock rat seems to have heard of it, but nobody's done it.

Failing that, any ideas on how to squeeze a bit more out of a
two-stroke (short of going 100:1 on the mix)?

Thanks!

DO NOT screw with the jets!!! That is not the answer. You need more
AIR and FUEL!!! Not more fuel. The differance is that the bore (throat)
and throttle plate are bigger in the 15hp carb. Take note they are
not 'Twice' as big. Air flow goes up as the square of the diameter.
If the hole was twice as big it would flow four times as much air.
The differance between the 9.9 carbs and 15 carbs is remarkably small.
Remember also it takes 3 to 4 times as much power to go twice as fast.
Changing your oil mix and getting 7.7 horsepower out of a 7.5 isn't
worth the risk of a scored and ruined engine. I ski behind my 70 h.p.
and I always run 40:1 instead of 50:1 because I run my engine hard.
It's a 1981 and never been apart!! If you want to get 7.7 out of that
7.5 switch to synthetic lower unit gear grease!! It helps!

Bless and best wishes.