evinrude 9.9 to 15 hp conversion?

[eli]

Worth it ,I put a carb from a 25 on buds 18 picked up 7 mph

[Motv18]

Some also have a different reed setup

compression test some some older ones are already at or near 140 psi which puts you running 91 well.

Theirs also some timing optimization to be done. And a tiny tach to prop right.

[Nitro25]

Look at a 1979. Tuner is the same. Carbs are the same. Carb bore the same. Reeds the same. just put a 15hp jet or file out the stock jet to a 15hp size. Try it you'll like it.

[Motv18]

Did the 79 also have a different rpm limit

out 15 rental always seen to sound higher then the 9.9 rental

[Nitro25]

Don't know! Your testing my memory from 39 years ago! Have to see a manual. But I know it worked back in that era, because I did it to make my jerk managers son get beat by the Marina owners Daughter with identical 8' Hydros (Play toys) During a video shoot to market these little boats no less.

I think I got a raise after that...?

That was a fun day!

[powerabout]

Look at a 1979. Tuner is the same. Carbs are the same. Carb bore the same. Reeds the same. just put a 15hp jet or file out the stock jet to a 15hp size. Try it you'll like it.

no such thing as 2 horsepower models and the only difference is the main jet.
OMC main bodies are NSS so there is no part number to check

[MattGreen]

I’ve done this conversion numerous times. Gary and Power are correct, the 15 carb has a noticeably larger bore and the 15hp tuner is a short cone-shaped casting as compared to a lengthy constricted tube deal on the 9.9. The reeds are the same. I believe there were a couple years where only the carb was the difference but in most model years there are 2 differences. Replace the water tube grommets while you have the tuner off - key failure area on these engines.

If you want to go faster, try these ideas:
1) pick the brains of APBA class 15A racers who run this basic powerhead, and/or
2) if you’re pulling the motor apart to change the above bits, may as well go a bit further and do a fresh rebuild as well unless you know the bores are great. It may even be possible to shoe-horn the 1993-up bigger bore pistons into your block (never tried it).

Matt

[Instigator]

Im not positive on yrs but I think when they came out w/that style cowling is what is effected.

I raced A Stock Hydro in APBA w/a ‘50’s vintage Merc.
They we’re out run and replaced by that motor.

The 15 powerhead in stock form was an “A” class motor.
W/a restricted carb and tuner it became a “J” class motor.
The J class was the entry level, for kids class.
When I quit, 30 yrs ago, the A Hydro Kilo record was mid 60’s.

I saw the future even back then because I remember reading that yrs brochure (whenever it came out) and that 15 had an advertised 7000 RPM rev range.

I had a couple of them on dinghies more recently and could knee board behind them.

I’ve done this conversion numerous times. Gary and Power are correct, the 15 carb has a noticeably larger bore and the 15hp tuner is a short cone-shaped casting as compared to a lengthy constricted tube deal on the 9.9. The reeds are the same. I believe there were a couple years where only the carb was the difference but in most model years there are 2 differences. Replace the water tube grommets while you have the tuner off - key failure area on these engines.

If you want to go faster, try these ideas:
1) pick the brains of APBA class 15A racers who run this basic powerhead, and/or
2) if you’re pulling the motor apart to change the above bits, may as well go a bit further and do a fresh rebuild as well unless you know the bores are great. It may even be possible to shoe-horn the 1993-up bigger bore pistons into your block (never tried it).

Matt

[tunnelmike]

My 85 9.9 had a hourglass shaped carb throat while the 15 carb was straight thru. Did it make it a 15 ? Can't say. Was noticeably faster on the same 10' flat.

[Dd24skater]

Mine had a baffle in the center section that needed to be removed, and carb jets