What can you do with a 7.5 merc.

[woodman]

I got a 20-25yr. old 7.5 merc from an 80yr. old guy who used it 2-3times.
It is pristine ,like new, the prop has orig. paint and it runs real sweet.
Is it worth mesing with to get more hp. for an 8' hydro?
What can be done to the motor?
Don't laugh I'm the Rookie that posted the thread in the Rookie Lounge.
I know it is no way a racing cantidate but ............?

[David_L6]

Is it worth mesing with to get more hp.

Short answer - No.

If you were able to double the horsepower (very doubtful) you'd only have 15 hp. A 20% increase in hp would be only 9 hp if you really have 7.5 hp to start with. Better to sell that motor and buy a bigger one.

[Richard K.C. Mo.]

Boat that size?

Sounds like woodman should check out the novice rules in NBRA, club foot and small boat n' all.
RichardKCMo

[krazy karl]

That is actually a pretty nice motor, one of Mercury's best selling at the time. Mercury underrated their motors back then, it will actually put out about 10 crankshaft rated hp, however there isn't much that can be done to this motor to increase output.
kk

[Bill Huson]

hmm . . .

not sure what model that 7.5 merc is, but you might want to check the actual displacement. Back in the `50s I had a Merc 10hp "Hurricane" ? It was almost 20 cubes, same as the Mk 25 I replaced it with. I'd fiddled a filed on the 10 but didn't change the carb, which I think was the main power restrictor. Sold the 10 to a racer who mounted the powerhead on a quicksilver unit (and probably changed the carb) and ran it in BU. My brand spanky new Mk 25 was only a few mph faster than the old 10.

Who knows, that 7.5 might be a 10 or 15 in disguise!

[Don]

the 80's 7 1/2 was about the same as the 9.8 version,the only diff was the carb.

[14-H]

9.8 vs. 7.5

I think the 9.8 had bigger ports. But they were definitely the same block and everything else was the same.

Put the powerhead on an old 25SS lower unit and this is still a legal J engine. FYI.