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Difference between 7.5 and 8hp motor, 1983 Johnson. Also, possible to convert to higher hp?

redfishsc

Contributing Member
I have a really good, clean 7.5hp available to me for around $400. I really think I need something in the 8-10hp range at least to get this 14' Starcraft SS aluminum up on plane, but this motor is a reasonably good price and well cared for.


What is the difference between this and the 8hp? The serial number is the same sequence for an 8hp. Is this just a re-labeled 8hp to eek it in under some "8hp restriction"?


Also, finally, is there a feasible way to convert this to something more powerful, like perhaps swapping the main jet or whole carb etc? This has the older metal style carb that should be much more durable than the 1986 6hp that I have that has that #$%@#$% plastic top.
 
The 8 hp had a 3 petal reed valve ( more air flow ) and a water cooled outer exhaust cover.-------------There is not much that can be done to that block to get more power than 8 hp.
 
OK, thanks for the info. I'm not surprised that an upgrade in output isn't going to happen. I will hold out for a 15hp.

Now, can anyone explain to me the difference between this and an 8hp?

You might be able to get it on a plane with the 7.5 with just you and a small fuel tank and your less than 120 lbs.

Lol, I haven't weighed 120 pounds since I was in 6th grade.
 
Can anyone comment on the difference between the 7.5 and 8hp? Is it just a relabeled version of the same motor (ie, different cowl), as it appears to be?


hold out for a 18 or 20. 25 is best :)
dino

I would not put anything over 15hp on my Starcraft 14'. I think it was rated for a 20hp max, but a 20hp is quite heavy (over 100lbs usually). My current motor weighs 50lbs and I don't want to go much more than about 75lbs.
 
It was mentioned before that the 8 HP version has more reed valve petals for better breathing !!----More to it than the sticker !
 
I would not put anything over 15hp on my Starcraft 14'. I think it was rated for a 20hp max, but a 20hp is quite heavy (over 100lbs usually). My current motor weighs 50lbs and I don't want to go much more than about 75lbs.[/QUOTE]

most 9.9 and 15 are the same weight. the best is the 1993 or newer, 256CC, Evinrude/Johnson 2-stroke at 72LBS.
lproduction stopped 1999 or 2000 but they sold the johnsons until about 2006. ( left overs ).

I agree 15 is plenty for my 14R sea Nymph. too. Rated for 20. But when my boat was made..they didnt know a 20 HP 4 Stroke would weigh 170LBS.
 
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