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  Will Evinrude 40hp convert to 50hp?

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Author Topic:   Will Evinrude 40hp convert to 50hp?
skookum point posted 01-23-2001 02:56 PM ET (US)   Profile for skookum point   Send Email to skookum point  
I'm the proud new owner of a really fine Whaler 15 SS. It is powered by a 1987 Evinrude 40 which will provide adequate power for my sea-level exploits. However, I will sometimes be running the boat in mountain lakes and want to compensate for the power loss experienced at high altitudes - 5,000 to 6,000 ft. I'm thinking a 40hp is going to act like a 30hp in the thin air.

Anyway, somewhere on this (excellent) site someone mentioned that a carburation change would convert a 40 into a 50. I think the bore and stroke on the 40 is identical to the 50. Does anyone know if this is practical, what the cost might be, and whether it can be done by a shade-tree mechanic?

FISHNFF posted 01-24-2001 04:19 AM ET (US)     Profile for FISHNFF  Send Email to FISHNFF     
I had my 40 Yamaha converted to a 50 by changing carb jets, reed valves, and exhaust manifold (40/50 same block). I believe our 40 OMC came as a 40/50/55/60. I would guess the same modificatons would work. Check with your OMC mechanic if they are still around.
whalernut posted 01-24-2001 05:12 AM ET (US)     Profile for whalernut  Send Email to whalernut     
FISHNFF, acctually I believe for some time now, including the present the OMC 60-70 2-stroke outboard motor are the same except for the carburation. Regards-Jack Graner.
Easy E posted 01-24-2001 02:24 PM ET (US)     Profile for Easy E    
A friend of mine has a 17' banana boat type with a 40hp Evinrude that he had a mechanic change to a 55hp.Im sure all he had to do was change the carburator i think there is two at about $130 a piece.I dount no about exaust manifoils and all that,perhaps yamahas are different.Im pretty sure omc made 40,48,50,55 all on the same engine block.I dount think the 55hp carb can handle oil injection so if you have one of them oil injectors you would have to go with a 50hp carb.The 55hp carb is for premix only.Well good luck...I know it can be done-Easy E
Clark Roberts posted 01-24-2001 06:14 PM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
A check of part numbers on the various blocks will indicate if blocks are identical!
Some engines are derivatives of same block but have different porting (intake and exhaust) to help achive additional hp.. if part nos. are different that inticates that the porting may be different and,if so, no amount of fiddling with carbs (you need carbs with bigger venturis, not just bigger jets) and reeds will get the additional hp you desire..
Milling the head to raise compression is not recommended as you will most likely hole a piston first time out! Guess my message here is that just because displacement (bore and stroke) are same doesn't mean that blocks are identical... be careful and get some good local professional advise... then go for it!!!! Clark .. The old Man and the Sea
FISHNFF posted 01-24-2001 07:42 PM ET (US)     Profile for FISHNFF  Send Email to FISHNFF     
Whalernut. You are right on the newer models, but I believe at one point, late 70's-early 80's OMC did have a 60HP 2 cylinder. Later they went 3 cylinder 60.
sport15er posted 01-24-2001 09:24 PM ET (US)     Profile for sport15er  Send Email to sport15er     
True Fishnff, I have an '87 Evinrude 60HP, 3 cylinder.
skookum point posted 01-25-2001 02:56 PM ET (US)     Profile for skookum point  Send Email to skookum point     
Thanks for the feedback, whaler boys! All very helpful advice. I'll look for an experienced OMC mechanic and go from there.

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