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PostPosted: 05 Aug 2016, 12:53 

Joined: 02 Mar 2015, 14:19
Posts: 1
I have a Yamaha 1997 40/28 jet drive outboard model 40EJRV. This is the same motor used in the 50 HP 50EJRV. All the part numbers are the same between the two for carburetors, jets, reed valves, intake, pistons, crank, engine block, head, electronic CDI ignition. What is used to add 10 HP and between the two motors?


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PostPosted: 05 Aug 2016, 14:41 

Joined: 02 Mar 2012, 02:24
Posts: 94
Location: St Louis, Mo
I've done this to a 1988, gained about 400rpm. The part diagrams on boats.net are a bit confusing but the carbs on the 40 are smaller and the exhaust tube used on the 40 is really restricted. Yamaha built the 50 and then de-tuned it to market the 40, you'll know what I mean when you see the restriction added to the exhaust tube.

Not great pics but you get an idea of the relative sizes of the venturi.


tb yam50.jpg
tb yam40.jpg
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