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Author	Topic:   2004 Yamaha 40 - Change Jets?
skred	posted 07-21-2009 04:16 PM ET (US)         A "knowledgeable" friend told me that the 2004 3-cyl 2-stroke Yamaha engine could be upped to a 50 by simply changing the carburetor jets... I'm affectionately suspicious....
Tohsgib	posted 07-22-2009 03:30 PM ET (US)             As you should be. If it were that easy everyone would do it. First you have to check that carb part numbers are the same. If so then check jet numbers and go from there. Usually it also has to do with advancing the timing and maybe larger ports. A 25% increase in power is not going to happen with a jet change.
skred	posted 07-22-2009 05:19 PM ET (US)             Thanks Big.... I found some old posts and it looks like there's jets, reeds, port size, and exhaust considerations - depending on year and model. Ah, well, I should be happy with 30+ mph anyway....

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