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Message: <blockquote data-quote="Tbarnby" data-source="post: 483507" data-attributes="member: 26035">2002 Mercury 9.9HP 4 Stroke to 15HP Carb ConversionI'm posting this, because I've never seen an adequate response on the Internet, and figure people may find it in a search.  OK, so, I replaced the carburetor with a 15 HP.  I ordered it from readysetboat, and received it quickly.  I originally ordered it from iboats, and after 2 weeks, they still had no ETA on shipment to their warehouse...so I canceled that order.  I replaced the carburetor (had to do some minor sanding on a brass fitting, for the choke to work).  I took the boat out, loaded as before, and got 21.1 MPH.  It easily gets to 5500 RPMs with the Lowe 1648 Big Jon, and 9" pitch prop.  Noticeable difference in the size of the Venturi between the 9.9HP and 15HP carburetors.  As the timing is the same on both engines, the exhaust parts are the same, and the displacement is the same,  I Figured this was all I had to do.  And that seems correct.  The performance increase is very noticeable, and the conversion is very easy, and made the boat much more functional.</blockquote>