9.9/15 hp mod

[badbrad1m]

Does anyone have the carb sizes (venturi size in mm) for the 9.9 and 15 hp Johnson/Evinrude? I am looking at a 1980 9.9 that the owner said the previous owner said (?) that it had been modded to a 15 hp with the carb. I also understand that the exhaust tubes need to be changed for this mod - is this correct? Thanks!

 

[iwombat]

Re: 9.9/15 hp mod

All that, and some years had a reed spacer and other differences as well. When people do the "mod" w/o making ALL the changes, they end up with a 8hp instead. Make sure you do the research for all the differences for your particular year before spending any $$.

 

[Rick.]

Re: 9.9/15 hp mod

Hi There. I copied this information published by the machinest. You can find it in the FAQ in iboats boating forms above. He has lots of great information available in his articles. Pictures too. Enjoy, Rick.

The outside visual dimensions of both carburetors appear the same, unless you look inside the throat. If you look in from the rear, you will have to position the throttle plate to a horizontal position to be able to see the throat very well. The 9.9 hp carburetor?s internal throat is .625 dia., 15 hp internal throat is .875 dia. up until late 1987 when they went to a plastic topped carburetor. The outlet or rear throat dia. is the same on both to match the manifold port dia. The idle jet venturi system is also slightly different between the two. The part number for the the pre 1987 9.9 hp Carburetor Assembly is #388936, while the 15 hp Carburetor Assembly is #338273. This increased throat dia. & larger main jet allowed it to breather better & pull more fuel in, increasing the RPM about 1000 RPM.


9.9 on left & 15 hp on right as viewed from front, & with choke open, notice the internal throat size differences 9.9 on right & 15 hp on left as viewed from rear, but with throttle plate closed & you can not tell any difference