Converting a 2000 Johnson 6hp to a 8hp

[joeall]

I'm considering converting my 6hp to an 8hp. It appears that the only difference is the high speed orifice . According to the parts diagram the 6hp uses a No. 37 orifice and the 8hp uses a No. 36 orifice. This does not make sense to me that a 6hp orifice is larger than the 8hp. Does anyone has any experience with this issue?
Thanks

 

[racerone]

Carburetor part # is different.-----Engine block shows a different part #

 

[joeall]

Thanks! You are correct, the carbs and engine part #s are different, I compared thirteen major engine parts (pistons, mainfolds etc.) for the 6hp and 8hp and they are identical except the carburetors. I compared the significant parts for the two carburetors and found only two diferences, the high speed orifice and the metal links that connect the high speed butterfly to the cam roller.
My conclusion is that the high speed orifice and carburetor link must have an impact on RPMs . If anyone has another explanation please share it.
Thanks