My point was that you cannot assume anything.
The HS orifices are specific to both model AND carb. You cannot just put in the orifice that is spec'd for your model if it is not the carb spec'd for that model and be assured it will work.
As MTboatguy stated, you need to determine what carb you have first. You might try tracking the float chamber number to the OEM carb it was spec'd for. There is a "reverse lookup" app somewhere....can't remember the website. Maybe someone can weigh in. You could try working back from the float bowl part number and assembling a list of models....then do the same for the upper plastic cover. See if there are any common models.
There is also the good chance that it is a "Frankencarb" assembled from stuff that fits. Just because it bolts up doesn't mean it will work properly.
The orifices also are not interchangeable....as far as i know.
You can get a #50 in 8-32 external thread.....or 1/4-20....C and D type....and 5/16-24. It depends on the float chamber.
That is why the orifice can change a few times for the same HP over a few years...even though the basic design doesn't....the carb does, and all bets are off.
So you absolutely need to use a part number....NOT a "#50" designation. That just indicates the ID in thousand of an inch....not compatibility.
I have a fairly complete chart of OMC orifices....the part number spec'd for your motor is a 323708....its size is 8-32 x 0.050.
Bottom line, unless you can find what that carb was intended for and if it was used on a 9.9 you might be able to use the orifice spec'd for that year.....but maybe not.
I also do not think that 5000 in a barrel is a good benchmark....if you can do that on a boat, then you may be getting max performance already. Only option beyond that would be re-propping.
