Re: Mercury 7.5 vs 9.8
I believe that you are right. Most motors today have other differences to get different horsepower from the same powerhead, but I believe that the 7.5/9.8 is one of those where the only difference is the carb.
It won't be a simple jetting issue. The throat of the 9.8 carb may be a tad larger, or the venturi isn't quite as small as that of the 7.5. Make sure that the boat is rated for the 9.8 if you do the modification (hard to imagine a boat that wouldn't be), and if you ever sell it, put the 7.5 carb back on. You can include the 9.8 carb if you wish, but to prevent possible liability issues, never sell a motor whose horsepower isn't as is indicated on the hood. If the buyer wants to make that modification himself, that's his risk. Better yet, get a 9.8 hood and skirt when you get the 9.8 carb. Always appropriately represent the horsepower of the motor and it can't come back to haunt you should an accident happen.
