How to Confirm 9.9 was "Converted" to 15hp.

How does one confirm that a 9.9hp 2-stroke was "converted" to a 15hp. I'll be looking at a used one tomorrow. The owner believes the carberator was replaced with a 15hp. Does exhaust need to be changed as well? I don't know what year it is, but photo is below.

Compare the part number differences for the 9.9 and the 15 HP models. To determine which 15 parts needed to be installed on the 9.9 to increase its HP to 15. Then inspect the motor to verify that the parts have been installed.

boscoe said:

Compare the part number differences for the 9.9 and the 15 HP models. To determine which 15 parts needed to be installed on the 9.9 to increase its HP to 15. Then inspect the motor to verify that the parts have been installed.

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You don't seem to understand that the point is to verify before purchasing the motor. If someone says they're selling a motor that has been upgraded, how is one to know before purchasing that the carb has been replaced, etc.

I think that I do understand the point. Actually, I know precisely. This is not my first rodeo. Makes perfect sense to know what one is buying before one buys it. However all too many do not.

If you are looking at the motor then I suspect that you will want to visually inspect it. Also, inspect the documents that prove when and where the 15 HP parts were purchased. Documents that might indicate when the mechanic did the modification. What he did.
In some cases it is easy to verify a modification. In other cases, not so much.

Since Yamaha has offered a 9.9 HP two stroke and a 15 HP two stroke since 1984 through 2009, and you don't even say what year we are talking about, I am unable to proceed further.

If the seller can provide the model identity, or better yet the complete engine ID, then we will know when it was made.

Looking at a number of 9.9s and 15's, over several model years, it looks like the difference is the reed valve assembly.

To confirm that a 9.9 has been converted to a 15, the carburetor will need to be removed to gain access to the reed valve assembly. So as to confirm that the motor has really been modified.

boscoe said:

Looking at a number of 9.9s and 15's, over several model years, it looks like the difference is the reed valve assembly.

To confirm that a 9.9 has been converted to a 15, the carburetor will need to be removed to gain access to the reed valve assembly. So as to confirm that the motor has really been modified.

Click to expand...

Thanks. I ended up buying a 9.9 4-stroke with no claims of being modified.