Stock Prop to 9/15 Hooker Same Max RPM

I have a 93 b1 that is mostly stock with a Riva red pipe. I bought a tach for tuning and noticed that the max rpm I could get out of it was 6690RPM. I read that the Riva likes more rpm so I decided to swap to the 9/15 hooker because it gets such good reviews. The 9/15 is a big improvement with the bottom end power and hookup but I was surprised to see that my ski still wont rev past 6690. It does not feel like its hitting a rev limiter, it just wont rev anymore. I believe that the stock 61x limiter is at 7100 anyway. Am I missing something obvious here? Is the limiter just that subtle?
 
I should have mentioned that I installed a stubby cone along with the impeller. It just seems really add that it would turn the exact same rpm on full throttle run that it did with the stock impeller. It makes me think that something else is limiting it. I am going to check compression today.
 
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Your peak rpm is limited by the stock 61x cylinder, the exhaust port is too small. Plus the full throttle mixture (top screw) may be a little rich. A little port work or a 62T cyl leaned to peak will turn 6900+.
 
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