I have posted this on the S-D side a few times, but realized it may also help find boost leaks on the SCd Yamaha skis too. The link below shows a product that you can clamp on the front/inlet of the SC, clamp it tight, then use the Schrader/tire valve to put air into your SC/IC/TB. Usually at around 5+ psi you will very quickly hear air hissing out if you have a leak. You can also spray soapy water on the SC to IC to TB tubing too, and the bubbling will also show if/where you have boost leaks.

It is cheap and easy, and guarantees that all the boost you are making is getting into the motor.