Like you said, all the ports on the sleeve will close before the exhaust, any ''possible'' added pressure will make its way out of the exhaust...
No matter what kind of pressure you can add, it will go out of the exhaust....
I also dont see the need of adding pressure to the tank, unless your tuned pipe is not restrictive enought... You can tune the engine so rich that it will flood anyway
Its like blowing compressed air into the venturi while the engine is running, it act like it boost the power, but its only leaning the mixture and the rpm will change...
