yes it (smaller intake) will restrict flow to the head even with the 24mm carb compared to using the ported one. think of the intake connection as a window between the head and the carb. You'll only be able to move so much mix at a certain rate through the opening. it's a mathematical situation with a pretty much fixed number. Open the window more (bigger intake cross section) and you can move more through. the carburetor can be adjusted, via jetting, and it responds to the air demand based on the vacuum pulse. The window can't be adjusted. of course there's a balance point between volume and velocity going in through the system.
Overall, these 150s are treated very simplistically for the average user. to really dial in any engine takes a good knowledge of intake to exhaust flow ratio and a means to make changes based on that knowledge and clear picture of where you want the power band and how to get it there. That's why Tom and others makes some $s doing what they do with the heads etc. They've spent the time to science it out and create proven combos. when the end user puts it all together, they still need a clear picture mentally of what they're assembling and how it all works as a whole.
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