G' Day Larry,
That's the subpiston induction. It would have an affect on throttling but I doubt it would be that much or else Mills wouldn't have succeeded with their throttle design on this engine.
As far as I know engineering drawings of the Mills 1.3 throttle assy. are not in the public domain, so if you wanted to make your own you would need to borrow a unit and "reverse engineer" it as I did then grind the various form tools and make jigs and fixtures, buy a square stock collet etc.