The H9 Twist planes are great flyers.

Instead of doing the tilt test at idle . . . . Tune your top end properly and do your tilt test. If the engine speeds up a little on the tilt test it is OK. --- Then tune your idle with the air bleed screw. Tune the engine for best idle . . . . Then check your transition back to high speed. If the engine immediately quits, the idle is too lean. If the engine stubles along for a while and eventually picks up and runs correctly, the idle is rich.

"Rich in fuel"

On most air bleed carburetors, the idle mixture circuit only works at a very low speed. It has no effect at higher speeds. The air bleed hole is covered up by the throttle barrel at greater openings than idle..

You should be able to get the engine to idle in the 2,000 - 3,000 range.