Just wondering if the combination of slowly closing the throttle and pushing the nose over causes the fuel to move to the front of the tank, but there's still enough throttle up to run out what's left in the lines.. Chopping it back to idle before pushing the nose over could reduce the fuel demand and mask the issue? A hopper tank might help IF this is the problem.

I've never seen a clunk that will fall to the front of a tank, but most of the time my nose is pointing down, I'm well off the throttle and have really long fuel lines (tank over COG).

YS sell a foam clunk for their DZ fourstrokes as little bubbles play havock with the positive displacement pump arrangement in their injected motors. The foam cluck keeps out the air and acts like a mini fuel cell when the cluck is exposed..