ORIGINAL: chemie
At 1/2 tank, it was fine at low throttle but cut out on high when pointing down. However, it cut out after a much longer period. Ran maybe 5 seconds, slowed, then got fast, then died. I pulled out a 51 size engine and it did the same thing but ran for 10 seconds. I guess the fuel usage explains that. The 51 runs at any tank level and any orientation in the sky so I think this ST90 should be OK too. Now time to maiden and find out....
We often talk about "pointing the nose down" but often no one explains to what degree it is pointed down.
If you point the nose straight down, you may expose the clunk almost instantly if the tank is not absolutely full.
When I test "nose down", I angle the plane about 30 degrees or less, nose down, to try to keep the clunk in fuel.
If you've angled the plane more than that, then things sound pretty normal.
In the air, you'll hardly ever have the engine running full throttle nose down for more than a half second.