The restricted fuel-flow argument seems to be gaining following around here.

The two GMS 47s in our club both suffer from a tendancy to flame-out when the planes they're in are placed in a dive steep enough to cause the revs to rise by 20% or so. It's as if they just can't suck enough fuel to sustain those revs even though they're tuned slightly rich of optimium at full-throttle.

(no, it's not a clunk or fuel-line problem, you can hold the planes at the same or even steeper nose-down angle on the ground and the engine runs just fine).

We drilled out the exhaust pressure-tap nipple and that helped a little (the engine on one plane now picks up after appearing to die during a bit of a dive).

One can't help but get the impression that these engines might be just a little over-carbureted too.