3 quick things about this engine/carb:

A: make sure yout throttle barrel isn't moving side-to-side (side play) during flight. I have found that if it moves, especially during a near idle position, it can cause the engine to cut out. This might be happening during your maneuver. Making sure the linkage puts a gentle side pressure helps with consistancy, at least on these Evo carbs.

B: Back pressure. This engine (and the 1.00, too) is especially sensitive to muffler pressure, and IF you have an aftermarket muffler you will have to reduce the outlet area. This will help make your low end rock solid, along with A and C.

C: This may sound crazy, but bear with me- I have fiddled with several of these Evo 60's for a long time. Hook up a temporary on board glow, and see if it fixes the problem. I have found difficulty in getting the 60NT to run well CONSISTANTLY when mounted inverted, especially at low throttle conditions. I know, I know, most two strokes are a bit more irritating when inverted. However, I have had many success stories with inverted mountings, but this engine is different in some mysterious way. Lean or rich, it didn't matter. Tank position was good, with nice & short tubing. This is my theory and opinion, but I think there is a connection with this and the glow plug position in the head (evolutions are canted towards the back somewhat) and poor reliability in some attitudes and throttle settings... maybe fuel droplets in the intake charge... heck, I don't know. You may try to verify this by doing some other negative G maneuvers at low throttle or idle and see if it does the same thing. I could adjust the engine to a perfect low & high mixture when sideways or upright, then turn it over and it wouldn't idle well and the problems would start. Different brand 60 did not have the slightest problem with the same plug. I know your engine is upright, but perhaps your negative G maneuver is bringing out this trait in your situation? Just a guess, but I will bet a 6 pack on it- IF your plumbing is right!

I put an on-board glow on this engine and the problem of quitting stopped, and the engine ran like a scalded dog inverted. I later repositioned to a side mounted engine configuration and took off the on board glow with success as well. Runs awesome to this day!

Just my observations, folks! Don't flame me! [8D] I still do love all of my Evilution engines! They pull hard.

EDIT: others have mentioned the fuel tank level(a plumbing item)... I second those observations also.