RE: Evolution 61 Stalls going Vertical
John,
How far back is your plane's fuel-tank?
Some people incorrectly assume; that they can mount the tank at C/G and the engine will run... This would require a positive pressure, on-board fuel-pump.
The tank must be smack against the back-side of the firewall, for the engine to be able to run consistently both level and nose-up.
What did you change, if anything?