Curt,
Actually, I use my own spreadsheet for fuel mix calculations. The numbers work out to 22.82% lube (about 49.49% syn. 51.51% castor) the nitro percentage drops from 10% to 9.41% and methonal is 67.76%. The lube content may be a little high, but it's been a good all around mix for my ABC, ABN, or AAC motors.
I don't believe backplate screws or head screws are loose or leaking, but , I haven't checked them. Yes, the spraybar goes through the venturi, it's not a sprinkler type.
I can try changing the plug and reducing lube content, but it has to wait until I have something to test it on. The profile it was mounted in is a little bent because of structural failure caused by exceeding the decelaration design limitations. An unfortunate result of a flame out!