John, not many engines will run on Diesel fuel without changing the head, a few will though. I have an OS LA .46 that I bolted a Davis Diesel head on to without breaking it in first on glow. Mr. Davis recommended breaking converted engines in on glow first. My Saito .80, (15.5 to 1 compression ratio) will fire up and run on Davis fuel with the coil removed from the plug. It will turn a Bolly 13.5x8 at 8,760 rpm and idle below 1.400 rpm.
Bob, it sounds like the .91 is in good shape and timed correctly. My guess is that the LS needle is too rich. I'd personally would screw it in until the engine hesitates when opening the throttle then back it out 1/8th to 1/4 turn, you should find the sweet spot close to that setting. Let us know how it goes, Thanks, Dave