Well, there wasn't any gum or residue. I had cleaned the needle with a squirt of carb cleaner like I always do, and lubed the interior of the carb with WD-40 like I always do. The actual rubber tip itself was deteriorated and sticky/gummy, and I failed to notice it. It really only showed up with a magnified examination and by poking at the rubber. You could poke it with a tooth pick or a probe, and it was just, well, "gummy"; soft and sticky. My first clue to the problem should have been when I removed the rubber fuel hose and it had "glued" itself to the fitting, literally....

I ran into a similar problem a few years ago investigating and repairing an ultralight airplane crash. The engine quit on take off and the resultant hard landing did quite a bit of damage. What I finally found was that all the ignition system wires that were bundled/tywrapped on the engine near the carb area had mushy insulation. You could squeeze the insulation and it would compress and come off in your hand, feeling all sticky and gummy. The tip of this needle valve in question was kind of like that.

AV8TOR