That does sounds like your needles simply aren't right. I have that same engine and it's the most temperamental one I've ever owned. Suddenly dying is a classic lean condition at idle, so you have to open it up. The LSN affects the top end even at WOT on these engines, so if you get a decent idle setting but find the midrange is all wacky, it probably indicates that the needle combination is off. It's possible to be too rich on the top and lean it out on the bottom, or vice versa. That will let the engine run well at one throttle setting but no where else. With yours, I's suspect you're too lean on the bottom and too rich on the top.