Do the RPMs drop significantly when you pull the starter off or will it run strong at top end for a while? You might try a new glow plug on it just for kicks before you start diddling with your LSN. I'm with Perdo, if you left the plug in when you put it in the crockpot you might have done something to the element.
Was the engine running ok before you crockpotted it? If it was really dirty, even though the outside is clean now some of the trash that came off in the crockpot could be blocking something in the carb. I'd try a glow plug first, then adjust your needles..... if that doesn't do it, I'd back the needles all the way out and blow the carb out and see if that helps.