First, make sure you've got spark at that cylinder. If you do and your getting the plug wet then that same plug is working it another cyl when you swap it, it's not fouled and I doubt the needle and seat are flooding it out. Possible, but slim I'd say.
Is the pipe not getting warm with it only at an idle, or varied rpms for a few min?
I'm guessing you've got a clogged pilot or something in that circuit, assuming again it's got spark.
What did you do to clean the carb? Spray can of carb cleaner is not thorough. To do it right, go to auto zone or somewhere similar and get a gallon pail of barrymens chem-dip. Strip the carb completely down, remove all the jets, air screws, etc and dip it over night. THEN use the spray can of carb cleaner and shoot it through all the passages as well as each jet. You'll have wanted to dip the main and the pilot also btw. After that follow up with compressed air in all the same places and reassemble. If you want to be anal hit the carb with WD-40 when it's all together to make it look pretty.
The slime you said you found is fuel stabilizer I'm guessing. If it's been put in the tank at too high of a ratio stored, it'll make a real mess.
My .02 on what you posted up...
