Accelerating for a short burst, then cutting out when you apply full throttle is a lean bog.....the engine isn't getting enough fuel to feed it properly at full throttle. Richen your high speed needle a quarter of a turn. If it still does it, richen it another quarter turn.
Once it's very rich, and blubbery at full throttle, start leaning it out 1 hour at a time until the performance is good, but it's not lean bogging.
That "smell of melted plastic" was your engine getting extremely hot from running too lean.....good way to destroy it in a hurry.....