".... I also restricted the air cleaner intake a tad, using a piece of pvc tube which is about 1.6mm thick, with the intent being that more suction may be (or maybe not

) on the hose from the rocker cover....."
This is somewhat counterintuitive... Pretty much all tuning mods involve opening up the air intake capacity of the engine... which then allows the addition of more fuel to produce more power. I've never seen anyone advocating reducing the air intake.
Even if your restricted flow into the carb was balanced by the air being "sucked" into the filter case via the breather crankcase, you're substituting clean colder air with hot dirty oily air... Can't be good.
Cheers, Ian