If everthing else is correct, float level, air tight, idle set correctly, stock needle on middle clip.
Slap in a #300, if it babbles its brains out, come back in sizes until it gets onto the powerband and pulls hard, otherwise leave it alone.
A #300 is not going to kill it.
Take a handfull of jets and plugs to where you can find a long enough place to get the WOT and do aproper plug chop.