I have a 160 FX , Perry pump, slimline pitts muffler. Low end and top end seem to be in the ballpark but I can't seem to tune out a midrange burble. Tried going from a #8 to a #4 plug...nothing. Tried switching from 15% Coolpower to 10% Omega.... nothing. Tried leaning the pump....nothing. Any insight would be appreciated.

If the engine runs well at the top and bottom, and will accelerate well, even if it's been running in the midrange for a bit, we'd not worry about it. Model engines do not have linear response on their carburetors, and they all tend to be a bit rich in the midrange. If the engine's running well, we'd ignore richness in the midrange.