My 340 getting 6 mpg

I agree completely about taking a look at the air bleeds first. For me though, I would be too chicken to change them out unless I could stuff a blue towel into the bores before pulling the bleed out to make sure it does not accidently drop into the butterflies... then I somehow jerk the throttle and let it through. Ugh!
Yup! Im in that group!

Me, I'm taking the carb off to do any work like that.

Paid way too much for the motor to risk something falling into it without me noticing and then ruin it for the sake of removing 4 nuts and some linkage.