carb heat, LOP, etc.
Yeah, I don't actually RUN at 100 LOP - what I meant was that it WOULD run there as opposed to rough-run. 30-50 (the cylinders aren't perfectly matched in a carb engine) is what I try for.
Carb heat WILL richen, but that's not the point. Carb heat warms the fuel-air mix and helps to facilitate even distribution, therefore more even CHT/EGT.
Another thing is part-throttle. This angles the carb butterfly and can sometimes increase downstream turbulence in the intake. More turbulence (to some degree) will also enhance fuel-air mixing, and consequently promote even burning.
YMMV of course.
My 7.5gph and 165ktas are typical at 6000-9000 feet, depending on temperature. Last week I made a trip with light winds and got nearly the same exact numbers from 9,500 all the way to 15,500. Amazingly consistent. I don't have a lot of experience at high levels yet to say whether this is repeatable. BTW - this is with a very heavy ship. Mine is fully insulated and carpeted, rear hatshelf compartment, two-axis autopilot, 2-part epoxy painted inside and out, full-IFR, oversize tires, and with nearly 100 pounds of baggage. Flying weight was probably close to 1800 pounds. I can usually get about 170+ktas at 7.5-8gph when I'm traveling lighter, just me and half tanks. It's a quick ship, John Hughes did a great job.
G.