G'day Mate,
My advise is use an 11x6 prop, & balance it properly, tune your motor rich enough so that when you raise the nose of the plane at full throttle, it increases revs slightly, then it is rich enough to fly, without cooking plugs, & overheating.
Forget tacho tuning, use your ears, conditions change, tach readings don't, sometimes you can run a motor leaner, other times you need it richer, depending on the weather conditions at the time.
Use an OS #8 plug, & see the difference, when tuned correctly.
Also you must have an air leak in your tank, or you would not get bubbles in your fuel line, this makes it even more important to get your tuning right.