Thanks for 'confessin' to swipin' my idea. I know it's in here somewhere, another thread, another day.
The idea is a way to imitate the angles of the forces on the fuel in flight. We have gravity and centrifugal force. CF is usually 3 or more times as much as gravity. Both forces act at right angles (within a skeeter's whisker) to the long axis of the fuselage - say through the engine shaft?
Start the engine. Hold the fuselage centerline horizontal through all of the following.
Turn the wing leadouts straight up and set a comfortable RPM so you can hear if it leans or riches out in the next moves. Bill mentioned resting the outboard wingtip on your foot. Two reasons: Keeps the ground/tarmac from scuffing your wingtip, and gives another point 'hoding' the model. The wings vertical position is basically a resting place while you think about what you're doing.
We don't need to duplicate the exact angles of the CF plus Gravity 'resolved' force. Any angle that we can pretty much repeat, large enough to cause an RPM change if the tank isn't right, is good.
The angle is in ROLL attitude, not nose up or down!
Once you got it running, comfortable, and you've settled down, ROLL the model (fuse centerline horizontal) to about 45° 'cockpit UP' and tach or listen close to the engine.
Then, ROLL the model (fuselage centerline still horizontal) to about 45° 'cockpit DOWN', and tach or listen close, again.
If there's much difference between the two rolled positions, do it again until you are sure which atttitude makes it go richer (or leaner, just be confident you've got it nailed.)
Shut the engine off: Nose down, other wingtip up, and a finger over the uniflow vent tube is about quickest and safest.
The engine went richer to the side that the tank was "too high" in the rolled position. Lower it some. (If you judged by leaner, then the tank was too LOW in the rolled position where it leaned out. So, you'd raise it some.)
Adjust the tank height, and try it again. Going through the wig-wag and shut off a few times should get you to where there's no audible RPM difference between the rolled 45° positions, and very little RPM difference on a tach.
At least, before a first flight, this should put you close enough that the engine won't flame out on you because of tank height problems. For me, most often, little to no further tank height adjustment will be needed for even run both ways.