Have you tried the "pinch test" with progressively slower idle speeds? Start at whatever idle speed you can get, then pinch off the fuel line as close to the nipple on the carb. You should hear the idle speed increase slightly, then begin to drop off. If it drops immediately, you are too lean. If the idle speed takes a long time to rise, you are too rich.

Don't bother trying this at a high throttle setting because the engine will be drawing too much fuel for you to hear any increase in speed before it dies. The idea behind this test is similar to when we ran control line planes without a throttle. The engine rpm would always rise as the plane ran out of fuel because the mixture got leaner.