I use the pinch test for low end only... and only as a last resort

Start engine, go to full throttle and adjust the high end by sound.

Then go to full idle. Let idle for a few seconds. If the idle slowly decreases, it's usually a sign that the low end is rich and therefore loading up as it sits there idling. If you go to WOT and it hesitates, again, this is a sign of a rich low end. If it quits when brought to WOT, it's probably lean on the low end.

When all else fails, I do the pinch test.

Bring it to idle and let it idle for a few seconds (Providing it will) then pinch the fuel line.

There should be a slight increase in RPM (Which you can hear) then the engine should quit.

If it quits right away without the RPM increase, it's lean. If the RPM slowly increase and and maintain for a few seconds before the engine dies, it's rich on the low end.