Fuel Flow questions/PROBLEM

[little rocket]

Ok
I installed a check valve in the return line and started engine then shut fuel valve off to verify that the check valve was working and after a few minutes the engine quit from fuel starvation ,so the check valve is working .
BUT the problem of running rough and pushing fuel out the carb overflow is still happening .
I put the carb mate on and the carbs are in balance at an idle and at 3000 RPM but still runs rough and pushes fuel out the vent tubes.I just did the prop balance 2 days ago. Also checked balance tube ,even made a different one to see if that made a difference,it didn't. Engine has 600 hours.
I hear everything you guys are saying ,BUT the fact that with NO check valve and the fuel valve shut off it purrs like a kitten in all RPM ranges.So the only fuel it is getting is from gravity feed from the UNCHECKED return line.
With the fuel valve off there is NO fuel flowing to the electric pump or to the gaslater or the mechanical pump.
With that system/fuel valve turned on it runs like crap both without the check valve and with the check valve.
I tried shutting the electric pump off and just using the mechanical pump but same crappy running engine.
It doesn't overflow the carbs at higher RPM but when you throttle back it starts overflowing the carbs again .
But with NO check valve and the the fuel shut off so it can only get the fuel from the unchecked return line threw gravity none off the above problems are present.
Seems to indicate that it is getting to much fuel and can't get rid of the excess threw the return line.
Where are guys tying into the fuel system for your fuel return line?
THANKS