THE BARREL ON A ROTARY BARREL CARB RAISES AND LOWERS AS THE THROTLE POSITIOIN IS CHANGE. ITS POSIBLE THAT REMOVING THE SPRING ALTERED THAT NEEDLE SETTING. COMPARE THE 2 CARBS TO SEE IF WHEN U ROTATE THE THROTLE ARM IF THE UP AND DOWN POSITION LOOK THE SAME ON BOTH? I WOULD BE INTERESTED TO KNOW WHAT RPM IT TURNS WITH A 18-6 AS MINE WAS 7400 STOCK AND I DIDNT TRY THE 16-6 BEFORE I MADE ALL THE MODIFICATION TO IT. IN MY THRUST TESTS THE 18-6 IS MUCH BETTER BUT FOR RPM THE 16-6 IS BETTER. REMEMBER RPMS ARE ONLY FOR GLORY THRUST IS WHAT KEEPS US OUT OF THE MUD. KEEP PLAYING THERE IS A LOT OF POTENIAL IN THAT MOTOR.
FARMER TED