My butterflies are solid pieces of brass. One closes tightly enough I can't blow thru it(with my hand cupped on the outlet), the other leaks just a little. I was thinking the piston springs might be a little weak, and the pistons don't close fast enough (once throttle is released, and butterflies close) but being a newbie to SU. maybe ATF is too viscous). I'm used to the near instant RPM drop when a Mikuni Slide closes...