I put a perry pump on my moki 1.35 in a funtana 90 with a bisson pitts muffler due to this problem. It did instantly solve the problem and transitions as fast as you can move the throttle stick now. You can also put a check valve on the pressure line from the muffler to the tank so only pressure goes into the tank and does not escape, you just need to put a fuel T between the check valve and the tank with another line hanging with a plug in the end. This will allow you to release the pressure in the tank after flying and can be used as an overflow line as well. One other thing you can do is block off one of the down tubes on the muffler to create more back pressure, creating more pressure to the tank. Hope this helps