Hi!
Agree with Fencemagnet...the way you take pressure on the exhaust stubb area on the silencer is no good...much better to drill a hole and tap and place the nipple on the muffler...that way you get more even pressure. If you need pressure at all ofcourse..tha's not needed on engines like yours which put out low power and have small carb intake area.

Your drawing showing the tank set up is OK..It's what the Cl-guys call a "Uniflow" tank set-up and that's the best tank set-up you can have if you use an ordinary R/C fueltank. As I said earlier the Tettra "bubbleless" tank is even superior to the Uniflow tank though.
Regards!
Jan K
Sweden