Hi!
Well if you have problem with your present tank why not get a Tettra "bubbleless tank" from Dave Shadel (US YS importer)
These Tettra tanks are used by every pylonracer in the world and give much better reliability than ordinary Du-Bro or Sullivan fueltanks.
Tank size is vital...240cc -300cc (8-10oz) is what you should use. Not bigger!
Always mount the tank so the centerline is horizontal with the carb needle.
Use as short fuellines as possibly!
Plug: OS 8 or Enya 3, and never ever reuse an old glowplug washer!
Always put in a new washer when you change glowplug.
Never use more than 15% nitro!
Also check all bolts and retighten if necessary.
Prop is also vital...APC is what I recommend, size is up to you. Anything from a 8x6 to a 12,25x3,75, will work depending on the airplane.
Most of the time a 10x7or a 11x6 will work best in ordinary sportairplanes (if you fly at sea level).
Never use a cheap plastic spinner!
Always balance your props and balance them by sanding on the heavy blade (on the front sidewith the airfoilshape).
You could also paint the tips white if that helps balancing (it also helps visibilitiy).

Regards!
Jan K
Sweden