Beast.....
I have run With and Without a fuel filter and I have notied NOchange in performance, for better of worse.
An external filter is just an added level of protection against sucking debris into your engine.
I would get a new Tank.
It ISpossible to have a leaking pickup INSIDEthe tank.
A new tank is less than $10. I would also replace the Fuel Line as well.

Also.....have you Sealed your Engine with Silicone, to prevent air leaks at the Engine and Carb?
Checked to make sure all the Engine/Carb screws are Tight, and Exhaust couplings are air tight?