I think now I know what I should do. I already started fixing the fuel tank issue making it not to vibrate and cause the "weak fuel supply".
The question now is should I increase the pressure from the mufller to the tank? The Bisson pitts has two tubes for outlets, is it wise to close the one? Will it affect in any way the engine performance?
I also intend to fly it the next time without the cowlling so that the will be more airflow to cool the engine. If everything ok I will be testing it this weekend.

Thanks for the help.