Hi Fernando, Sounds like you may have a possible fuel flow restriction? or air entering fuel system? Be sure that you install wire twist tie wraps around all fuel tube fitting connections. Replace those plastic tie wraps on your fuel tank as they can also let air in and are not recommended, Check that your fuel breather line has no restrictions or kinks, Check that your fuel tank clunk pickup has no restrictions also. Felt clunks are not ideal as they can cause fuel flow restrictions also. Check your fuel pumps flow rate also. It does sound like something straight forward is causing the problem so just going through the process of elimination for now.... Please let us know how you go

Cheers- Marty