hello friends , i have the pleasure to say that i solved the issue with sniper efi and now it works as should be ! 
Part of problem was fuel filter and pump . First filter was a generic modern steel one , same as provided with holley basic kit . This was my thought , but i was wrong . We don't have any specs about micron filtration ; this make pump works bad , cause heat and probably high idle or surging . 
As fuel pump was already 60 psi as requested from holley , i have thought i don't need any pressure regulator as efi has return line pressure regulated . 
Well , i decided to put an eye on this when someone told me " filters can be too much obstructive , depends on micron , 10/20/40....100 and so on ." 
This never be so true . I moved from pre- pump  filter to past pump filter with pre-set 60 psi regulator internal , and return line all in one canister . 
Take few hours to change configuration and close the return line from efi . 
Start and ... wow  it works silent ... no more pump noisy , no more heat , fixed pressure steady , correct idle and most of all rpm drops as should do . Also this problem i think is referred to previous set up . 
I'm happy now .... just a week ago i was ready to get rid of this , but now , seeing the positive behaviour , i think this could be the end of carburator .  right to say i love carby , but riding an efi is really satisfying . 
What i learn from this story : yes efi can be really a source of problem and puzzling so much .
efi instruction is paired to nothing , it's on your own find  the right path ( there is a ton of info out there )
More electronic you add , more is difficult to have an easy set up . Need to be electronic or programming guy to know what you are touching inside ecu . Who like me is totally blind on this , better stay on coil set up .
A lot of people refers to RFI issue , but i don't think this is really the focus . once you have correct spark plug and wires i haven't found  problem with rfi . 
Wanna thanks everyone has joined this discussion  / problem solver . 
Alex italy .