how does fuel cutoff work on the mac11?

[birdmanmt at juno.com]

I've heard it's a mechanical control on the board.  I've also heard that it can be raised/eliminated with a chip.  I purchased two chips, one for me and one for a friend, and both are supposed to have the qlcc code or some variation of it.  Neither seems to make any difference in the performance and both still have the cutoff at 1.6 bar.  Quite disappointing to say the least.  Anybody know for sure how it works?  

TIA
jeff redig