One thing that's confusing is where you say you have a blitz bov (blow off valve) and you turn it up? Do you mean you lessened the tension on the spring so it let air out easily? Or do you mean you have a boost controller and turned that up?
If you have the blow off valve, the problem is that. It's venting air to the atmosphere that the ECU thinks is going into the engine, and it is adding fuel to compensate... but since that air ISN'T in the engine, there is too much fuel, and it is flooding the engine, causing you to stall...
The best way to fix it is to go back to a recirculating bov as it was when it was standard, but then you lose the noise that comes with a bov.
Hope this helped a bit