Check the hoses as said, you want to be looking at the one which comes from the compressor housing to the Amal and the one from here to the actuator, if one of them has fell or or split you will run more boost, there is no point just upping the boost by itself, it's also very dangerous to do so, at 7000 RPM or 13PSI of boost on the standard software fuel injection is cut totally (Hard cut) which sounds like what you are experiencing.

Also the said fuel filter should be changed as this IS a servicable item regardless of the car.

You can connect a boost gauge to the plenum, but it's best not to tee into the MAP sensor or the fuel pressure regulator vaccum pipe.

Martin