Here is an excellent page to read about the MPS: The D-Jet Manifold Pressure Sensor by Paul Anders

This is by far the best info ever written about it. There is several pages of info on the other parts of D-Jet, but the MPS is the major part. The MPS has 3 adjustments:
1. is the full load stop, it's actually the big plug that is covered with epoxy.
2. is the range screw in the middle that people generally screw around with.
3. is the part load stop, it surrounds the range screw.

The quick way to lean it out is to drill a hole through the full load plug of about a quarter of an inch & you will see the range adjustment. Left is leaner, turn it out an 1/8 of a turn & see what your MPG is like, BUT CAUTION, this leans out all throttle positions.

I would read that web page repeatedly, then try & collect a couple of buggered ones to tinker with. If the diaphragm is 1/4 to 1/3 split, you can repair it with silicone. If you want more help I'll dig out my modded one & take some pictures for you. I haven't played with a B20E, but my B30E would get 240+ miles out of a tank with ease + do 130MPH.

Cheers,
Paul.