I just gave it a test. It levels off now a 13.5 psi. A bit higher than spec.
Noticable improvement in acceleration. I might try a small added shim.

I wouldn't attempt to do this without a pressure gauge.

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85 Merc 300D - Unwinding 31 years of wear
86 VW TD
Mahindra Diesel
Iseki Diesel

In 2007 I didn't own a diesel.