Have you swapped the power valve servo motor? How are the power valve cables? Do they slide freely? I have read that sometimes the power valve servo and/or power valve cables will get frozen/jammed up, causing the PGM to blow.

Larry
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1993 Honda NSR250
1989 Honda NSR50 (100cc bore up)
1992 Honda NSR50 (80cc Engine)
1993 Honda NSR50 (Project bike)