As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT COMPLAINED THAT ENGINE WAS NOT MAKING ENOUGH RPM. CHECKED TACHOMETER WITH PHOTO TACHOMETER AND FOUND A/C TOOL TO BE 120 RPM - 140 RPM LOW THROUGHOUT FULL RANGE OF OPERATION. UNIT WAS ORIGINAL TO AIRCRAFT. INSTALLED REPLACEMENT TACH - MITCHELL, P/N DA-112-503. (X)