Reply To: Johnson RDS-23 1961 40 HP acquired; need general advice

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April 12, 2026 at 8:58 am #315131
Gary H.
Participant

    US Member

    Just a note on Harbor Freight compression tester. I purchased one because I needed one in a pinch while remotely working on equipment in the field. I lent my Mac Tools one to a friend who was unavailable for me to get it back right away. I later found out that the HF brand was WAY LOW in the readings. This was confirmed by me by testing the compression with my Mac Tools one when it was returned to me. When the readings were so far off, I borrowed a family member’s Snap On tester which matched my Mac Tools  one. HF was off by at least 20 psi in a high compression engine.