Flipper feels weak although the coil and linkage are good.

Weak flipper from an over-tight return spring

Cause: The return spring is too strong, so the coil is fighting it on every flip.

Checks

• With the playfield raised, the bats should only just swing back to rest under their own weight.

Fix

• Move the spring anchor to another of the three bushing screws (about 1/3 turn of adjustment each) until it is just strong enough to return the flipper.

Systems

• Electro-mechanical

Related tips

• Flipper weak because the return spring is too strong
• Weak flippers on an EM: adjust the end-of-stroke switch before buying coils
• An EM flipper coil is two windings
• Flippers still weak after a rebuild kit: clean the new EOS contacts
• How an EM flipper coil and its EOS switch work
• Sloppy Gottlieb flipper: loose pawl collar or pin
• Rebuild EM flippers before fitting stronger coils
• Bally and 1948-62 Williams (50 V) EM flipper coils

Source: Repairing Electro-Mechanical (EM) Coin Operated Games to 1978, Part Two, Clay Harrell (pinrepair.com)