Wouldn't it be an easier matter of just changing the coils?

Are the correct coils installed?

Is the transformer set for high tap or normal tap?

Can also weaken the flipper action slightly by setting the EOS switch to open earlier and putting a stronger return spring in line. Does Blue Chip use the Williams design where the return spring is coaxial with the solenoid plunger?

You may be looking at this the wrong way. What are you comparing the action to? All of my rebuilt WMS flippers are fast and snappy, like they should be. If your comparing WMS flippers action to Gottlieb, than you will notice a large difference in the game play. You want enough power to get the ball up to the top with ease and crank on those spinners!

What degree of tilt do you have the table set at?

Did you check the transformer settings?
Is the high power tapped?
Do you have the correct return springs?
What is the current playfield inclination?
Has the game been recently shopped and flippers rebuilt?
Has the playfield been recently waxed?
What is the comparison to any other titles of the same period and manufacturers you may own?

Ask yourself these questions for initial assistance.

This easier than anything else stated above.
Setting the EoS to open earlier should not be required.
Don't jump to adding unnecessary electronic components that were never recommended or approved from the factory or update bulletins.
If the game has the factory coils, an owner should not need to modify anything.

If you feel the game is still too powerful, elevate the angle of the playfield by approximately 1-1.5 degrees BEFORE modifying the transformer settings.
Don't "fix" things that do not need to be repaired, including lack of math calculations with resistors.
Technicians classify this as a hack, as it rarely restored to the original factory specifications when a game is sold at a later date or something else goes wrong.

My estimate is your game was tapped for higher power from the transformer by a former owner or operator that wanted the flippers to be "hot" due to lack of interest in performing maintenance.

The best way to micro-manage the flipper power (assuming they are too strong) is to adjust the EOS switch on each flipper. If you give it a big gap (that is, the EOS switch opens much sooner), it will decrease the power of the flippers. This is a really easy change to make, totally reversible, and takes but a few seconds to adjust.

For example, on Bally Wizard, we like a really strong right flipper (to make that long loop shoot to the top.) So we put a 28 volt gottlieb 5141 coil on the right flipper. This is WAY too strong for a 50 volt game! but by adjusting the EOS switch, we tame it down so it's the right power level. There's probably a 1/2" gap when the flipper is fully engaged!

Do you have the proper coils? Looking at the schematic it looks like it calls for FL-20-300/28-400. Also, maybe someone removed some turns of wire to add to the flip strength - any evidence of removed wrapper and resoldered wire by the lugs?

Are the flippers at the correct height, and the flipper ribbers in the correct position on the flipper bats?

You shouldn’t be able to directly hit the wire that goes from the spinner through the playfield. Shouldn’t there be a post that protects that?

Rebuild kits don't normally include coils.

On Williams Blue Chip the Jet Bumpers and Kickers run on DC. It would have been easy for a previous owner to change the flippers to run on DC too, which would make them much more powerful.