One ball and no flippers! I'm impressed!

Re kicker strength:
1. Clean the kicker solenoid plungers and plastic sleeves. (Don't lubricate)
2. Read the schematic to find which switches are in the kicker circuits, and sand or file those switches.
3. Check the voltage on the transformer
4. There are modifications you could make like removing some of the turns of wire in the solenoids, move transformer wire to high-tap, or put in a rectifier to run the kickers on direct current.

If they work and score properly when you push with your hand but do not respond when ball hits them it may be just the switches not set properly. Check the gap for the switches behind the rubbers. Clean them up and maybe set the gap a little closer so ball will activate when hit.
Also... Is the rubber the right size? If it's too small and too tight maybe it's pushing ball away before kicker switch is activated.

Chillyh20,

Follow Chum43 advice. Not knowing your experience with pins ignore the advice you don't need below.

With the power off, remove the lock bar, then Backglass and lift the playfield until it is resting on the lightbox with a rag or such between the surfaces to avoid scratches.

You now have access to the kicker assembly. Examine the kicker assembly for binding, cleanliness, and the activating switch contacts. There is a spring in there too.

I would take some pictures then disassemble to clean the contacts and the plunger and coil sleeve. Reassemble and ensure the switch contacts are about 1/16 " or less apart.

Don't modify the coil kickers they don't need this just be clean and the correct gap.