Worn out sleeves are often the cause of sluggish movements in a pinball game. It may not be the only reason but its a good and cheap place to start.
Shown left here is a side angle of the left slingshot assembly on The Bally Game Show. The mechanisms are in great shape with need of a good cleaning. However even though the return spring is in great shape it does not provide as powerful a kick as it should and does not retract very easily after hitting the ball. Testing the mechanism underneath manually I discovered that it does seem to have a lot of friction.
After removing the assembly I was able to check out the small plastic sleeve inside the coil. From years of action it is worn from carbon buildup and overuse. After seeing this, I can deduce that this is most likely the culprit to the malfunctioning slingshots.
Side by side the new and old sleave. The old one shows obvious overuse. Coil sleeves range in price of 40 to 80 cents (USD) so its not a huge investment to replace them. After cleaning the slingshot mechanisms with some alcohol and a cloth, I installed the new sleeve, cleaned the leaf switch and reassembled. I hand tested the mechanism and the plunger moved in and out of the coil with ease. I tested it with a game and the slings were twice as powerful as they were before.
Oftentimes its a simple solution such as this that is needed. Other times it is not. Worn out coils, plunger mechanisms, and leaf switch could be to blame for weak action. Coils last a long time. It is not impossible, but unlikely that they are to blame. My 1980 firepower has all original coils minus 1 so they last a long time. Switches can go bad, especially the end of stroke switch on flippers. Often cleaning will improve performance. If there is too much play in the plunger linkage it will cause more friction as well. Rebuild parts are readily available.
