Try adjusting the air pump by turning the screw counter clockwise. You can also spray a little WD40 onto the shaft that the reels are on. Be careful not to contaminate the reel strips with the WD40. Use as little as possible.
Ron
How mechanically inclined are you?
The piston works like a bicycle pump. There's a leather diaphragm that acts as a seal. They dry out and leak. (lose air)
If the seal is only dry, I use Vaseline to moisten it. If it's deteriorated, I cut a replacement from similar leather, lubricate with Vaseline, and replace.
Adjust as previously suggested.