decreased suctionon CW vacuum

I have decreased suction on one of the vacuums. It is coin operated and has 2 motors on top. If there are no blockages is it time to replace the motors

check the brushes on the motor, also my je adams have cloth tubes that connect to the bottom of the motor inside the unit and very often those need to be taken out and banged out. seals on the cleanout door make sure those are fully attached as well

Open the top service door and run the motors, then look up at the bottom of them and you'll probably see one not running (If there's not a top door, open the clean-out door and take off the dome before you start it). If one motor fails, most of the suction is lost through it. You need to open one of the doors or you won't see which motor isn't turning - the airflow will spin it.

Most times MEP is correct. Even with two motors you can get relatively good suction. You can definitely notice the difference with one motor out.
I have also found both motors running with poor suction. So I replace one of the motors - I have not reason for this except perhaps that some lint became sucked in and was inside the motor. The other thing is be sure your bags are not clogged too much. You can reach up and manually shake the bags. Best thing is to take the bags out occassionally and wash them in the washing machine. Be sure there are no holes in the bags since the lint and stuff leaking through will slowly deminish the suctin power of the motor. Check your vacs hose for leaks. You can find if there are holes or cuts in you vac hose by taking it off, plug the other end with towel and filling it with water from a hose. The leaks will expose themselves.

Main sure gaskets are good on the doors, and also no leaks where the hose enters the vac and no leaks where the nozzles connect to the hose. Also you can have leaks where the motors mount on top of the vac.
Basically you need an airtight system - meaning the only incoming air is from the nozzle.

Most manufactures have a screen under the motors, check and see if this has built up lint.

I was having the same problem on a 2 motor, 6 bag vac. Customers knew the suction was less than my other vacs and it got very little use. I followed the steps in the replys. (holds in hose, door gaskets, or dirty bags) The bags were the culprit. They were "dusted" weekly but I didn't realize the inside of the bags were "caked and crusted" over so very little air was passing through them. I beat them against a service pole to break up the crust and took them to a coinop laundry. (sorry laundry owner)The results were AMAZING, it works like new!! PS I also checked the screens under the motor mounts-no air mens not trash or lint!