After cartridge replacement in Moen 7840SL & dis-assembly and cleaning of side spray, when assembled and using side sparay, water still runs out of main faucet as well as side spray. Previously when side sparay was used all the water would be diverted to side spray and no water would run out of main faucet.

Diverter valve not properly re-installed or defective. When you allow water out the side spray the flow of water closes the port to the faucet spout. Check installation of valve.

Great advice from Harold. In addition, there may be speck of dirt in your faucet / diverter disallowing it to switch from spray to spout. As Harold suggested, you will have to take it apart, clean it and reinstall it. Back to you. Milo