I just finished installing my first kit but when I went to turn the wheels to pedal my bike outside I noticed the back wheel was stiff and was really hard to pedal. It was pedaling freely before I put the motor chain on the bike. I opened up the compartment on the motor to see if the chain was stuck or pressing against something but wasn't. I adjusted the chain tensioner to see if it was too tight but the wheel was still stiff. I did notice one thing though. When I first threaded the chain through the motor I noticed that the chain drive in the motor was hard to turn with the chain tool that came with the kit. I considered spraying it with wd40 to get it to spin smoother and easier but I didn't because I really don't know much about these kits or motors and I didn't want to ruin it. The link will bring you to my bike I'm working on and what it's doing.
*The kit I'm using is a 60cc Aosom kit where the motor is installed in the V part of the bike(between the two wheels)*