My U800 hat bad brakes.........air in the system. It's a common problem..... In a service protocol from CF Moto there where the following 3 steps to do:
Step 1: Bleed the brakes Front and Back as usual done.....If that helps........your done. If not:
Step 2: Pump the brake peddel 20 times in 10 seconds and hold the peddel. Bleed the brake at corner left-front. Do it again with right-front, again with left-back and again with right back...........If that helps, your done. If not:
Step 3: Separate the front brake lines from the back brake lines; block it with a screw..??.. Then step 2 again.... your only have pressure on the front or on the back. If you are done and it works.......super. If it's not working replace the hole break.....!!......
Step 1 and 2, I can imagine that will work. Step 3 is a big nonsense. By opening the lines there will be air in the system again......
After doing step 1 carefully the brake was fine.....
PS: Fill after 1 bleeding attempt new brake oil in !!!!!!!