You will always slip with an er3. That’s the point. That’s how the “clutch” action works. If you slip all the time then you’re either not getting enough spring resistance to give the tension on the belt that’s needed (most likely as 1000 is the weakest spring available for scooter setups) or your weights aren’t heavy enough..... but it’s your spring I’m pretty sure. That’s why a launch lever and/or a stronger spring/gas shock is whats needed