RE: throttle arm Become difficult to move dz160
This usually happens from the engine overheating, and warping the carb housing. causing the barel to jam when the motor heats and expands.
Remove the throttle barrel and sand it with 2000 grit paper Wet ,and replace if it persist, replace the carb housing. asmbly.
Be carful not to tighten the carb housing to much this can also warp it and cause the issue.
make sure the engine is receiving enough cooling through the cowling and make sure the pump housing also has direct air flow.
Bryan