| I also own a pair of z1's and overall they have been good, with only little annoying problems as you would expect from a chinese bike. No major problems.
I also own 2 polini 911 replicas and have had none of the crank-shaft problems you have talked of. 1 has a polini race crank now only because i put a bizeta 6-port top end on and wanted that extra bit of security. The other bike runs the polini 50cc topend with a standard crank and has not had any issues. The clutches are crap-non adjustable items on the 911.
The chain guide on the z1 is useless, just throw it away. The z1 is probably the closest chinese bike to being ready to race out of the crate. You will need to file the brake mounts on the forks so they float a little better. Drill the main jet to 0.96 mm, remove the chain guard and you are off.
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Trying to get more people to pocket bike events held around Tasmania
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