Dennis from Sachse Tx here

[Treewhisperer2017]

Just got my Zircon Fox with GY6 150cc running. took about 8 hrs. runs really well. Starts easily after it's warmed up. Have to prime carb when she's cold.
Update on hard to start cold and hard to idle.
My intake valve was set to less than .0015 inch.
Exhaust was set to .002
Adjusted to .004 and .005
Motor still would not start when cold. Had to prime to get started.
I replaced the 10 year old carb with a performance carb fro Go Power Sports with a larger jet. Moto starts immediately and definitely has better performance.