Compression should also be checked, the stock GY6 in excellent cond. should be between 150-155psi, with maximum compression loss of 15%. So anything below 127-131psi will effect the engine mechanically. A single piston engine don't like to start cold. The fuel enrichment valve if bad will give you a rich mixture when engine is warm. If the enrichment circuit is pluged up you will not get tthe extra fuel when engine is cold. I believe in one of the earlier posts it was mentioned they changed the carb.
TOM
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