I just bought a new 50cc. It didn't always want to stay at idle, so I bought a new NGK Iridium plug and filled up with premium gas... I get home and gap the new plug to .0265.... So, I pull the what I thought was a Chinese plug, but it was a
NGK C7HSA! I should have had more trust in my bike dealer :P Anyway it was gapped at .028... I did the swap out anyway and no longer have any problems staying at idle
I think the smaller spark contact on the iridium allows a better spark. The wider contact area of the basic NGK spreads out the electricity and probably does not get a nice hot spark at low RPM's... The acceleration from a stop feels smoother, but maybe its just me
-Shane