The only way I see to install an NGK is by cutting away the to fin on the head?! I thought I had plug tight on 2 diff occasions, only to discover leaks after a short time!!! Pissing me off!! Is the ONLY serious flaw I've discovered this far with the YD100 engine, tho. Compared to my stage 4 bbr racing 80/66cc motor, this one crushes that motor IN EVERY WAY...most importantly I pd about $100 less for the bigger motor kit!!! I've prolly got a solid 4 tanks of fuel ran thru her (the bigger sized tank)and she just keeps running better n better!!! I m concerned about the wrist pin clips failing...I had a hell of a time installing one of them and it didn spring back as good as it should have...but I didn know where to get replacements quickly so I went with it. Also leaned out the needle one notch, but haven't touched the main yet. My only b**ch is it seems to rev out too soon and wants to vibrate the bike in half at wot...gonna try re-gearing to a 36t rear sprocket as it has plenty of low end grunt!!!