For your modifications, anything bigger than a 155 is just too big. Have you been riding the bike or just letting it idle before checking the plug? It should have some type of deposit on it riding it like you stole it before you pull the plug. Post a picture of your plug. If you have a camera with a digital macro setting, select "macro" and this will enable you to get close up to the electrode area. Post it up your picture, or sen it to me at imabeachbum2001@yahoo.com.
~Brian