I had a friend work on my 1976 yamaha enduro, it spits smoke out like the bat mobile. He bought a spark plug for it that he said was a 10? He said I should use an 8 or a 6 if I want to run the bike hard. Can anybody tell me what a 10 vs 8 vs 6 spark plug is? Or what you recommend for usage of it? Also where I can accessories or spare parts for it?