My son bought a 4 wheeler not sure of the size year or make. Seems to be having a timing issue, as it spits, sputters, and backfires, but there are no leaks to be seen anywhere. I read through the forums here and it refers to timing them, but when I remove the little oval plate there is only a 13mm bolt head. I think 13mm anyhow. I feel timing is a the issue, but I am not sure how this thing gets timed. Can anyone help. Thanks  

is it chinese?  

yes i am pretty sure it is, as there is no other idenitfiable markings that i can see thanks for your time  

i don't believe it a timing issure unless the previous owner had the engine apart. first thing you need to do is remove the carburetor and clean it. change spark plug,  50-150cc take a ngk c7hsa, (gap .028), change fuel filter  and also do a valve adjustment, if you atv 50-125 chinese send me your e-mail address and i'll send you instructions on how, luvmysxs@yahoo.com