86 TRX70 how do i set timing

[ineed]

Have 86 trx70 it didnt run when bought no spark.replaced plug wire now has spark.needs new gas tank and carb rebuilt .rebuilt carb and it ran when fuel poured in carb until.runs out.but then i thought i removed oil drain plug to change oil ,but it wasnt oil plug it was cam chain tensioner plug and i pulled engine over while it was out and i didnt know it ,i put it back in and now it wont start ,it backfires so i think i screwd up the timing,if anyone outhere can help please .thank you.as my luck always goes,if it aint broke, ill fix it till it iz.