1989 Mazda B2200 timing issues (please help)

I just recently replaced the head gasket on my mazda b2200, problem is when I pulled the distributor I forgot to mark it and now I can't get it to start and it keeps back firing out the carb. How do I set the correct timing on it?

Check this site to guide you on this process for checking the cam gear the crank shaft pulley and distributor are lined up properly...