71 LA 340 timings moved!! how?? looking for help

Hi... its fine when cold and idles, but once warm its does this and its a slow crank for a split second from the get go, like I said the engine just feels too hot for the short time it runs, it then constantly stalls, I struggled to get home lol!! thing is it was timed at 32 at idle before hence this post and now only 17.. so very confused... I'm thinking I may have a sticking valve causing the loud backfire. thing is engine has so much upgrades its hard to figure where things need to be... I've triple checked plug wires and they are correct