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

What have you actually DONE, besides play with the timing? I outlined how to check timing marks which in my head is absolutely essential

Hi 67Dart273 very helpful post I'm sure I'd seen that pic but can't see a post from you with this???... sadly the internet and forums are hard to communicate on at best of times as so many people and misplaced info can be put out there.. mainly the "dreaded vac hooked up or not" I did say its NOT running vac advance at the start but sadly people still not seeing it.... why its not? I really don't know but there is a small bolt in the end of the hose the other end is connected to the Holley 750 so its not fallen off and remember I've covered 100's of miles with no issues and crazy power, took me a few drives to get used to the power as it just wants to spin out lol!! back then anything more than 1/4 throttle would result in tyre smoke at any speed.. anyways... my piston TDC tool as just arrived from Summit today, can't buy such a tool here in backward England... so will now follow your guide and links tomorrow as its 15:25 here and already getting dark and very windy :-(
I've done a little more than just played with timing... but countless times I was told to just "retard the timing already" but I wanted to figure why it seemed to have shifted but went ahead and did it after checking a few things., to which point I'm now very loud backfire out the tailpipes if I give anything more than cruising. I get one loud bang and I lifted!!, refuelled and same again, on a side note I've now noticed previous guy had white marked on the crank pulley where its at now at 17 at idle of 950-1000rpm.

I have made sure

1. the timing/crank pulley had not spun, which it has not as all timing marks line up when dist rotor is pointing at No1 and at least roughly TDC on No1 bore. but kind of knew this as its running bad so obviously an issue.

2. I have checked for timing chain slack, although its only covered around 1200 miles since full rebuild and not abused but to be honest I'm getting pretty much instant movement when turning engine back or forth so seeing zero noticable slack.

3. checked the timing mark was not jumping around as someone stated in regards to electrical work I had done, but guy confirmed the dist was not touched from the ballast to the dist and its not jumping about its got a very tiny amount of movement, but it increases and decreases smoothly.

4. I had checked the distributor for anything obvious but seemed OK but I'll put my hands up, not sure how I remove the insides to see the springs we speak of... right or more like wrong I assumed that..... they were OK as advance is stable and smooth increase decrease. My bad..

I've looked online and finding nothing, but was hoping for a step by step guide to rebuilding the distributor be it text and photos or video but all I find is Chevy/GM stuff.. Does that pick up wheel just pull off? heck I just don't want to break anything as very little is on shelf here in the UK unless you drive common American cars.. Vett's Mustang's, Firebirds, camaro's, 80's trucks, caddies, Dodge Rams, etc

Someone mentioned if my Dist is stock it needs work?? did not understand that? as although its a factory unit its converted from points to elec, weights and springs changed to get required curve? so not what I'd call stock??

May sound strange to bring it up.. but I suffer from an illness M.E which does effect my brain processing, speech (and text) get confused fairly easy along with cronic pain 24/7 so not asking for pity but a little "idiot cushioning" as also dosed up on fentanyl patches for back injury.. its safe to say my car is in better shape than me and both 44 yrs old... But I refuse to give up my passion and ownership of my life love of American vehicles.. I even have a disabled parking permit for the Duster lol!!