It was running ok, now it’s terrible, I need help!!!

Thanks for all the replies. I’ll check compression, while the plugs are out, I’ll pull the distributor so that I can get at the screw underneath, currently the distributor is retarded as much as possible. I’ll also recheck the timing mark with the piston stop, and try to see how much play there is in the timing chain.
I think part of the problem with diagnosis is that it gets much worse when the engine is thoroughly warmed up. The popping doesn’t happen at idle, is most noticeable when just starting out, or when additional throttle is applied, each time the peddle is pushed down, it gives out a pop, generally runs best at higher speed (45 to 55). I have had the feeling, that the engine is using a lot of fuel. Although I’ve put about 10 gal of fuel in the tank, it might still have some bad gas on board.
I’ll get back with my findings
Thanks
Bill