Just a thought regarding vac advanceHard to express. Put your foot down in low RPM's and it is sluggish and sometimes we get the dreaded detonation in the inlet.
Press gently and it gradually picks up and then the cycle repeats for your next gear change occasion. BUT, have it revving nicely and it will keep pulling. e.g. Up a big mile long local hill I was doing 50 in 4th gear and it still wanted to pull.
Summat isn't right and I don't want to just keep throwing more petrol in the bores as I have no idea what the AFR is, or if it is still a timing issue.
Putting your foot down retards the ignition, lifting it off advances ignition to allow for leaner mixture.