Do what?

I'm confused....lol....not that that is abnormal, but....

So, you have tried three different carburetors and two different fuel sources and the one thing that helped was bumping the timing to 48º plus, correct?

Now you think that you have fixed/helped the issue with correcting a SLE problem and fattening up the mid range circuit, Correct?

If so....I don't know how the timing had any influence with a SLE problem and if it was lean, advancing the timing would have hurt, not helped...

I would assume you have returned the timing to a normal range after you fattened up the mixture and all is good?

If nothing else, makes for a good campfire story....