[KTL]

You've already got large main venturis and very large air correctors that are providing a lot of air to achieve a lean condition. I'd try going down on the main jets to see where that gets you.

I agree it's puzzling that the idle jet change didn't do anything for you. I had a super lean condition and lots of popping at idle one time and my switch from 55 to 60 solved it.

Also consider your e-tubes a place to change. If you go with an e-tube that has more holes in it, that will lean the mixture. I have a set of F24 e-tubes that have a bunch of holes in them and my reading material and internet info have said these tubes are for very large main jets. Makes sense- more holes = more air entrainment = balances out the large main jets?

Don't rule out your fuel too. How good is the fuel you've got avaiable to you in your area?

I think your idle is a bit too rich IMO. Best lean idle adjustment process typically puts you in the lean range (~15) at idle. But obviously its hard to fix that when your adjustments on the idle mix screws are having no effect.....