This comment presumes 2 things:
1. that your ignition is in excellent condition, firing that very rich mixture, and that you have at least X24ES-U plugs, as the D8EA will not cut it at the 12.5:1 A/F ratios you are now running...
2. You are NOT using Keyster parts in your carbs.
It sounds like you are going through a transition zone where it's going from too rich to about right in the mix. Chances are, the combination of air screws WAY too far out (should be at 7/8 to 1-1/8 turns, regardless of bore size) and needles shimmed above the 5th notch are making it impossible to maintain that very rich mixture to WOT settings.
My suggestions (other tan not using Keyster parts, which has been posted to death):
1. Most important: vacuum leaks in the carb boots. If they are hard, get new ones or soak them in a wintergreen and xylol mixture for a few days until they soften up again. Once they are hard, no amount of clamping force will seal them.
2. Turn the air screws back to 1 turn.
3. Put the needles back into the clips, starting in the middle position.
4. Go to a 115 mainjet.
Just because the engine was bored does not mean it has to be richened up to run right. Normally going to 836cc involves little more than boring and reassembling, so long as the quench band was added in the head to control the increased compression. Barring that mod, rasing the mainjet from the typical 110 or 105 stock size found on most 750s, up to about 115, is plenty. If the plugs were still white after that, something else is amiss, like too much spark advance, too much vacuum leakage, or poor fuel delivery from incorrectly set float bowls.
The latter is a Keyster trait, as are the problems with their needles, BTW...
