Guys its usually less about the eggs and more about the acidity of the lemon, so don't use lemon other than as flavoring...use vinegar first, then thin using lemon juice as required. Lemons have different acidity at different times of the year and with different varieties...if you have a failed batch of mayo, keep it, start again and instead of oil, add the failed batch of mayo as you would the oil. You should have fixed your 'split'.