The base number of mixture screw turns can depend on the model of 40 DCOE. I've read that the later emission version DCOEs, like the 151/152 series, require 3+ turns while in my experience, the older non-emission carbs, like the 40 DCOE 27, 28 & 32 need no more than 1 full turn. Any turns more or less than the 'norm' could indicate incorrect idle jets (assuming that the engine mechanicals are in good order). What model DCOEs do you have?
Series 2 USA 1750 GTV (in Series 1 European clothing)