This is exactly the problem that I am having with own MC21.
Set up as per the the method to which Tuckerbag is referring my bike spatters oil all over the rear end and runs very lumpy low to mid throttle. It also smokes like a badly smoking thing!!!
I've tried two separate pairs of carbs, rebuilt and cleaned. Different main jets with all other jets std...still the same.
Mike
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I don't mind dying...I just don't want to be there when it happens!