Oil does have an effect on it as when I changed mine for 0w-40 it was less harsh but still noticeable. Mark at abbey did explain to me what was actually making it do it but I can't remember exactly what it was now. The timing on the hr is electromagnetically adjustable and goes out of target that's why you get the stutter. If you give mark a call I'm sure he will explain all and get you booked in for an uprev! Mine drives so much better since the uprev. They should come out the factory as smooth as mine is now.
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