Mostly because prople like Andy and Matt have ferreted out snippets of info over the years, and the gen on the HRC unit is that it is designed for race fuels. I have the HRC inline unit, and it advances the ignition as well as delimiting the restrictor, but as far as I know it's ok to use on normal fuel (it has worked fine for me, though I do always run on Super plus or Ultimate. The HRC ig unit is the next step on from what I have.
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