. The larger sizes quoted by Jha and HRC are for use with pre-mixed, race octane rated fuel.*

*Normally the oil is injected by the pump downstream of the emulsion tube nozzle, but with pre-mix, the oil is in the float chamber, already mixed with the petrol (gas). This means the fuel passing through the MJ is weaker than normal (oil is now making up 3.2% of the volume @30:1) and so a larger size is needed to compensate. Don't even bother trying to run Jha's base sizes until you've removed the oil pump and thrown away the airbox, it'll run like shite!!

This is what it says in tuning in jetting section
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MC21 SP