HRC card is the only way forward. The MC28 might look cool but it was an exercise in style engineering rather than performance engineering.

Back to back testing has shown a MC21 fly wheel is not any sort of answer to the MC28's limpness.

See below, MC28 fitted with 300 kit. Green trace, MC21 flywheel, open air box HRC jet kit. Purple trace HRC 030 card, open air box and HRC jet kit.



Even with a 300 kit it barley makes 55hp with the MC21 fly wheel fitted, over 10hp gained by de-restricting properly with a HRC card. Without the card a 250 is even less at just over 50hp.

If you have decided to buy a MC28 you have to be prepared to spend the cash to get it to any decent level of performance; ie one that all the other NSR's models (apart from the MC16) can do with little or no expense.
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If I have to take the carbs off once more...