Hmm doesn't look smart.
But I'd say it's ok as long as it's wet so that the dust doesn't get inhaled.
Craziest thing I've read in a workshop manual I own is how to tune underload with two people.
One person stands idles the car balances the clutch and brake and accelerator to put the car underload whist someone adjust carby settings.

One slip, flattened carby adjuster.
It was not in a mini manual I don't think though.
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1964 Morris 850, 1330 Supercharged - 81.8hp atws.
1975 Leyland Mini S 1100S powered - Nice and reliable.
1977 Leyland Mini LS - Project LS-T
