Ive been thrown off the '18 once (and broke a load of fingers) and its almost had be again.

The '21 does it too now and again. Bill's been slapped out of his '21 more than once. Bill runs a damper but to be honest I dont get on with them so just hold on a bit tighter.

I think Wayne has also come across it on one of his '18 even after checking everthing.
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If I have to take the carbs off once more...