Steven Campbell laid this down on his screen :
Bought a petrol Ryobi brushcutter yesterday.
I was under the impression that once the motor was fired up, the cutting head
would spin all be it slowly
If I pull the trigger and the revs go up considerably, the head will spin but
as soon as I introduce it to the heavy overgrowth it stops spinning. Its not
until I have it revved up to the full amount (or at least it seems that way)
that it will spin and cut without problem
Is this correct?

They have a centrifugal clutch at the output shaft just beneath the
engine. It only starts to engage as you open the throttle, so a light
throttle opening will not fully engage it and it will stop under load.

You shouldn't use any throttle setting but full and tick over.

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Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk