Going to work this morning on my A.R. the throttle would only open about 20mm, I carried on at around 15mph. I took the power valve cover off and turned the "wheel" by hand, it moved right round after a few goes, it felt like something was catching. I sprayed wd40 onto the mechanism and the throttle turned to the stop. It,s fine now, but can someone shed some light on why it happened, Thanks.

Er, confused.com here, the throttle opening dimension, is , mechanically, independent from the power valve mechanism.
What have i failed to grasp from your description of the fault.
Throttle not opening, could be traced to one of half a dozen, mechanical, faults, frayed wire, grit to twist grip, dropping bike on the twist grip side, dual pull chamber fault, and more .
Mike

Hi Mike, I,ll try to clarify. I removed the black cover on the right hand side, when I twisted the throttle, the wheel that the throttle cables are connected to would only turn a fraction, so I turned the wheel by hand. It felt as if it was sticking, then it freed itself and the twistgrip turned fully. I sprayed the wheel with wd 40. I thought that that part was the power valve, but I am a dickhead, the power valve is behind the A.R. cover. Cheers, Kevin.

CR Mmmmm wrote:Hi Mike, I,ll try to clarify. I removed the black cover on the right hand side, when I twisted the throttle, the wheel that the throttle cables are connected to would only turn a fraction, so I turned the wheel by hand. It felt as if it was sticking, then it freed itself and the twistgrip turned fully. I sprayed the wheel with wd 40. I thought that that part was the power valve, but I am a dickhead, the power valve is behind the A.R. cover. Cheers, Kevin.

That would be the , smoked plastic Carb, cover?, the throttle pull, acts remotely to the slide body, so it would appear, that the mechanism, requires, a general service with some WD, or similar.
Mike