Yeah there was slack, I loosened it all the way on the throttle adjuster and could see the slack at the throttle stop but it was still stuck/idling high.
I was looking through the throttle plate forums and read that a little bit of light is ok(?).
The throttle plate stuff looks a bit tricky, and would rather avoid it, but I can see the screws on the throttle plate on one of the carbs have been rounded out a little. So its probable they haven’t been centred right. Here is a photo of both the carbs and the light that gets through.