Hayter Harrier 56 Briggs and Stratton Quantum engine choke won't close

[SamMowerman]

Hello, I have an old Hayter Harrier 56 which stopped working a few days ago. I was mowing the lawn, and I think it ran out of petrol, as I couldn't see any in the tank. I filled it with petrol and then when I pulled the starter cord, the engine was very difficult to turn over. There was a very hard part every so many rotations (probably only one of the four strokes), and I couldn't get it to start. I drained out the oil and found that there was probably about 200ml in it, and I believe it needs 500ml. I refilled the oil with brand new Hayter engine oil, but the difficulty turning the engine over remained, and it won't start.

I started to take it apart, so I could see the carburretor, and I noticed that the choke doesn't close when the lever is set to the 'tortoise' position, for full choke. I can see that there is a rod that goes to the metal part on the top, which the choke is attached to, but the rod doesn't move back to close the choke (and I presume there is nothing else supposed to do this, unless there was a spring which has gone missing). I believe this rod is somehow connected to the governor on the engine. Should this rod be moving backwards (to the left on the photo) to pull the choke closed when the choke level is on the 'tortoise' setting? You can see that the cable is as tight as it can be, on the top right of the photo. I think in this photo I had manually adjusted the plate which is pointed at by the arrow in the centre of the photo, to close the choke, so it doesn't represent what actually happens when I try to turn the choke on with the handlebar lever.

Many thanks in advance to anybody who can help me, I appreciate you taking the time to answer all the queries on here.