Finally got the chance to look over the mower in a bit more detail. The engine was running a little rough so I checked oil (ok), plug (ok after a clean) and air filter (very blocked but now fully cleaned). What a difference, she starts first pull, idles smoothly and runs smoothly too. I will put in a new air filter but I've sorted out cause of rough running.
Here are a few pics of the drive belt and chains, chain and sprockets look alright but belt will need replacing as it is a little frayed.
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