Mountfield petrol mower (Theale RG7)

Lawn mower with Briggs & Stratton engine as shown
For spares or repair.
Having worked well for the past 8+ yars it has developed a starting problem. It fires and then immediately cuts out. I have replaced the carburettor, fuel filter and primer pump, but still no luck. Should be a simple job for someone happy to tinker about with it. I just need it out of the way because I have replaced it and I don’t have the time or skill to fix it myself.