B & S 35 Classic?

Quite bizarly we have two petrol mowers in the family and both now suffer with the same problem for example: They start fine then almost immediately the engine starts 'hunting the only difference being one stalls whilst the other will keep going albeit the engine 'hunts.

I have checked all the obvious points and resigned to now taking at least one of the carbs off to check as I feel it is petrol related.

Has anyone suffered the same here and rectified it?

Any info would be gratefully received.

Thanks Barry HH