saw it was petrol running low so we went and got some more came back put it in the car and took it out again.
Started jumping again although not straight away so assumed it was the petrol thing and carried on but it kept jumping intermittently and conked out a few times.
How low is low, because if you ran it too low then it's possible that some of the muck from the bottom of your fuel tank has got into the carburettor and that's why your now having running problems.
I'd do what everyone else suggested, but if it's still playing up then it might be worth getting your carb checked and cleaned out.
