you could have blocked up carbeurettors.
if you filled all 3 lawnmowers up with the same petrol can, and there was some dirt in the petrol, it could have blocked up the jets.
Remove the carbeurettor, then unscrew the idle jet(if you have one) making note of how many turns it took to remove the jet, do the same for the main jet, and soak the carbeurettor in petrol. shake it out and spray down the holes where the jets were with an air compressor, put the jets back and put the float chamber back on, then put the carbeurettor back on and fingers crossed it should run.
it might take a bit more pulling on the chord to get the mower to run as you will have to pump the fuel through the carbeurettor.
if this doesnt work, try cleaning out the air filter
Stephan
May 2007