Thanks Robert
I do have an inline filter between tank and carb and yes I realise fuel can be contaminated.
What surprises me is I have 2 old trials motor bikes, 2 chain saws, 2 honda pumps a brush cutter and a 4 stroke generator a two stroke push mower and the ride on and this problem is only manifesting itself in the ride on. They all use the same fuel out of the same jerry cans
Is the carb on the Kohler more susceptible to water?