I had a similar problem with my Samson, the bottom of the fuel tank was full of water, like 25 litres.
Due to the construction of the fuel tank, water is trapped between the torsion bar tunnels.
So draining the tank and re-filling does not solve the problem.
You will need to drain tank and remove access hatches and remove all traces of water contamination.
Dont use a shop vac for this.(I did and it exploded.luckily it was outside)
If fuel is your problem , just re-check for water in fuel filter.