Firstly, has it any oil in it? If it hasn't, it will seize as soon as it gets hot. Next, do all the checks outlined above, tank vent, carb clean etc. Auto chokes work the opposite way to what everyone expects, if it has one, it could be on choke all the time. Plug nose would be black and sooty if this is the case, but other faults can also cause this, including a faulty plug, so change that too.