Hi. Try cleaning out the slow running jet in the carb the hole is very small and gets blocked very easily. If this is the problem the tickover will also be improved. another area to look at is that magneto coil may be breaking down as it heats up. Please take a look at scorpa not running for my comments on that problem.
Hi. I had the same problem with my 250 Easy in the end it turned out to be the magneto ignition winding not putting out enough power got a scorpa flywheel extractor from Ringwood Precision Engineering they are on ebay and a tool to hold the flywheel they also supplied test regulations for the magneto. It is only one coil that burns out and is the ignition coil. A local motor rewind company rewound the coil with the help of the test regulations. Cured problem completly starts first or second kick every time.