My GH250 cuts out if I apply a load (it's on a big Ransomes lawn mower). it just runs for a few seconds and sort of "searches" for something, but eventually gives up and stops
I can then be restarted with a simple pull on the starter. Oh it always starts first tug, always has.

It's got plenty of fuel, and I have cleaned the carb with an air line squirted into all it's little places
I removed the air filter and it makes no difference.
I then noticed the little fuel filter was full of bits, so that's now clean.

It does appear to be running quite rich - the plug is sooty, but that might be because its only been started and not run on load?

There is no adjustment on the carb for things like float level, it's a fixed position.

Phill