This is WR, but the basics are roughly the same.
Under the yellow cap, the idle screw.
Turn clockwise, reduce idle speed. Turn to far, and no idle.
Turn anti-clockwise, increase idle speed. Turn too far, and the engine may well stall, along with suddenly having a big brass screw in your hand.
Close up of the mixture screw. Or rather the tube that gets to it. Hence using a long handled 3mm Allen key.
Mixture adjustment. If it's really sooty, gross adjustments of a couple of turns. Fine adjustments ¼ turns.
Another thought.
If that was what occurred with the fuel system, how is the engine oil?
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