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Idle adjustment is on the top left on the carb as you face the engine. Small brass screw with a point and spring also connected to the throttle linkage. Turn very slightly.

If it idled fine last week and suddenly not not fine now, I doubt raising it will do much to help this. Mine idles at 800/900 RPM, and 600/700 in forward.

Hopefully a high does of seafoam will help (I mean high does like the whole can in 3 or 4 gallons) It will smoke...

I know this may sound stupid but is the vent screw open, I've done this, just last year...:D

Screw vibrated to the closed position...