Symptoms: Engine ok at full gas, but flooding, dying and stalling at idle. Fuel consumption between horrendous and catastrophic.
Carb was new as well as the 175cc kit (fitted into a Series 2 winter model).
-Took carb out. checked float: OK, full movement, no sticking, not punctured
-Checked float needle. Blowing from the petrol feed tube, as soon as gentle pressure was applied to the float, cut supply immediately.
-And then: choke testing. Blowing through the choke jet, choke on or off produced no difference.
Took choke plunger out and looked ok, sealing rubber was new, not even marked, but the brass flange where the rubber sits was too thick.
I had a spare choke plunger lying around, new as well, and was different, flange was thinner (see pic)
My carb was badly machined and the choke jet sat off centre, so the thick one fouled on the jet and could not seat well. The thin one sat ok.
Went for a ride, perfect idle. Problem solved

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Wrong one is on the left, good one is on the right
Worth checking before ditching a good carb.
Happy sunday to everyone
Robert