Here's a question: Do you lot know Dave Whattams...Mutt's Nutts? He's a well known genius in the LC world when it comes to setting up LC's in particular difficult hybrids. With his dyno and incomparable knowledge of what people will and can do with those motors he always finds a solution. https://www.muttsnuts2strokes.co.uk/.

Anyway, I asked if he would be willing to take a look at my carbs if I sent them over to him and he said : "looks like ifs an MC18 or MC21 model, always hard to tell from a picture, anyway, my point being doesn’t it have the solenoids on the carbs ? If it does have solenoids on the carbs, just try blocking the rubber tubes off for the front cylinder as if the solenoids fail they can fail open, which means the air corrector circuit is open and will cause it to be lean, hence poor starting/idling etc"

I suppose I should know the answer to this but checking in with you lot: does the MC18 have solenoids?