This has happened to my +2 twice in the last year - the first time I did now recognise it for what it was.
The symptom was a reluctance for the engine to idle, and the engine then dies and is difficult to start. The spark plugs were dry. As I have a standard air box and trunking, I did not see any fuel leakage. The first time it happened the fault cleared when I removed the air box, so I was left in the dark.
The latest time it happened, the fault persisted with the air box off, so I could see what was going on. After much churning with the starter, the engine ran (roughly) and would pump fuel out of an air hole next to the carb inlet. Revving the engine would stop the pumping.
It then seemed pretty obvious that the carb was flooding - the needle valve was probably jammed open by dirt.
With a stubby driver, it was possible to remove the float chamber with the carb still connected to the engine. I then unscrewed the valve with a half inch open ended spanner and blew it clear, and re-assembled the valve and chamber. The engine then ran OK.
This is worth noting if you have Stromberg carbs and the engine dies like this. After half an hour you can be on your way again - if you are careful and don’t drop anything!
Incidently, I have a fuel filter fitted, and I cleaned and coated the tank not so long ago - but there was still a fair amount of red sediment in the float bowl! It must have got past the filter, so I am replacing that.
I also wonder how clean our fuel is from the petrol pump ?
Dave Chapman