And i decided to replace the needle inlet valve on the right hand carburetor.
On close inspection I noticed some corrosion at the seating on the inside of the carburetor cover,
where the needle valve is fitted. This corrosion prevents the valve crush washer from correctly seating,
so this can allow the fuel to squeeze by the valve under pressure. And this was clearly happening when the
engine was under increased acceleration.,,
So the solution was to clean the seat for the valve, and refit a new valve.
You can see the valves in the picture. New one on the left, and old one on the right.
I also inspected the electro magnetic jet more closely. It is a piston operated valve
with 3 equally spaced holes at the end. Petrol flows through the valve holes, and out the
end jet. Problem was the jet was over tightened, which is a regular occurrence on old
vw engines. Apart from damaging the valve, it can damage the seat in the carb. If this
happens the carb is then scrap. Luckily the damage is to the jet, as the holes have been forced oval
but not fully closed. So I fitted a non electric jet here
Here you can see the damaged jet.