Flooding carb issue

[Reckless Rat]

Residual back pressure in the fuel line between the carb and the pump should cause the pump to idle. Perhaps a look at the pump? One of the valves may not be operating correctly.

[graham]

I too had this flooding problem and tried many, if not all, of the suggestions put forward by members of the forum, without success.
Like you I reasoned that it was a pressure problem, possibly aggravated by vibration. My solution was to modify the needle valve by reducing the needle seat orifice to 1.3mm from the standard 1.5mm ( 1.3 because it was the only small size I had at the time). Reducing the cross sectional area increases the pressure needed to open the valve, which therefore is more likely to stay shut if indeed the fuel pressure is high.
I have had no problems since this modification
I should add that this is an RP van with scuttle tank, fuel pump and 26VA carb. Possibly the height of the tank contributes to an increase in pressure.
The cross sectional area of the modified valve is still much larger than that of the carb jets and therefore there are no fuel flow rate issues.