Flooding SU carburetors

When the B20B engine was idling for a couple of minutes the SU carburettors always began to flood. I played with the floater height, replaced the floater needles, put back in the old ones, took the carbies off..... Nothing really helped. The only result was that I now can rebuild and tune SU HS6 carbies with my eyes closed.

And as the SU HS6 carburettors are mounted just above the exhaust  flooding can be dangerous too!

It must be something else, something outside the carbs....
Well, I fitted a new aftermarket mechanic fuel pump in the car and I've heard that new fuel pumps often gave a higher than desired pressure. And another thing was I fitted a new camshaft with a fresh "eccentric lob" what would cause an even higher pressure (caused by a longer stroke).

Mechanism Mechanic Fuel lift pump

After market Fuel pump Volvo 122S

There are three solutions to solve this; one is to fit an extra or extra thick gasket between the fuel pump and the engine (shorter stroke > less ml fuel/stroke) and number two is to place a Fuel Pressure Regulator (FPR) between the fuel pump and the SU carburetors. Three is to buy an original fuel pump (I'll keep that one in mind if I ever need a new fuel pump..)

A twin SU HS6 carburetor can handle a pressure of ca. 2.5 - 3.0 psi.
To measure the pressure you need to disconnect the fuel line from the carbies and put the adapter from the gauge in the fuel line. The fuel in float bowls will keep the engine running long enough to measure the pressure. It was 4 psi while the engine was idling!

Measuring the fuel pressure

After installing the adjustable Fuel Pressure Regulator I set it on 2.5 psi. No more flooding! As the car is still in the shed I don't know if 2.5 psi is enough while driving it so maybe I've to set it on 3 psi.

Fuel Pressure Regulator in the Volvo 122S

 Btw the Fuel pressure gauge can also be used to measure the vacuum of your inlet manifold. This should be around 18-21 with an idling engine (no matter what engine). Of course I couldn't resist this opportunity... All good!

Measuring the inlet manifold vacuum