Restoration Volvo 122S 1969: Rebuilding the SU HS6 Carburetters

The double SU HS6 carburetters were covered in a mix of grease, oil and mud. As I bought the car with the engine in bits I didn't know in what condition they were and decided to clean them thoroughly, dismantle them and do some rebuilding.

SU HS6 carburetters AUD331 after 13 years collecting dust

The rebuild kit you need for these SU HS6 carburetters is CRK 249. This kit doesn't come with the jet needles as they vary depending on the engine and carburetter number. The labels on the carbs indicated AUD331, so according to a needle chart I needed spring-loaded needles with code AUD1538 KN.

Rebuild kit CRK 249 for SU HS6 carburetters

Needle chart SU carburettors Volvo B14 B16 B18 B20

Needle chart SU carburetters Volvo B14 B16 B18 B20

The rebuild kit came with new throttle flaps and shafts. To use them you need to ream out the old bushings and then press in the new ones which is something for a specialist. The reason to replace them is that false air can be sucked in through the space created between the shaft and the bushings after many years. I decided not to replace them to save some money. If leaking, the carbs can be easily removed to bring them to the shop for the in line reaming.
After cleaning the outside of the carbs with turps and alcohol I disassembled the first one and made pics of every step so I had some reference material when rebuilding. I think it's been the first time the inside of the carbs saw daylight in 43 years. I discovered that the needle in the second carb wasn't fit correctly.The mark/line on the needle guide should point away from the ports in the piston/air valve, so the needle leaned in the wrong direction which caused severe wear in the jet and on the needle itself.

Dirty Air valve SU HS6 carburetter

Air valve SU HS6 carburetter with spring-loaded needle,
note that the needle isn't installed correctly

Air valve with guide, spring and KN needle

Inside the SU HS6 carburettor

Old jet with KN needle SU HS6 carburetter,
see how the jet feed pipe fell in bits when disassembling

Replacing the spring-loaded needle and jet is pretty straight forward and will take only 15 minutes or so.

When replacing the needle make sure the needle guide is flush with the piston and that the mark on the guide points away from the ports in the piston. The jet assembly is hold by one screw and one bolt which connect the float chamber with the feed pipe.

With most SU carburetters you need to centre the jet after replacing the needle and/or jet. But with this one it's not possible and thus not neccessary.

Spring-loaded KN needle and jet in SU HS6 AUD331 carburettor

Spring-loaded KN needle and jet close up

I also replaced the needle valve and seat in the float chamber and checked the float level (ca. 4.8 mm).

Another thing to check is the damper piston clearance. Don't be fooled by the Haynes manual, the right clearance for the AUD331 carbs should be 0.4-0.8 mm.