1. Home
  2. Classic Cars - UK
  3. Balancing twin SU carbs

Balancing twin SU carbs

Balancing the twin SU carbs on my vehicle (A/H BJ8) is a pain as removing the air filters to either use the 'tube to ear' method or a proper air flow meter also requires removing float chamber tops to get at the bolts, which also mount the choke cables etc. - quite a palaver.

There used to be a gizmo comprising a thin walled aluminium tube and some bent bits of wire that let you effectively measure the rise of the piston assembly in each carb and set things to get them the same.

Has anyone used this method and found it reliable and know a UK source of the kit ? (found one Stateside

formatting link
) If all else failsI'll get some tube and start bending wires Andrew Mawson

Reply to
Andrew Mawson
Loading thread data ...

why not add some drillings to the inlet manifold and balance using a set of vacuum gauges?

mrcheerful

Reply to
mrcheerful

No need. I balance SU's by lifting the piston. Use the piston lifter to set the mixture as normal. Then, using the dashpot piston, lift the piston all the way up. This stops that carb working as the mixture goes unburnably weak. Note the rev drop and release the piston. When the engine has settled down, do the same on the other carb. The rev drop should be the same. If not, the carb that gives the biggest drop in revs is doing the most work so reduce it's air flow. Keep testing the mixture and air flow until both are the same. Obviously, this has to be done with the throttle linkage disconnected. It may also be necessary to raise the tickover speed to prevent stalling. If this is done, reduce the tickover by an equal amount on each carb when the balancing is finished.

John

Reply to
John Manders

MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.