There is a method for balancing carbs using a piece of tubing and your ears--which most people say doesn't work for them, but why not give it a shot? Some SUs also have exhaust emission-control devices to comply with anti-pollution laws. Numbers such asand are sizes: What does the jet do for instance? If it does not, the jet is out of line and you must centralise it. This is not clever regardless of whether you have one carburettor or several — the carb s should always be the LAST thing to adjust.
Anyway read through this book.
Adjusting a Stromberg carburettor
When the engine RPM initially raises as the piston is lifted, and then settles back to the original speed or a little higher, your mixture is right. Nothing like rebuilding your carbs only to find the points were not set correctly I now run a Pertronix electronic ignition …. Turn the tube until a pin on its side falls into a slot in the air-valve shaft. Things were so much easier. If you do not have a revolution counter or tachometer, listen to the engine note. Installed my original ignition with the borrowed carbs. Do not attempt to clean up or straighten a badly scored or bent needle.