A carb balance should ideally be done after a full service including a valve clearance check, you can however give it a quick check any time you feel the need. I got some CarbTune Pro (same as the CarbTune 2) vacuum gauges as I had heard good comments about them and for the money they seemed the best option. You can expect to pay anything from 40-170 pounds for a set of four gauges, the CarbTune costs about 55 pounds.
They are stainless ground columns that run up and down clear plastic tubes, you can also get dial gauges and manometers that carry mercury in tubes, they all do the same job and that is to measure the vacuum created through the carb, which is what sucks the fuel through, by balancing the carbs you are making sure they are all sucking the same amount of air and fuel.
Ok now I had just finished doing a Valve clearance check and fittted new plugs it also hadn’t been long since my last oil change so now seemed the right time.
First up you need to warm the bike up, then remove the tank and the vacuum take off caps from the carbs so you can connect the vacuum tubes from the gauges, you can hang the gauges from the handle bars or prop them up against the clocks, at this point you will need to set up a remote fuel supply, this is so you can gain access to the carb adjustment screws (which are obscured by the tank) whilst still running the bike.
You can get extended fuel lines for the tank, sometimes you can turn the tank around and place it on the seat or have a separate bottle/container connected into the existing lines….mine was somewhat of a hash up laughingly made of two turkey basters buchered and pushed through an old washing up bottle ! eat your heart out Blue Peter !! but did the job anyway !
I had already sized up where the adjuster screws are on the carbs and bought a long screw driver to reach them (as in the first pic) . I found it needed to be about a foot long to poke down between various stuff to comfortably reach the adjuster screws.
Start the bike and set the idle via the wheel at the side of the carbs,
It should be set at 1000 RPM give or take a little, this will set No.2 carb, this is the base carb in the 3 cylinder lump. Then watch the gauges and see if either cylinder 1 (at the left) or cylinder 3 (at the right) are close to No. 2, ie within 2cmHg of one another according to the CarbTune manual.
Haynes states 127-152mmHg so basically the same really. You can see the scale here…next time I’ll insert a little video so you can see them in action next time I do it !
If they are slightly out twiddle the relevant screw a small amount until they are as close as possible, give the throttle a blip and make sure the readings are still the same. Repeat as necessary until you are happy with the readings.