I now have a CarbMate MKII.
It essentially tells you whether the vacuum on either side of its diaphragm is the same or different. It is thus indicating the flow of air past the carburetor slides when the engine is idling, and thus enables you to adjust the throttle cables of each carb until the flow is the same.
But this is not the only thing involved in synching carbs. Oh, no. It is only one part of the whole process.
I’ve gone and done quite a bit of research into twin-carb balancing techniques. There’s as many methods out there as there are sources on the subject. Some of the better ones are in JB Nicholson’s “Modern Motorcycle Mechanics”, Pete Shoemark’s “Motorcycle Carburettor Manual” (Haynes), an article in the January 2004 issue of Classic Bike magazine, an email to me from Firedog a.k.a. Malcolm Brown, a webpage put up by Hitchcock’s Motorcycles, and a video by Hughie Hancox.
The problem with all of them is that, while they each describe a method, they do not clearly explain the underlying objectives. One thing at least I have gained from being a shrimp scientist is a realization that, if objectives are not clear, a method can end up wide of the mark.
After reading all of them, and thinking deeply about it, I figured out that there are in fact three objectives in tuning a twin-carb motosackle. These objectives can be summarized as (1) MIXTURE, (2) AMOUNT, and (3) TIMING.
(1) MIXTURE of air/fuel entering engine at idle speed to be equal;
(2) AMOUNT of air/fuel entering engine at idle speed to be equal; and
(3) TIMING of slide opening off idle to be equal.
A whole variety of possible techniques, and thus a whole lot of potential for confusion, comes in when other more-easily-measured surrogate factors get used as indicators in place of these three main ones. For example, some methods use the physical dimension of slide aperture (measured by placing ball bearings, or lollipop sticks, in the carb throat against the slide) as an indicator of AMOUNT of air-fuel entering the engine. That’s fine if every other attribute of both carbs is identical, but it ain’t necessarily so.
For a T140 twin-carb tuning and balancing method that works FOR ME, go here.
