We were talking with a friend last night who was trying to get his dual Dell’Orto carbed Guzzi synched and idle speed set. As is often easy to do, we slipped into over-analyzing what needs to be done and how to accomplish it. Then after a a couple beer’s worth of continued speculation and jabber, we reeled it in and simplified it.
Synching a twin is easy. Here’s how to do it.
Some people are conceptual learners, needing to understand how something works and the approach behind tuning it. Others a procedural learners, concerned more with how something is done than why it works. Both are valid. I’m in the former camp. I’ve found that once you know how something works there are many different recipes for how to do it.
There is only one goal in synching your carbs: To have all cylinders contributing the same amount of effort at any time.
There are three steps to doing this on your twin:
1) Obtaining the optimal idle fuel mixture for both carbs
2) Setting the idle speed screws so both carbs run at the same rpms when the other cylinder is not firing
3) Adjusting the throttle cables so that the throttles move at the exact same time when the grip is turned.
There are some tools you can use to make this job easier or quicker, but they are not required. You can do a fine job of synching with just your ears and a screwdriver. A simple vacuum gauge like one you’d get at the auto parts store will make setting idle fuel mix easier. A motorcycle carb synch tool makes step one and two easier. A tachometer could also be used in place of a vacuum gauge or synch tool for the first two steps.