Slash2 wrote: ↑Mon Apr 08, 2024 9:12 pm
I think this whole differential timing mumbo jumbo is for the most part, a great big nothing burger.
I strongly disagree. I order to make the engine run
perfectly with little or NO vibration, you must have 3 degrees or less differential timing.
If you have a lot more, you will wonder why you cannot balance and synchronize the carbs. The reason being, when you pull a plug wire, to set the idle air mix, it will run on one side (that is the cylinder that has the advanced timing) and it will die on the other side (the one with retarded timing) every time the other wire is pulled. So, on the cylinder that won't run, you'll attempt to set the mix by speeding up that cylinder, by raising the slide, until it will run. Then you'll mess with the idle mix, and in most cases, you'll wonder why the carb
will not respond to idle air mix changes. The reason it won't, is because you raised the slide enough that it begins to run off the main jet. So when both plug wires are attached, it will run fast, and vibrate, and slowly opening the throttle to check sync you will discover one appears to be opening before the other, and will adjust the cables to compensate. Yet it will always have vibration and never be "perfectly" smooth.
Another symptom of differential timing, that you can notice just at a glance, is that one header pipe, will be
MUCH bluer (the one that is more advanced that is doing all the work, the other is following along) than the other.
If there is
NO differential timing, BOTH cyls will run one at a time, with the opposite plug wire pulled, (as it should) and the idle air mix can be properly set, AND then carbs
can be synchronized to open both slides at exactly the same time.
And you will be amazed at how little vibration the bike will have at any speed. And how much more power it develops! Eventually, both header pipes will then develop the same color, and the same length of the blue color, down each pipe.
