|
You're talking about the primary and secondary trottles on the carb.
The primary (smaller) throttle plate is directly linked to the accelerator pedal. The more you press your foot, the wider it opens. More open means more air.
The secondary (larger) throttle plate is controlled by that big mushroom at the back of the carb. Its diaphram is controlled by vacuum. You don't see the vacuum passages, since they're inside the carb. The mushroom is held down with three screws. Buried in there is the vacuum passage. The secondary only starts to open as the car is running pretty hot & heavy.
In all seriousness, assume that that part works, since (1) it doesn't have any affect at idle so it's not in your "critical path" and (2) If it's assembled correctly and the various passages are clean, then, it works.
Now, the foot controls the amount of air that gets in the carb, AND NOTHING ELSE, almost. It also causes the acceleration pump to dump about 1cc of gasoline right down the throat of the primary to help accelerate. All the bores inside the carb are used to route air from the trottle bore into the carb body. The result is changes to the air pressure inside the carb and like a straw inside a milkshake, stuff moves.
There's a lot of science to it, none of which, I particularly ever care about. You can look up the Bernoulli brothers from the late 1700's if you want the real dirt on the principles involved (Daniel Bernoulli to get very particular). For the purposes of the at-home restorer, work primarily with the notion that dirt and lint is bad, as is overtightening, undertightening or in general mis-assembling anything. The little rubber syring used to clean out the noses of little tykes is more than suitable to clean up the little bores of the carbs.
Also, if you check out the section 7-1 of the 108 manual again, you'll notice that it describes most of what I just said with lots more words and in greater detail. They call the primary, stage I. The secondary is stage II in their parlance.
-CTH
|