those will be covered here
On the motor side of the carburetor is the throttle valve (butterfly). Here you can see it in the carb and in the closed position
34-carb engine side.jpg
And here are the components of that. Note that the throttle plate has a small hole in it. This ensures that even if the throttle is fully closed that a small amount of air can still pass through the carburetor. Because of this, depending on the mixture the motor can actually still run with the throttle fully closed
35-throttle plate.jpg
And on this side of the carburetor is the "choke" or engine primer plate. You'll see in the low speed control discussion exactly how this works closing this causes much more fuel to be pulled into the motor
BTW - if you remove the choke shaft, there is a small spring and ball at the bottom of it that acts as a detent. When you remove the shaft those parts will fall out so be ready to capture them. Easy to reinstall.
36-carb intake side.jpg
And here are the choke parts. Again even fully closed there is a small hole to allow some air to move through. This is needed to ensure fuel flow through the fuel control systems.
NOTE: the two small indentations on the choke plate serve as alignment guides for attaching the plate to the shaft. Because of the shape of the venturi of the carburetor, this plate has to align precisely when installed. When the indentations align with the shaft, the plate will be aligned.
37-choke plate.jpg
So in the last section we talked about the main fuel reservoir being filled with fuel. That fuel has to get into the carburetor. Note that there is a low speed and high speed control system visible but they are capped off. If they weren't, the motor could pull unlimited fuel through the ports. In this case it would flood with fuel.
So a more precise way to meter the fuel is needed. That way is implemented in the form of needle valves which can be adjusted to allow a precise amount of fuel being allowed to flow
So the fuel has to get from the reservoir to the control needles. It does this by being pulled through the needle feed housing. This is pressed into the carb body and is not serviceable
38-fuel circuit locations.jpg
It does however contain the small composite plate. Basically it acts as a one way valve by only letting fuel into the needle feed cavity. If you look at the previous photo you can see this plate just inside the needle feed port
39-needle feed plate.jpg
If you remove this (and this was a destructive process) you can see that at the bottom is two ports, one directed to each of the needle valves
40-needle feeds.jpg
If you look into the carb body where the high and low speed needles install, you can see that deep inside there are seats machined into each. This is where the needle valves fit. Also the needle feed ports drop into these cavities on the needle side of the seats so fuel flow control into the rest of the system will be controlled by how open or closed the needles are.
41-needle seats.jpg
Finally, here are the actual metering needles. You can see that the tips fit into the seats inside the carburetor and that they have slightly different shapes which account for different fuel flows
42-needles.jpg
these carburetor components provide very fine control over the amount of fuel entering the fuel feed circuits.
The Low Speed CircuitStatistics: Posted by JRgraham — Tue May 27, 2014 9:27 am
]]>