There are three points to consider, as stated by the Webra factory instructions. There
are plenty of "Internet myths" associated with these points. Let's have a look at them,
shall we ?
To grasp the principle of the TN II carburettor (the most common carb on our r/c engines)
it is important to understand that the:
a. the high speed needle (1) only affects the high speed range
b. the idle needle (2) only affects the idle range
c. the tapered tip of the needle (B) influences the idle range in conjunction with the fuel
supply opening in the spraybar (A).
Let's consider the low speed needle first, and this statement:
Darzeelon:
There is no 'idle range'; only an 'idling speed', which depend on the engine and its adjustment
by the user.
Webra Engines makes two references to an "idle range" in their factory instructions. What is
this "idle range" ? The idle "range" is the portion of the lower speed of the engine that is
"controlled" by the low speed needle...the
taper of the needle being the controlling
part. When the throttle (barrel) of the carb is cut back to an idle, the low speed needle goes
inside the spraybar nozzle. When the LS needle is outside the spraybar, it serves no function.
Only when the LS needle taper comes into the spraybar does it have any effect on the fuel flow.
Let's backtrack for a second, so we can understand what is taking place. When the carb barrel closes,
even if it is closed all the way, there is always a small amount of fuel that flows into the spraybar.
This is to allow fuel through for the idling of the engine. This is by design. There will always be this
trickle of fuel....if there were not, the engine would not have any fuel necessary to have an idle.
To be continued....
