Ron Brown wrote:
> Some of this is conjecture and some is empirical from working
> on my own peds.
> If your carb is like mine, it does not have a tapered needle
> extending from the bottom of the slide to the "needle jet",
> the opening in the venturi which allows gas/gas air mix into
> the air stream. In the absence of a needle, I do not know
> what to call this jet, so I will call it an atomizer which is
> what it would be called in a "butterfly" type carb such as in
> a car.
the throttle cable comes into the carb on the top. 2 cables actually, one being the choke. THe throttle cable is connected to a slider, (that word seems right, but I actually have no idea what it is...) about the size of a quarter roll of dimes. its hollow, and inside, and sticking out the bottom is a long narrow needle valve. There is a compression 'spring' that holds the needle in the slider. This spring is compressed against the inside surface of the slider. I seem to remember this needle sitting at the bottom of the slider, but it seems possible for it to be set anywhere along the height of the slider, with only a small degree of an ability to stay there, so I set it at the bottom...
does this change your response?
> The purpose of this tapered needle is to regulate the
> available gas/gas air for mixing with the incoming air during
> intermediate throttle openings.
> By the way, I use "gas/gas air" because many carbs have an
> emulsifying tube which mixes a small amount of air with the
> gas as it travels from the main jet to the atomizer. This
> assists in atomizing the fuel into the intake air stream.
> If you are not thoroughly confused yet, consider the
> operation of the carb at full throttle. The venturi size is
> fixed by the diameter of the passage through the carb. The
> main jet and air jet to the emulsifier, if any, are also
> fixed. At some rpm, the velocity of the air through the
> venturi will create enough of a pressure drop to draw just
> enough fuel through the main jet/atomizer to give you a
> perfect mixture. If the rpm increases, the air will flow
> faster, creating a greater pressure drop in the venturi,
> drawing more fuel through the atomizer. This sounds perfect
> except that if diameter of the carb restricts air flow at
> all, because it was designed for optimum flow at lower rpm,
> then the pressure will drop even more at the atomizer. This
> causes too much gas to be mixed with the fuel, essentially a
> "choke" effect. The air cleaner/air box can also contribute
> to this.
> The reason you never have the problem goin up hill is because
> you never attain this "excessive" rpm range.
> If you are still with me, the contributing factors to this
> equation are:
> Diameter of the carb venturi.
> Main jet size.
> Emulsifier air jet size.
> Atomizer jet size.
> Float bowl fuel level.
> Any restrictions to air intake, air box, filter, air
> turbulence around the air box.
> Any restrictions to gas flow, dirty jets, plugged filters,
> float bowl and gas tank vents.
> Any of the components which are sized to regulate flow can be
> adversely affected by over agressive cleaning with hard wire,
> drill bits etc.
> Any air leak in a position to allow more air into the
> mixture, carb to manifold, manifold to block, crankshaft
> Any fuel leak which allows more fuel into the mixture, leaky
> float needle, leaky, stuck or misadjusted enrichener (choke),
> loose main jet.
> As you can see, the opportunities for error are many. Some
> cause the mixture to be more rich, some more lean.
> As we know that you have a too rich problem, there are only
> so many things to look at which we can do something about.
> Main jet size, float level and free air flow are the
> simplest, although it is worth verifying that the enrichener
> is ok and the air passages to the emulsifier are clear. You
> have allready determined that the air filter/air box make no
> difference, although this surprises me. This leaves you with
> the float level and main jet size to check/play with.
> It occurs to me that you should also check that the throttle
> slide is opening all the way when you twist the throttle.
I think so... I remember palying with it when I took the carb apart the first time, and was trying to see how the damn thing worked...
> If you are still awake, I hope this helps.
Ahhhh Auto mechanics in high school comes rushing back.... I rebuilt a carb for my '74 Subaru wagon then... what a mess...this is far simpler!