Re: Carb "Water Valve" Help Request

[jlandry@domain.elided (John A. Landry)]

When the truth serum kicked in, alice@domain.elided blurted out...

>This is a bit off topic.  My Scout has at least one "water valve" 
>screwed into the intake manifold.  I have never really understood 
>what this does, why it is needed, etc....
[snip]

Mark,

What you describe sounds like a temperature controlled vacuum valve.  What it
does is either allow vacuum to pass when the coolant temp in the manifold
rises above a certain level *or* possibly the exact opposite - shut vacuum off
above a certain temperature.  Some devices such as this have several nipples,
and in that case they usually incorporate several valves - one or more
restricting vacuum on temp rise while at the same time others opening the
vacuum signal on temp rise.

In your case, it sounds like vacuum line from the base of the carb draws the
accumulated gasoline vapors from the carbon canister only if the valve is open
when the manifold temperature is hot enough.  This is very common.  When an
engine is cold (cool manifold) it needs a richer air / fuel mixture to run
properly.  Diluting the air / fuel mixture with extra air being drawn off the
carbon vapor canister would make a cold engine run even worse, so the intend
of the thermostatic valve is to prevent this.  When the engine is warmed up,
the extra dilution of the air / fuel mixture is not a problem (and is likely
compensated for by carb jetting, etc.).

Simply bypassing the valve *could* result in a rougher running cold engine
(until warmed up).  Removing the vacuum line to the carbon vapor canister
altogether will result in increased unburned fuel vapors escaping into and
polluting the atmosphere *and* it could result in the engine running richer
when warmed, possibly leading to increased fuel consumption and greater
exhaust pollution.

Regards,

John
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