>>> "A vented cap elimates....."
I know, David. Which is why I am confused as your prior post (sent in
separate off-list email on the way to you) mentioning the need for a
"vented" cap with this system seems contra-indicated to me, also.
>>> BTW....I do not have a schematic for the closed loop fuel system so I
>>> haven't got the information I need, with expansion tank and one-way
>>> check valves, etc. to really "follow" it.
In my RWA Midgets, there were originally three emissions systems.
The air pump sucked hp out of the engine in order to pump air into the
exhaust system so that the combustion process could continue and help
eliminate un-burned hydrocarbons. This was missing from every Midget I have
ever owned. This had the only one-way valve of the entire setup; it was
between the air pump and the head to prevent exhaust d\gases from finding
their way back to the air pump and ruining it. Most air pumps fell victim to
this shortly after the valve died.
A second system scavenges blowby via applying vacuum from the carbs to the
timing chain cover with a metered orrifice on the valve cover connected to
the charcoal cannister. By the time of the RWA models, there was no longer a
PCV valve involved.
The third system was for keeping the raw fuel fumes from the float bowls
from venting to atmosphere. This required a special float chamber cover for
both carbs with an additional take-off on each which was routed to the
charcoal cannister. The third connection to the top of the cannister went
back to the separation tank in the boot and thence to the gas tank. With the
non-vented cap, the depletion of fuel in the gas tank from actually burning
the stuff in the engine sucked fumes from the float bowls back to the
separation chamber where they collected and ran back into the tank as fuel.
Good theory anyway. In the real world, the integrity of the hoses is seldom
intact, especially the ones in the boot which perish inside the woven
covers. A nicely perished hose will frequently allow enough air out to
prevent the cut-off of the gas pump at the station to function, resulting in
copious quantities of spilled fuel.
The bottom of the charcoal cannister was vented to atmosphere as an air
intake so that no vacuum would actually accumulate in the system. There was
a primitive one-way valve for that. The charcoal itself was intended to
absorb vapors when the car had been turned off and release them to their
proper destination when it was started again.
In theory, the charcoal cannister being the only common connection between
these two systems, either one could run separately, provided the other
connection to the cannister were properly blocked. In practise, the air pump
was completely independant and rarely lasted long enough to be functional
when it arrived in the hands of the second owner, and the rest of the
systems were marginal at best. Since I have installed older HS2 carbs
without the angled hoses (I needed the ported vacuum signal), I have elected
to vent the timing chain cover to atmosphere via a hose over the top of the
engine and down into the slip-stream under the car. I also have a vlave
cover with the orrifice surgically removed which is also vented down beside
the other hose. At that juncture I decided to allow the float chambers to
continue to vent to the probably useless cannister with no harm done.
The reason my siggy indicated that I now have a vented cap is that I decided
NOT to retain the vestiges of the non-functional system.