John and other listers,
Thank you all for the info on the PCV system, I think I understand it now
(or do I?).
I definitely have vacuum in the crankcase. When I pull the oil filler cap
the engine runs very poorly and acts the same as if I pulled the connection
from the carbs to the to the tappet cover. There is vacuum at the valve
I'm curious about something, If the charcoal canister was clogged I do not
understand how this could lead to excessive crankcase pressure. As long as
the crankcase is under vacuum wouldn't blowby be purged? The only way I can
see that the crankcase would become pressurized is if the vacuum source was
clogged and the canister was clogged.
Does this make sense or am I forgetting something?
Can the vacuum connection at the tappet cover clog intermittently or can the
vacuum ports at the carbs clog intermittently?
Frank, I also have a 73. There is no PCV valve, but air should be drawn
into the engine through the air hose running from the charcoal canister to
the valve cover. Eventually the air is sucked into the carbs through the
hose at the front of the engine tappet cover. Your system should have a NON
vented oil cap.
Here is the test I use. If you DO have a non vented oil cap then with the
engine running you should feel a slight vacuum or sucking at the end of the
hose to the charcoal canister. If there is no vacuum or even back pressure
at the hose, then you have pressure building up in the engine.
Alternatively you could pinch off the air hose from the canister to the
valve cover and remove the oil cap while the engine is running. Place your
hand or a sheet of paper lightly over the oil fill hole, you should feel
light suction or see the paper drawn towards the engine/ valve cover.
I do not know the condition of your engine, but blowby caused by worn piston
rings will create excess pressure in an engine.
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