It's good that you have the vacuum in the crankcase. Your removing
the cap showed that the carbs are pulling the vacuum.
If the charcoal cannister is clogged, air can't pass through it. The
vacuum in the engine would be whatever the carbs could pull against the
resistance of the cannister's filter. If it's clogged completely, then no
air could pass through at all and there would be no ventilation through
the engine. If partially clogged, there would be partial flow.
A clogged charcoal cannister would not cause pressure in the engine.
You could have intermittent clogs at the connections. We don't know
the maintenance history of the engine, so it is possible that there are
bits of gooey crud in the hoses and other places.
> I'm curious about something, If the charcoal canister was clogged I
> do not understand how this could lead to excessive crankcase pressure.
> long as the crankcase is under vacuum wouldn't blowby be purged? The
> way I can see that the crankcase would become pressurized is if the
> source was clogged and the canister was clogged.
> Can the vacuum connection at the tappet cover clog intermittently or
> can the vacuum ports at the carbs clog intermittently?
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