Robert Weeks described a problem with oil burning moving away from idle. I
agree with the previous post that this is a problem with the PCV system, which
Robert later seemed to indicate is no longer there. IMHO thats the problem. In
'92 I converted a 73 B to the Weber 2bbl carb and manifold setup. Since the 68
to 74 MGBs used a simple PCV system (ie no actual valve at all) consisting of
a hose from the crankcase to each of the carbs, at a point behind the
butterflys, with fresh air from either the filler cap or (on the 18V) from the
valve cover via the charcoal canister. This works as follows:with the throttle
butterflies closed at idle the air velocity is very high and a large negative
pressure (suction) exists just behind the butterflys, which will relieve the
positve pressure in the crankcase. The suction at the point were the hoses
connect to the carbs decreases in relation to the opening of the butterflies,
which results in a very effective PCV system. I was faced with the same
dilemma as Robert: How to vent the crankcase using a different carb setup. If
you dont vent it properly, or adequately, you will definately see oil burning
and seal leakage and as the crankcase pressure builds it WILL vent itself
wherever possible.
My solution back then was to find an old Smiths PCV valve from a pre-68,
which I installed on the Pierce manifold, replacing the diaphram first of
course. I connected this with a hose to crankcase as in the original system.
I had tried various combinations of PCV valves used on Americal cars with
different hose arrangements etc, but came back to the MG engineered setup in
the end. For the fresh air intake I was able to keep the original hose from
the valve cover to the cannister. I had tried a hose from the valve cover to a
fitting in the base plate of air cleaner, but found that the small air cleaner
tended to work against the PCV valve. You want the engine to pull fresh air
from a low pressure (atmospheric) source for best results. If you have no
cannister a large fuel filter will suffice as a breather filter. You may want
to convert your vented oil filler cap to a later type valve cover if you drive
in dusty conditions so that clean FILTERED air is drawn into the engine only.
It worked for me. Hope this helps. Cheers. Andy Blackley
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