Ron:
First of all, let me ask: Is your engine modified? If you have
changed the cam, then engine will be much fussier and VERY sensitive to
vacuum leaks.
In particular, the emissions breather hose from the valve cover to
carbs and carbon canister will be problematic. The stock cam has
terrific vacuum (if somewhat indifferent performance) and will pull the
crankcase blow by and carbon canister vapors without blinking an eye. A
performance cam may well not have enough vacuum to tolerate much blow by
or vapors.
So, the first thing you should do is disconnect your blow by hose
from the carbs and cap the carb fittings. Does this resolve the problem?
If so the you will need to fabricate a restrictor for the hose to limit
(but not eliminate) the flow from the canister and crankcase to the
carbs. Ultimately, this is what I had to do as my cam would just not
tolerate the wide open flow through that hose. If you have studied how
the carbon canister works, you know that it is open to atmosphere and so
there is a lot of air flowing through it when the engine is running.
DON'T cap off the fitting permanently, as the engine will last longer
with the crankcase ventilation working, not to mention stay cleaner.
OK, assuming that item is taken care of or was never an issue, lets
talk about the bypass valves. Yes, the idle is set using the idle screw.
BUT, if misadjusted, the bypass will also affect idle. The bypass is a
controlled leak of air AROUND the air valve (carb piston). Its job is to
spoil the vacuum between the butterfly and air valve. It does this by
opening when manifold vacuum is extremely high (i.e. during
deceleration) and leaks air from the intake side of the carb to between
the air valve and butterfly. The air valve "sees" a much lower vacuum,
and so fully closes to reduce fuel flow. This leans the mixture and
prevents baby seal killing hydrocarbons from polluting the air, and
causing the end of life as we know it.
If the valve is misadjusted, it opens at too low a vacuum (such as
when the car is idling) and acts like a big vacuum leak - causing rough
idle, constipation, liberal politics, heavy metal music and a host of
other evils. When it is properly adjusted it does NOT affect idle, when
it is misadjusted it definitely affects idle.
In your carb2.jpg, the adjuster is labeled "1". In carb1.jpg, the
bypass assembly has been removed from the carb, so the adjustment screw
is not present at all. (Listers will not see the JPGs as the server
removes them)
Make sure the car is fully warmed up, and the choke is fully home
(not pulled out from the dash).
Cap the breather fittings on the carbs. On each carburetor in turn,
turning the bypass adjuster about 2 turns CLOCKWISE should result in a
very noticeable increase in idle speed. If this does NOT happen, the
valve was misadjusted.
Back off each adjuster by turning it COUNTER CLOCKWISE until the
idle falls, then turn it COUNTER CLOCKWISE one turn more. This is the
correct setting for the bypass valve.
If you cannot get the idle speed to rise and then fall by turning
the adjuster then the valve is defective and must be rebuilt. Rebuilding
it is trivial, all you need do is remove the valve (3 screws) and
replace the internal diaphragm (available from moss). Clean the valve
assembly in some lacquer thinner before reinstalling it.
end part 1 ......
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