Sounds like you've already gotten a few responses but...
(This gets long)
Carbs usually don't go out of adjustment all of a sudden and when something
happens, it usually happens to only one carb, not both at the same time, so
you have symptoms like fouling on only 2 plugs. Possible carb problems that
fit the description are stuck chokes - this can happen to both carbs
suddenly. If the chokes are stuck, reach under each carb and press up on
the nozzle - the lowest part of the carb with the fuel hose on it that
connects to the float chamber. WD40 or carb cleaner can help to unstick the
chokes but often it takes disassembling the carb (if it's really the choke
that is sticking and not the cable or the linkage)
Other possibilities are stuck open float valves or sinking floats. You
would likely have fuel pouring from the overflows on the float chambers.
This is unlikely to occur on both carbs at once. The opposite problem is
what happens on both carbs. If the car is not driven, the fuel varnishes in
the float chamber and causes the needle valves to stick closed. That would
cause the car not to run - no fuel.
After you check the chokes, the next thing to do with any suspected carb
problem is to check the distributor - that's the usual culprit.
You can get the timing out of adjustment or the points burned or an advance
mechanism stuck, or broken advance spring, which would cause poor running
and could cause fouling on all the plugs all of a sudden. Check that the
timing is set properly at idle and then check that it advances properly. As
you rev the engine while running the timing light you'll see the timing
marks move. If you need to you can "add timing marks" to the crank pulley
using paint or a paint marker. Turn the pulley so that you can see the
marks (I think it's easier to do this from under the car) and measure the
space between the marks. That distance is 5 degrees. just paint small
marks on the pulley that same distance apart up to 30 or 35 degrees so that
you've got a better reference when using the timing light.
If your not seeing proper timing or advance - fix that first. Don't forget
to check the points and remember that the condensor can fail and cause some
odd running faults that are very hard to trace. It's not a bad idea to
replace the condensor whenever you replace the points.
Hope that helps,
Brian
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