To eliminate the distributor as the cause of the problem, take a timing light and note when the
distributor begins to advance. You can easily tell by watching the pulley TDC (top dead center) mark
which should be at the 5 degree advance point at idle. That will be about 1/4" ahead of the top dead
center point if you are working with a light that doesn't give you the angle. If it starts moving at a little
over 1000 rpm, between 980 and 1020, you are okay. You might have someone watch your tach for
you. Do this when engine cold and hot. Take into consideration that your tach might be slightly off, but
look for the distributor to begin to advance in that general 1000 rpm range.
Mechanics seem to have their own favorite way of tuning for idle. Some set the total advance first by
moving the distributor to set the total advance and let the static timing be whatever it turns out to be,
then adjust the mixture and idle screws. This is the 911 approach to timing and incorrect for a 356.
Set the static timing at 5 degrees before top dead center, and then go after the idle mixture and
throttle stops, for proper distributor / carburetor set up.
You should be able to get an idle by setting the static timing to 5 degrees BTD, opening the idle
mixture screws 1 1/4 turns, and opening the butterflies by about .015".
BEFORE YOU START take out the idle mixture screws and see if any of them have the "ham fisted"
groove on the tapered needle. If so, it is worthless and needs replacement before going any further.
Check the idle jets, too, and make sure they are not plugged.
If not, then proceed as follows. With the throttle rods disconnected adjust the throttle stops so that
each carb is pulling the same amount of air. Now adjust the throttle stops so that the engine is idling
below 1000 rpm and they are still pulling the same amount of air. A synchrometer or Unisyn is
needed, the Synchrometer is a little easier to use. Starting with #1 adjust the idle mixture screw so the
highest idle is reached with that screw. Lower the throttle stop if necessary to keep the distributor
from advancing. Do this for #2 through #4. Now do it again. If the idle mixture screws wind up to be
less than one turn out then either your float level is too high or your idle jet is too large. On a Zenith,
suspect the float level. If the idle mixture screw is over two turns out then your idle jet is too small.
Again, on a Zenith, suspect the float level. After all this is done, your float level is correct, and you still
have the problem then worn butterlies are the likely cause.
The idle will pick up after the engine warms up because the fuel mixture is better vaporized. This is
why you do it when the engine is at operating temperature.
But with worn butterflies even more gas mixture is introduced. Next thing to look for is an air leak. This
is found by allowing a flammable gas to areas where gaskets are and listening for an
increase/decrease in idle. Beware of fire! Don't use gasoline, paint thinner, ect. A cigarette lighter
(with no flame, of course) with the propane valve open and pointed in the right direction is a choice.
Nitrogen gas is safe and will reduce the idle because it replaces the oxygen in the air.
You should be able to lift the throttle rods about 3/16" after they are disconnected from the throttle
arms. This allows for the expansion of the whole throttle linkage after it warms up. The engine