Zenith Installation instructions
John Jenkins
Please read instructions fully before beginning your installation and
contact us immediately if you have any problems! We can only help
you if parts and and basic settings are the same as when the
carburetors were shipped.  Once things have been changed, we are
no longer responsible! you will also find additional information about
carburetor balancing and engine tuning in an article by Jack Staggs
Your Zeniths from 356 Carb Rescue have their float bowls and injection volumes
already set as per factory specifications. The injection volumes are adjusted
very close to 0.25 cc for two pumps. This volume falls in the middle of the
specifications for Normals and Supers and at the bottom of the specification for
the 356C. Today’s fuel is more volatile so less injection volume is needed. The
idling set screws have been turned in such that the butterflies are open ten
thousandths of an inch. The idle control screws or idle mixture screws are open
1 1/4 turns. This combination assures your engine will operate without the
throttle linkage connected after you fire it up. Note: As of June 2009 our Zeniths
are run on our test engine before shipping. If you receive a set of our Zeniths
after this date they will already be adjusted for idle. All you should have to do is
slightly turn the idle mixture screws in/out to see if your engine idle speed
improves, and slightly adjust the idle set screws for your engine.
Warm the
engine up first before making adjustments.

Important! Before you install the carburetors on your engine be sure the
gasoline supply is free of particles and dirt. The float valves are very sensitive to
particles and will not close properly which will cause the fuel to overflow in the
bowls and flood your engine with gasoline. The setting of the float bowls is done
with paint thinner, the specific gravity of which is very close to gasoline. This
allows us the set the float level accurately and find any sticking float valves due
to the manufacturing process or particles that have found their way into the top
cover of the carburetor. Paint thinner is a lot safer, too. After the carburetor is
set up correctly the paint thinner is removed, the residual blown dry, and then
installed and run on our test engine. While on the test engine we make sure all
the idle mixture screws exhibit correct behavior, i.e., they work, and we adjust
the idle set screws for the appropriate idle speed, e.g., 750 rpm for Normals.
And, we check again for any leaks. FYI, we have found that if the carburetors set
on the shelf for a long period of time (e.g., greater than six months) the float
valve has a tendency to stick. Also, the leather on the accelerator plunger will
shrink and may not push the gas into the injection nozzles. Beginning in June
2009 we now oil the float valve and the leather on the plunger to prevent these
problems. If you need to swell the leather use denatured alcohol. 95 proof, not
rubbing alcohol. Leave it in the alcohol for 15 minutes or so. Most often the float
valve will stick because dirt or particles are introduced into the gas lines after a
restoration or work has been done on the car. We highly recommend a gasoline
filter be installed in your car. Use a metal one and if you want to retain the
originality of the gas lines on the engine then install it underneath the car
somewhere after the gas line exits the tunnel.

Before you start you will need:

-Unisyn or Synchrometer (flow meter)
-9 mm and 10 mm open end wrenches
-flat blade screw driver for idle adjustment and mixture screws
-12 mm box end wrench; short
-(8) 8 mm nuts with 12 mm flats, not 13mm
-(8) 8 mm wave washers
-17 mm open end wrench
-(4) red fiber washers for banjo bolts
-(2) banjo bolts to connect gas lines to carb tops
-(2) carburetor to manifold gaskets
-more than two gallons of gas in your tank

Mount the carbs. A little past snug is enough. No need to tighten the nuts to
100 foot pounds. When you are using your 12 mm wrench to tighten the nuts
be careful not to hit the idle mixture screws and bend them. The one most often
bent is for number one cylinder. This is because it is directly in the path of the
on coming wrench as you tighten the nut close by. Connect the gas lines with
the banjo bolts. Do not try to tighten any more than is necessary. You can strip
the threads. Get one "squeek" out of it and leave it alone until after the car is
running. Check to see then if you need to tighten them any more. Check again
after a day so. The fiber washers will compress. If a slight movement will not
stop the leak then use another red fiber washer rather than over tighten the
banjo bolt. Connect the throttle linkage for each carb so that they are close to
even before you start. Have someone check to make sure the butterflies do not
go past the full open position when the gas pedal is fully depressed. There must
be a clearance of about 1 mm between the throttle stops and abutments on the
carburetor bodies. Also make sure the throttle is not partially open when the
gas pedal is fully depressed. Refer to the manual for the proper setting up of
the linkage starting from the bell crank on the fan shroud to the gas pedal.
Warning – if the linkage does not have a little play or slack in it then you will
have a hard time getting the idle speed down because the butterflies will not be
closing as they should.

Use the starter to begin filling up the carbs with gas. You may have to crank it
for a minute or two. Once you hear the engine fire stop and check for leaks. The
jet covers first and then the banjo bolts.  These two areas are the most likely to
leak. Yes, we check the jet covers when we set them up but check them again to
be safe. Then go down your gas line to make sure there are no leaks in your
hoses or connections.

After all the leaks are repaired then start the engine. Check the banjo bolts
again now that the gasoline pressure is higher. Look down the throat of the
carbs and see if gasoline is leaking out of the bowl into the throat. If you see
gas dripping into the throat then the float is stuck open. Shut it off. Take off
the top of the carb and make sure the float is moving freely. Then check the
float valve to make sure no particles are stuck in the valve. Blow it out well with
compressed air. There are no other reasons for the bowl to overflow. Well,
there is one more. The float can have a leak but we checked them. If you think
the float is leaking then shake it to hear gasoline in it. You can also weigh it.
Each float should weigh about 5.2 grams. After all is OK then warm up the
engine. Don't be afraid to use the idle set screws to keep it running.

Disconnect the throttle linkage at the carburetor levers (L/R) and leave the
throttle linkage (length) adjusting nuts loose. Using your Synchrometer or
Unisyn set the idle set screws such that the engine is running at about 1000
rpm and each carb is flowing equally at the same rpm. Now, one at a time, screw
in the idle mixture or volume screws to just before they seat (engine runs
slower) then run them back to about 1 1/2 turns. (Note: if your set of Zeniths
has already been run on our test engine you will not need to turn them in all the
way. All you need to do is turn them slightly each way to see if you can improve
the idle speed for your engine. They have already worked fine on our test
engine.)If the idle mixture screws do not affect the idle speed of the engine as
you turn them in then check your float level. It is probably too high. Determine if
the float level is correct before you continue. Check the fuel pressure. A high fuel
pressure (e.g., greater than five or six psi)will force the float valve open and
raise your float level. If you are not using new idle mixture screws check to see if
one or more of them has any grooves cut in them from someone turning them
in way too tight, or, if the needle part of the idle mixture screw is a little bent. If
they are not exactly centered then you’ll have little luck getting them in the
correct spot for the proper idle mixture. Turn them a little in and out again until
you find the spot at which the engine is running smoothly and highest rpm. I
watch the synchrometer dial. If you have a timing light that gives you rpm then
good for you. Use it. Do this again for both carbs with the idle screws set so the
idle is at 1000 to 1100 Rpm.  Adjust each idle mixture screw in or out until the
highest rpm is achieved. You will probably need to reset the idle set screws after
you have obtained a higher idle speed with the idle mixture or volume screws.
You need to keep the rpms down so the distributor does not advance. That
really messes you up. After you have gone around the idle mixture screws a
couple of times and are satisfied you have them “just right” then adjust the idle
set screws so that the engine is turning at 750 to 950 rpm. Normals should be
about 750, Supers and C’s 850.  This is a
reiterative process. Do it again. Balance the carbs with your flow meter so they
are drawing air evenly. Reset to your preferred idle speed if necessary. This
should be a real easy process. It only takes us about fifteen minutes on our test
engine to dial in a set of Zeniths…..unless they have a problem. This is why we
now run them on a test engine so you don’t have those elusive problems.

Connect the throttle linkage. Make sure there is no tension on the throttle rods
when connected. Increase and hold the engine speed at about 1500 rpm. A
friend really helps here. I place a short piece of wood against my front seat to
hold the pedal steady while I do this adjustment. The manner is up to you but
the rpm needs to be steady. Moving your flow meter from carb to carb, adjust
the two throttle linkages so that the flow is even for both carburetors. If the
flow changes as you go higher in rpm then chances are good that part of your
throttle linkage is worn. Suspect the pivot ball opening on the driver's side of
the cross shaft that goes across the back of the fan shroud and connects to
both throttle rods. This end tends to wear out first.  Keep them greased well.

If you have difficulty setting the idling mixture correctly then suspect ignition or
mechanical problems. The butterflies in our Zeniths are replaced if they show the
slightest wear. We also make sure the throttle spindles are not twisted so both
butterflies will open and close at the same time. The idle mixture screws, of
course, are new so they are not suspect.

When you are satisfied with the settings take a short trip around the block to
clean it out. Then rev up the engine to 3000 rpm and suddenly release the
throttle. If the engine dies or falters the idling mixture is too rich. Turn the idle
mixture screws in a very little. E.g., an eighth of a turn. You are better to have
the idle mixture a little lean rather than foul plugs over time. If the idle mixture is
too lean you will hear some backfiring. As mentioned above, the injection volume
has been kept low as well to avoid plug fouling.

Happy motoring. Don't hesitate to e-mail or call if you have problems. 928-204-
0507 or 619-224-3566
This is a copy of the instructions that will come with your restored
carburetors.  These carbs have been extensively engine tested  before
shipping, you should really have nothing to do but bolt them on, fill them with
gas, let the gas sit for a while to soak into the leather skirt of the accelerator
pump and start 'er up!  maybe adjust the volume control screws.
 If anything
more than that needs attention, call us.