The Zenith Stromberg Carburetor Saga, (again)
Posted: 15 Mar 2008 17:08
I became aware of this website whilst sorting thru the effects of my late nephew, as he visited this site frequently. He, and I, and his cousins interacted on various problems we all encountered on our TR7's, and took the time to compose the experiences, just as I taught all my students over the years. One of the experiences we shared was the adjusting of the fuel system and carburetion.
Prior to any tinkering with the Z-S carburetors, one MUST examine and ensure the proper conditon of the compression AND the ignition componets. This means the spark plugs must be cleaned and gapped. The spark plugs wires have no breaks or current leakage. The rotor and distributor cap contacts cleaned and not damaged. The coil is putting out it's proper voltage at all RPM's. Also, the fuel pump must be functioning correctly and the fuel filter(s) are not clogged.
All vacuum lines must be in good condition including the vacuum lines behind the panel in the trunk under the gas cap. The pre-heater hose from the exhaust manifold to the air cleaner must be in good condition. This is especially important in cold climates as the Z-S units are designed to function best when they are at a temperature of about 100 degrees F. Once these steps are done, one will need a few important tools.
The special tools for adjusting the Z-S carburetors are few, yet vital. To adjust the mixture, a long handle 3/16" hex wrench and a extra large common screwdiver are needed. Or, one can order the special made adjusting tool from Vict Brit for about $9.95. Then there is the balancing tool. A rubber hose in your ear is effective, or order from Vict Brit the synchronizer tool for about $34.95 as is noted in this Spring 2007 catalog. As for determing the correct mixture for combustion, Vict Brit will sell you the Colortune kit for about $69.95, or you can become adept at pulling the #2 and #3 spark plugs to find the preferred light tan color of the insulator nose down to it's base. As you can see, there are two ways to deal with ones tool needs, the expensive way and the thrifty way. Both ways are equally effective. The Haynes Publishing Group puts out a Z-S CD Carburetor Owners Workshop Manual that makes for good reading. The fuel section in the factory workshop manual is also illuminating, as are the exploded parts sections in the various parts catalogs. Let us also not forget the various websites dealing with the Z-S units. These carburetors were used on many different models of cars.
To start with, what are the color of your spark plugs? Are they all a light tan or are they caked in a dry black soot? Are they dripping with oil? Are they bleached white? Are they all the same color? The color we seek is for all to be a light, clean, tan. The mixture is controlled primarily by the needle that is attached to the piston/diaphragm assembly. It is accessed by removing the four screws in the top chamber of the unit. Set aside the screws, lift off the chamber noting how it was installed, then pull out the spring. With rag in hand, lift away the piston/diaphagm assembly and place it on clean newspaper on your workbench. There will be a slight drippage of oil/gasoline from the inside.
Examine the needle. It should not be bent. It should not be gouged. It will probaly be caked with evaporated gasoline deposits if the car has not been used on a regular basis. Remove the deposits with fine sandpaper taking care not to gouge the shank. Examine the rubber diaphrgm for cracking, tears, or holes. Manipulate the rubber thoroughly, if any holes appear, install a new diaphragm. Of note, with the ever changing nature of motor fuels and the introduction of various alcohols into the mix, expect to replace your diaphragm on a more frequent schedule as they deteriorate. There is also a small O-ring that seals the needle assmbly in the stalk of the piston. If you must frequently add oil to the stalk, that O-ring has perished. This is common and many let it go and just add a squirt of oil as needed. Reinstall the piston assembly in the reverse order noting the rubber tang on the diaphragm goes in the slot in the carb body.
Remove the air cleaner assembly. Is your air filter dirty? Replace it as needed. Clean out the inside of the air cleaner and set it aside. Remove the six 1/2" bolts and the inner air cleaner assembly. At this point, we will check the float levels. Using a 1/4" drive ratchet with a socket to fit a screwdriver bit, remove the six screws from the bottom of the float bowl. Yes, we are leaving the carburetor bodies mounted in place. The back center screw is the hard one, use the bit and an approprite open end wrench to access it. This is done by braille. Once the screws are out, jiggle off the bowl as gently as possible as gasoline will spill. Do not worry about the gasket. With the bowl on the work bench, clean the accumulation of deposits from the bowl. This is why the fuel filters are so important. Remove the float needle and confirm it rattles up and down freely. Remove and clean the float noting the flat side goes down. Using a razor blade clean away the gasket remains from the float bowl and the underside of the body. Using a pane of glass and a sheet of very fine sandpaper, grind flat the float bowl flange to ensure a leak free surface. This is a soft aluminium and needs little pressure. Reassemble the float needle and float. To check the float level, use a small 6" ruler to measure the distance from the body to the float bottom. The factory calls for 5/8". We have set ours at 11/16" with no ill effect. Bend the float tab, keeping it level to achieve the setting desired. Note this is all done with your head upside down, so maintain your perspective. Reinstall the float bowl with a new gasket. Move on to the the next carburetor and repeat the process.
Now we come to the tuning phase. Start the car and let it warm up. As noted above, the carburetors function best at a temperature of about 100 degrees F. While waiting, check your float bowls for leaks. Stop the engine and remedy any leaks immediately. We do not use any sealants on our gaskets as the correct fuel level keeps the fuel below the gasket line. If you have an infrared temperature gun, observe the carburetor temperature rise along with the upper radiator hose and thermostat housing temperatures. Without the tempertaure gun, feel the upper radiator hose getting hot and note the inside temperature gauge rising to it's normal operating range.
With the hose in your ear or the synchronizer tool in hand, listen/see how the rear carburtor is hissing/the tool's float ball has risen. Remembering this, do the same on the front carburetor. Are they both the same? Recheck both units. If they are not, adjust the idle adjusting screw on the left side of the carburetors to balance the air flow for a steady idle of about 800 RPM. Recheck again. Rev up the speed and hold it there for a brief period to clear the intake tract and recheck idle speed and balance again. This sets the idle.
To synchronize the units when accelerating, there is a balance bar with two adjusting screws. The factory manual says to set the clearance at .010". These screws are not for setting the idle, they are for syncronizing the carburetors. Raise the RPM from 800 to 1600 and check the air flow balance. Adjust these screws to achieve a balance.
Now we come to the mixture. If the sparkplugs continue to display a light tan, you're okay. If not, the adusting tool is fitted thru top of the carburetor, down the stalk to fit in the hex nut. Rotate the wrench clockwise to richen and counter-clockwise to lean while holding the piston from rotating with the large screwdiver if you do not have the mixture tool. Turn the wrench in small amounts and check the mixture. Those with a Colortune will see this happen imediately or if you are so lucky to have a exhaust analyzer, the same. For those without, drive the car for a while and check the spark plug color until the light tan is achieved. Then recheck the air flow balance. The original factory setting for the CO level is shown on the sticker on the underside of the hood.
However, after all these years, it is doubtful they can meet those emission standards due to wear of the various componets such as the piston to bore, the needle and it's bore, the throttle shaft and it's bushing. The best we can do is dial in as best we can for smooth running and economy of operation.
The parts commonly needed for this excercise are two float bowl gaskets, the diaphragms, and the tools. They can be found from all the major and most minor vendors. Victoria British supplies a free catalog and has online service. TRF is online, as is British parts Northwest. A common question is the kind of oil used in the needle stalk. Many opinions are out there and we have used a wide variety of oils over the years ranging from engine oil to Marvel Mystery oil to gun oil to sewing machine oil. We cannot detect any difference in how the piston rises in our use of the cars.
Mildred Hargis
Prior to any tinkering with the Z-S carburetors, one MUST examine and ensure the proper conditon of the compression AND the ignition componets. This means the spark plugs must be cleaned and gapped. The spark plugs wires have no breaks or current leakage. The rotor and distributor cap contacts cleaned and not damaged. The coil is putting out it's proper voltage at all RPM's. Also, the fuel pump must be functioning correctly and the fuel filter(s) are not clogged.
All vacuum lines must be in good condition including the vacuum lines behind the panel in the trunk under the gas cap. The pre-heater hose from the exhaust manifold to the air cleaner must be in good condition. This is especially important in cold climates as the Z-S units are designed to function best when they are at a temperature of about 100 degrees F. Once these steps are done, one will need a few important tools.
The special tools for adjusting the Z-S carburetors are few, yet vital. To adjust the mixture, a long handle 3/16" hex wrench and a extra large common screwdiver are needed. Or, one can order the special made adjusting tool from Vict Brit for about $9.95. Then there is the balancing tool. A rubber hose in your ear is effective, or order from Vict Brit the synchronizer tool for about $34.95 as is noted in this Spring 2007 catalog. As for determing the correct mixture for combustion, Vict Brit will sell you the Colortune kit for about $69.95, or you can become adept at pulling the #2 and #3 spark plugs to find the preferred light tan color of the insulator nose down to it's base. As you can see, there are two ways to deal with ones tool needs, the expensive way and the thrifty way. Both ways are equally effective. The Haynes Publishing Group puts out a Z-S CD Carburetor Owners Workshop Manual that makes for good reading. The fuel section in the factory workshop manual is also illuminating, as are the exploded parts sections in the various parts catalogs. Let us also not forget the various websites dealing with the Z-S units. These carburetors were used on many different models of cars.
To start with, what are the color of your spark plugs? Are they all a light tan or are they caked in a dry black soot? Are they dripping with oil? Are they bleached white? Are they all the same color? The color we seek is for all to be a light, clean, tan. The mixture is controlled primarily by the needle that is attached to the piston/diaphragm assembly. It is accessed by removing the four screws in the top chamber of the unit. Set aside the screws, lift off the chamber noting how it was installed, then pull out the spring. With rag in hand, lift away the piston/diaphagm assembly and place it on clean newspaper on your workbench. There will be a slight drippage of oil/gasoline from the inside.
Examine the needle. It should not be bent. It should not be gouged. It will probaly be caked with evaporated gasoline deposits if the car has not been used on a regular basis. Remove the deposits with fine sandpaper taking care not to gouge the shank. Examine the rubber diaphrgm for cracking, tears, or holes. Manipulate the rubber thoroughly, if any holes appear, install a new diaphragm. Of note, with the ever changing nature of motor fuels and the introduction of various alcohols into the mix, expect to replace your diaphragm on a more frequent schedule as they deteriorate. There is also a small O-ring that seals the needle assmbly in the stalk of the piston. If you must frequently add oil to the stalk, that O-ring has perished. This is common and many let it go and just add a squirt of oil as needed. Reinstall the piston assembly in the reverse order noting the rubber tang on the diaphragm goes in the slot in the carb body.
Remove the air cleaner assembly. Is your air filter dirty? Replace it as needed. Clean out the inside of the air cleaner and set it aside. Remove the six 1/2" bolts and the inner air cleaner assembly. At this point, we will check the float levels. Using a 1/4" drive ratchet with a socket to fit a screwdriver bit, remove the six screws from the bottom of the float bowl. Yes, we are leaving the carburetor bodies mounted in place. The back center screw is the hard one, use the bit and an approprite open end wrench to access it. This is done by braille. Once the screws are out, jiggle off the bowl as gently as possible as gasoline will spill. Do not worry about the gasket. With the bowl on the work bench, clean the accumulation of deposits from the bowl. This is why the fuel filters are so important. Remove the float needle and confirm it rattles up and down freely. Remove and clean the float noting the flat side goes down. Using a razor blade clean away the gasket remains from the float bowl and the underside of the body. Using a pane of glass and a sheet of very fine sandpaper, grind flat the float bowl flange to ensure a leak free surface. This is a soft aluminium and needs little pressure. Reassemble the float needle and float. To check the float level, use a small 6" ruler to measure the distance from the body to the float bottom. The factory calls for 5/8". We have set ours at 11/16" with no ill effect. Bend the float tab, keeping it level to achieve the setting desired. Note this is all done with your head upside down, so maintain your perspective. Reinstall the float bowl with a new gasket. Move on to the the next carburetor and repeat the process.
Now we come to the tuning phase. Start the car and let it warm up. As noted above, the carburetors function best at a temperature of about 100 degrees F. While waiting, check your float bowls for leaks. Stop the engine and remedy any leaks immediately. We do not use any sealants on our gaskets as the correct fuel level keeps the fuel below the gasket line. If you have an infrared temperature gun, observe the carburetor temperature rise along with the upper radiator hose and thermostat housing temperatures. Without the tempertaure gun, feel the upper radiator hose getting hot and note the inside temperature gauge rising to it's normal operating range.
With the hose in your ear or the synchronizer tool in hand, listen/see how the rear carburtor is hissing/the tool's float ball has risen. Remembering this, do the same on the front carburetor. Are they both the same? Recheck both units. If they are not, adjust the idle adjusting screw on the left side of the carburetors to balance the air flow for a steady idle of about 800 RPM. Recheck again. Rev up the speed and hold it there for a brief period to clear the intake tract and recheck idle speed and balance again. This sets the idle.
To synchronize the units when accelerating, there is a balance bar with two adjusting screws. The factory manual says to set the clearance at .010". These screws are not for setting the idle, they are for syncronizing the carburetors. Raise the RPM from 800 to 1600 and check the air flow balance. Adjust these screws to achieve a balance.
Now we come to the mixture. If the sparkplugs continue to display a light tan, you're okay. If not, the adusting tool is fitted thru top of the carburetor, down the stalk to fit in the hex nut. Rotate the wrench clockwise to richen and counter-clockwise to lean while holding the piston from rotating with the large screwdiver if you do not have the mixture tool. Turn the wrench in small amounts and check the mixture. Those with a Colortune will see this happen imediately or if you are so lucky to have a exhaust analyzer, the same. For those without, drive the car for a while and check the spark plug color until the light tan is achieved. Then recheck the air flow balance. The original factory setting for the CO level is shown on the sticker on the underside of the hood.
However, after all these years, it is doubtful they can meet those emission standards due to wear of the various componets such as the piston to bore, the needle and it's bore, the throttle shaft and it's bushing. The best we can do is dial in as best we can for smooth running and economy of operation.
The parts commonly needed for this excercise are two float bowl gaskets, the diaphragms, and the tools. They can be found from all the major and most minor vendors. Victoria British supplies a free catalog and has online service. TRF is online, as is British parts Northwest. A common question is the kind of oil used in the needle stalk. Many opinions are out there and we have used a wide variety of oils over the years ranging from engine oil to Marvel Mystery oil to gun oil to sewing machine oil. We cannot detect any difference in how the piston rises in our use of the cars.
Mildred Hargis
