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Stromberg Page 5 - Go to page one two three four five What exactly are Temperature Compensators? To paraphrase the Haynes 'Zenith-Stromberg CD Carburettor' owners workshop manual: "The temperature compensator (TC) is a rectangular housing with a plastic cover that contains a shaped bi-metallic strip, one end is secured to the housing with a screw or rivet, and an adjusting nut is located part-way along its length. The other end of the strip engages a plastic plunger with a conical end which slides in a cylindrical extension of the housing and thus forms a regulating valve. Changes in temperature causes the bi-metallic strip to flex, moving the plunger in its bore, regulating the annular area around the bore thus controlling the amount of by-pass air that is allowed into the carburetors mixing chamber." A common problem with the TC's is that the plastic cylindrical plunger becomes stuck, either open or closed due to build-up of gunk. There is also a rubber or fibre washer that swells with age and can partially (sometimes totally) block the air-bleed. When this happens the owner usually pulls the TC's apart, removes the bi-metallic strip, cleans off the gunk and puts it back together again. However in doing so, you must remove the adjusting nut, and unless you knew that the middle nut was an adjustment.....you were doomed. The specifications on how to adjust the TC's were a closely guarded secret at the Zenith Carburettor factory and were never revealed to any known, living person! The following is the procedure I used on my 1974 1/2 model TR-6, fitted with Zenith-Stromberg 175CD-SEVX carburetors. I image the procedure to be identical for any ZS carburettor fitted with TC's. First remove the bi-metallic strips. At room temperature they should be straight, however you may find yours bent because the DPO screwed down the nylock adjusting nut too much and bent them. After straightening, put them back together and gently tighten the adjusting nut until the plastic plunger just seals the opening in the cylindrical extension of the TC housing, then tighten it one more turn. You now need to 'balance' (if you have multiple carb's) and adjust the opening rate of the plastic plunger. (see my way below, but read through this first - Paul.) This will take some trial and error, but will be worth the trouble. Fill a pan with water, put it on the stove, and place the TC's in the pan so they are completely covered in water and position them so you can observe the opening and closing of the plunger(s) together. Place a cooking thermometer in the water. Turn on the burner real low and observe what temperature the TC's start to open. Based on much experimentation, I found that the plunger should not start to open until around 115F; at 125F it should be about half open, and at 140F the plunger should be fully open. This will introduce a fair amount of 'bypass' air into the mixing chamber when the ambient temperature is fairly warm (90F plus) - probably having to due with decreased air density as well. These should be taken as rough approximations at best, with probably a good 10F - 15F leeway. My experiments took into account cold starting, warm starting, carb needle adjustments (not being fully lean or rich), and general driveability for both in town and open road conditions. When you have the TC's in the pan on the stove, keep a close eye on the water temp. If you need to adjust them, and you will, simply take them out of the water, run some cold tap water over them to cool them down, make the adjustment and put them back in the pan. They react very fast. To make the TC's open at a higher temperature, tighten the adjusting nut - about a 1/2 turn at a time. Most importantly you want the TC's to be balanced, i.e. open and close together at the same temperature. After they are adjusted, put a drop of loctite on the exposed threads of the adjusting nut to keep the nut from moving. Don't move the nut, the loctite will 'seep' down into the nut enough to hold it. Also, check to make sure that the rubber sealing ring in the carburettor body that the nose of the TC's press up against is indeed there and in good shape. Same for the O-ring that goes around the 'snout' of the TC's and presses up against the outside of the carb body. If any of these are missing or cracked you will end up with a major air leak. Some symptoms I have observed from not having enough bypass air is generally good driveability when cold and poor driveability when warm (if EVERYTHING else is in working order - ignition, timing, compression, etc) . Also overly rich mixture only when warm, difficult warm starting and needle mixture adjustment ineffective only when warm. I also had the opportunity to test two brand new, unopened TC's that I came across. The two TC's opening/closing characteristics closely approximated my revised findings, however I was surprised (although not very) to observe a 20F - 25F variance in the opening/closing characteristics of these two TC's. Production tolerance? However, based upon my testing, I believe that the most important operating parameter when dealing with TC's on a multi carb engine is to BALANCE the opening/closing temps and not the absolute temp that the TC's open or close. Several performance articles I have read said to leave the TC's intact as they are necessary for the correct operation of the carburettors. I believe it, as I tried sealing off the TC's and ended up with driveability and hesitation problems on my TR when it was warm. After making the above adjustments, my TR has never run better. But remember, your mileage may vary! *Gunson Colourtune* Setting the air-fuel mixture using a Colortune involves replacing the spark plug in one of the cylinders with the special Colortune plug. The Colortune plug has a transparent window that allows you to see the flame color in the cylinder as it fires. An overly rich mixture will have a yellow flame and will be accompanied by black smoke (and noxious fumes) from the tailpipes. As you lean it out to the optimum stoichiometric mixture, the flame color will change to Bunsen blue. A mixture that is too lean will still have a blue flame, but the brightness will decrease as the mixture is weakened. If the piston dampers in each carb are working correctly, you should see the flame color change from blue to yellow when you open the throttle, and then change back to blue as the engine comes up to speed. Read the Colortune instruction sheet for full details on how the system works. In order to set the air-fuel ratio correctly, you need to know which carburetor feeds which cylinder before you can start making adjustments. In this section, all references to "right" or "left" are made when sitting in the driver's seat looking toward the front of the car. When all the above repairs and adjustments have been made, it’s not a bad idea to re-check the air-flow with the Unisyn or Gunson Carbalancer again. Carb's are like that, but once set up can run for years without problems. END OF ARTICLE BY: Scott Fisher, Roger Garnett, Ken Streeter, Steve Sutton, and other contributors. Late Addition From Dan Siegel (SIII E-type Owner) Re: Flooding Strombergs. This is what I did and it eventually worked for me. Let me say first, that you cannot use the factory float settings as set in stone. I say this because I found the the height of the needle shut-off valve {that I replaced} was not the same height as the original one. Remove carb, drain the fuel, remove float cover. Since the carb is still leaking fuel, I would re-adjust the float height ever so slightly. I would then attach an electric fuel pump with a benign fluid {I used windshield washer fluid} to the inlet side of the carb. I used a 5 psi pump [which is slightly higher psi that needed} and let the pump run for a 1/2 hour or so. If you are still experiencing leakage, you again need to re-adjust the float height so it closes earlier. If after all this is not successful, I would most likely ship off the carb to someone professional like Joe Curto. If you want to just test whether or not the float valve is even shutting off the fuel, you can perform a similar bench test as follows: Remove the float cover. Turn the carb upside down. Turn on the fuel pump with the same windhsield washser fluid, and observe if the needle valve is allowing any fluid past it's seat. The carb must be level. How I balanced the TC valves by Paul This is all about air-flow through the valve and when it opens to allow the air to flow. I wondered if I could work something more precise to balance the flow through each of the temp compensator valves on my Daimler V12's four carburettors. It's nearly four years ago that I did this so use it as a guide and be prepared to experiment. I started by adjusting the bi-metal strip so it was just open in a large bowl of warm water. I placed a thermometer in the bowl to keep a check on temperature. With a short piece of hosepipe and a funnel fitted to the “nose” of the valve housing, I used a stopwatch and timed how long it took for 1 pint of warm water from the bowl to flow through. I kept the valve's bi-metal strip just below the surface of the bowl of water. I adjusted each valve to give the same flow time. The actual temperature isn’t critical, as long as it is warm enough for the valve to be slightly open to allow water to flow. As this takes time, it's important to keep and eye on the thermometer in the bowl and kept it at the same temp for each of the four valves. Then it was just a case of turning the adjustment screw on each by the same amount to produce opening of the valves at temperatures in the above article. I'm writing from memory here, but I adjusted mine to open at a slightly lower temp than the author to allow for the extreme heat build up in the V12 engine compartment. I then repeated the flow test using a bowl of water at a higher temperature as a check. It worked perfectly. All four valves let the water flow through at the same rate. If they hadn't, I would have suspected a fatigued or bent bi-metal strip. Using a Colourtune plug I also used the Colourtune as described to check the mixture. I was actually holding the engine up to 4000 rpm. whilst doing this. BUT YOU MUST USE A MIRROR to check the colour of the flame. If the core of the plug gave way at that engine speed, or indeed any speed, it will be worse than a bullet, so make sure NOTHING is in it's path and wear safety goggles. If anyone reading this wants an "easier-to-access" version of the last few pages with even more photos, go to my "Downloads" page and get the Buckeye Stromberg Word document. However, some content of the "Stromberg Pages" of the web site is not included in that document (eg. my method of balancing the temp compensators), so use the two together. Stromberg Page 5 - Go to page one two three four five This site is for the benefit of enthusiasts. Much of the content is my own to use as you wish. However, some I have collected from various (forgotten) sources in the public domain. If you are the owner of any material used and wish it to be removed or so accredited, please contact me. Web Site © Double Six Design

Stromberg Page 5 - Go to page one two three four five

What exactly are Temperature Compensators?

To paraphrase the Haynes 'Zenith-Stromberg CD Carburettor' owners workshop manual:

"The temperature compensator (TC) is a rectangular housing with a plastic cover that contains a shaped bi-metallic strip, one end is secured to the housing with a screw or rivet, and an adjusting nut is located part-way along its length. The other end of the strip engages a plastic plunger with a conical end which slides in a cylindrical extension of the housing and thus forms a regulating valve.

Changes in temperature causes the bi-metallic strip to flex, moving the plunger in its bore, regulating the annular area around the bore thus controlling the amount of by-pass air that is allowed into the carburetors mixing chamber."

A common problem with the TC's is that the plastic cylindrical plunger becomes stuck, either open or closed due to build-up of gunk. There is also a rubber or fibre washer that swells with age and can partially (sometimes totally) block the air-bleed. When this happens the owner usually pulls the TC's apart, removes the bi-metallic strip, cleans off the gunk and puts it back together again. However in doing so, you must remove the adjusting nut, and unless you knew that the middle nut was an adjustment.....you were doomed.

The specifications on how to adjust the TC's were a closely guarded secret at the Zenith Carburettor factory and were never revealed to any known, living person!

The following is the procedure I used on my 1974 1/2 model TR-6, fitted with Zenith-Stromberg 175CD-SEVX carburetors. I image the procedure to be identical for any ZS carburettor fitted with TC's.

First remove the bi-metallic strips. At room temperature they should be straight, however you may find yours bent because the DPO screwed down the nylock adjusting nut too much and bent them. After straightening, put them back together and gently tighten the adjusting nut until the plastic plunger just seals the opening in the cylindrical extension of the TC housing, then tighten it one more turn.

You now need to 'balance' (if you have multiple carb's) and adjust the opening rate of the plastic plunger. (see my way below, but read through this first - Paul.) This will take some trial and error, but will be worth the trouble. Fill a pan with water, put it on the stove, and place the TC's in the pan so they are completely covered in water and position them so you can observe the opening and closing of the plunger(s) together. Place a cooking thermometer in the water. Turn on the burner real low and observe what temperature the TC's start to open.

Based on much experimentation, I found that the plunger should not start to open until around 115F; at 125F it should be about half open, and at 140F the plunger should be fully open. This will introduce a fair amount of 'bypass' air into the mixing chamber when the ambient temperature is fairly warm (90F plus) - probably having to due with decreased air density as well. These should be taken as rough approximations at best, with probably a good 10F - 15F leeway. My experiments took into account cold starting, warm starting, carb needle adjustments (not being fully lean or rich), and general driveability for both in town and open road conditions.

When you have the TC's in the pan on the stove, keep a close eye on the water temp. If you need to adjust them, and you will, simply take them out of the water, run some cold tap water over them to cool them down, make the adjustment and put them back in the pan. They react very fast. To make the TC's open at a higher temperature, tighten the adjusting nut - about a 1/2 turn at a time. Most importantly you want the TC's to be balanced, i.e. open and close together at the same temperature.

After they are adjusted, put a drop of loctite on the exposed threads of the adjusting nut to keep the nut from moving. Don't move the nut, the loctite will 'seep' down into the nut enough to hold it. Also, check to make sure that the rubber sealing ring in the carburettor body that the nose of the TC's press up against is indeed there and in good shape. Same for the O-ring that goes around the 'snout' of the TC's and presses up against the outside of the carb body. If any of these are missing or cracked you will end up with a major air leak.

Some symptoms I have observed from not having enough bypass air is generally good driveability when cold and poor driveability when warm (if EVERYTHING else is in working order - ignition, timing, compression, etc) . Also overly rich mixture only when warm, difficult warm starting and needle mixture adjustment ineffective only when warm.

I also had the opportunity to test two brand new, unopened TC's that I came across. The two TC's opening/closing characteristics closely approximated my revised findings, however I was surprised (although not very) to observe a 20F - 25F variance in the opening/closing characteristics of these two TC's. Production tolerance?

However, based upon my testing, I believe that the most important operating parameter when dealing with TC's on a multi carb engine is to BALANCE the opening/closing temps and not the absolute temp that the TC's open or close.

Several performance articles I have read said to leave the TC's intact as they are necessary for the correct operation of the carburettors. I believe it, as I tried sealing off the TC's and ended up with driveability and hesitation problems on my TR when it was warm.

After making the above adjustments, my TR has never run better. But remember, your mileage may vary!

Gunson Colourtune

Setting the air-fuel mixture using a Colortune involves replacing the spark plug in one of the cylinders with the special Colortune plug. The Colortune plug has a transparent window that allows you to see the flame color in the cylinder as it fires. An overly rich mixture will have a yellow flame and will be accompanied by black smoke (and noxious fumes) from the tailpipes. As you lean it out to the optimum stoichiometric mixture, the flame color will change to Bunsen blue. A mixture that is too lean will still have a blue flame, but the brightness will decrease as the mixture is weakened. If the piston dampers in each carb are working correctly, you should see the flame color change from blue to yellow when you open the throttle, and then change back to blue as the engine comes up to speed. Read the Colortune instruction sheet for full details on how the system works.

In order to set the air-fuel ratio correctly, you need to know which carburetor feeds which cylinder before you can start making adjustments. In this section, all references to "right" or "left" are made when sitting in the driver's seat looking toward the front of the car.

When all the above repairs and adjustments have been made, it’s not a bad idea to re-check the air-flow with the Unisyn or Gunson Carbalancer again. Carb's are like that, but once set up can run for years without problems.

END OF ARTICLE BY: Scott Fisher, Roger Garnett, Ken Streeter, Steve Sutton, and other contributors.

Late Addition

From Dan Siegel (SIII E-type Owner) Re: Flooding Strombergs.

This is what I did and it eventually worked for me. Let me say first, that you cannot use the factory float settings as set in stone. I say this because I found the the height of the needle shut-off valve {that I replaced} was not the same height as the original one.

Remove carb, drain the fuel, remove float cover. Since the carb is still leaking fuel, I would re-adjust the float height ever so slightly.

I would then attach an electric fuel pump with a benign fluid {I used windshield washer fluid} to the inlet side of the carb. I used a 5 psi pump [which is slightly higher psi that needed} and let the pump run for a 1/2 hour or so. If you are still experiencing leakage, you again need to re-adjust the float height so it closes earlier.

If after all this is not successful, I would most likely ship off the carb to someone professional like Joe Curto. If you want to just test whether or not the float valve is even shutting off the fuel, you can perform a similar bench test as follows:

Remove the float cover. Turn the carb upside down. Turn on the fuel pump with the same windhsield washser fluid, and observe if the needle valve is allowing any fluid past it's seat. The carb must be level.

How I balanced the TC valves by Paul

This is all about air-flow through the valve and when it opens to allow the air to flow. I wondered if I could work something more precise to balance the flow through each of the temp compensator valves on my Daimler V12's four carburettors.

It's nearly four years ago that I did this so use it as a guide and be prepared to experiment. I started by adjusting the bi-metal strip so it was just open in a large bowl of warm water. I placed a thermometer in the bowl to keep a check on temperature. With a short piece of hosepipe and a funnel fitted to the “nose” of the valve housing, I used a stopwatch and timed how long it took for 1 pint of warm water from the bowl to flow through. I kept the valve's bi-metal strip just below the surface of the bowl of water. I adjusted each valve to give the same flow time. The actual temperature isn’t critical, as long as it is warm enough for the valve to be slightly open to allow water to flow.

As this takes time, it's important to keep and eye on the thermometer in the bowl and kept it at the same temp for each of the four valves. Then it was just a case of turning the adjustment screw on each by the same amount to produce opening of the valves at temperatures in the above article.

I'm writing from memory here, but I adjusted mine to open at a slightly lower temp than the author to allow for the extreme heat build up in the V12 engine compartment. I then repeated the flow test using a bowl of water at a higher temperature as a check. It worked perfectly. All four valves let the water flow through at the same rate. If they hadn't, I would have suspected a fatigued or bent bi-metal strip.

Using a Colourtune plug

I also used the Colourtune as described to check the mixture. I was actually holding the engine up to 4000 rpm. whilst doing this. BUT YOU MUST USE A MIRROR to check the colour of the flame. If the core of the plug gave way at that engine speed, or indeed any speed, it will be worse than a bullet, so make sure NOTHING is in it's path and wear safety goggles.

If anyone reading this wants an "easier-to-access" version of the last few pages with even more photos, go to my "Downloads" page and get the Buckeye Stromberg Word document. However, some content of the "Stromberg Pages" of the web site is not included in that document (eg. my method of balancing the temp compensators), so use the two together.

Stromberg Page 5 - Go to page one two three four five

This site is for the benefit of enthusiasts. Much of the content is my own to use as you wish. However, some I have collected from various (forgotten) sources in the public domain. If you are the owner of any material used and wish it to be removed or so accredited, please contact me.