Temperature Compensators

[Adrian]

When I've started the GT6 its struggled to achieve a nice even running and chugs, almost dying until it is up to temperature. Since upgrading to a club electronic dizzy it starts really well and I've been wondering if it is either the choke or compensators (I maybe stupidly, reversed the gasket to unblank the compensator). Whilst I want to get it sorted I also found the following article on the vintage triumph register which you may know about and have dismissed as poppycock!

Your thoughts would be appreciated.

THE ART OF TEMPERATURE COMPENSATOR ADJUSTMENT

by Steve Sutton, ssutton@ridgecrest.ca.us

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 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 carburettors mixing chamber.”

A common problem with the TC’s is that the plastic cylindrical plunger becomes stuck, either open or closed due to buildup of gunk. 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 carburettors. 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 carbs) and adjust the opening rate of the plastic plunger. 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 NOS TC’s that I came across. The two TC’s opening/closing characteristics closely approximated my revised findings, however I was suprised (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!

Good Luck

 

 

[dougbgt6]

Adrian,

Messing with the compensators is a dodgy business particularly when you start adjusting the bi-metallic strips, "mending to destruction" are the words that come to mind!

A lot on here suggest the best thing for them is to block them off completely. I've replaced the rubber grommets, but that's as far as I'm going to go! 

Another good explanation of how they work is on  https://www.buckeyetriumphs.org/carburetors

Doug

[Pete Lewis]

old and  wonky are best closed to a permanent shut ,

they do or should only open up with high under bonnet temperatures and this increases the idle and weakens the mixture by allowing a small air bleed to bypass the throttle plates 

they are when old normally found to have the small plastic plunger partly open at cold and normal temereatures ,, this you do not want , you cannot set the idle mixture if the air bleed is open 

so remove the small housing and its plastic cover  you can tickle the the plunger to see if its open , note there are two 0 rings to seal the housing to the carb body these need to work or air is sucked in regardless of any setting . to close it  screw the small nut to pressure the plunger down its bore .

the mixture should be no dark art, on CDSE the needle is adjusted by sticking a hex key down the dashpot tube,  the needle has a small delrin washer attached to its upper end this must be flush with the base of the air piston 

if the diaphragm is all baggy  wash with petrol will return it to size , make sure the small locating lug on the diaphragm rim is located in the small cut out on the body 

or................ to save any faffing about turn the carb to manifold gasket upside down and you block the air bleed for good

it is purely to aid emission  results when over heated  but if incorrectly set will affect the whole running of the engine as the mixture will never be correct 

Just Do It

Pete

[Adrian]

I did wonder at the time, so will probably reverse the gaskets.

[Pete Lewis]

yes thats easy, do check your needle position

Pete

[RichardS]

On 04/06/2020 at 09:51, Adrian said:

When I've started the GT6 its struggled to achieve a nice even running and chugs, almost dying until it is up to temperature. Since upgrading to a club electronic dizzy it starts really well and I've been wondering if it is either the choke or compensators (I maybe stupidly, reversed the gasket to unblank the compensator). Whilst I want to get it sorted I also found the following article on the vintage triumph register which you may know about and have dismissed as poppycock!

Your thoughts would be appreciated.

THE ART OF TEMPERATURE COMPENSATOR ADJUSTMENT

by Steve Sutton, ssutton@ridgecrest.ca.us

 

Today I decided to remove the temp compensators from my GT6 and test/adjust them as described in Adrian's post above as I thought that would be a good introduction to Stromberg tuning before I start on the fiddly stuff. I removed the compensators, cleaned them up a bit and found the everything seemed to be OK from a visual inspection so I then decided to make sure that the air passages through the carbs were clear with an air line, which they were, and then finally turned to the air filter housing to make sure that was all clean and free-flowing.

The picture below is what I found. The red gasket looks like the original but the second black gasket clearly has the compensator air passage blocked off so presumably this gasket is from a pre-compensator car? Anyway, I've put the compensators back on and I'll leave them out-of -service for now as I don't want to end up with a lean mixture at higher temperatures as it might already be running a little on the lean side.

As a cautionary tale, yesterday we replaced the water temperature gauge which only has L and H with a new gauge and sender which shows the actual temperature. It's a modern gauge and has an LED for night illumination but to simplify the wiring we decided to have the LED on all the time which meant that we just needed one 12V switched feed. We couldn't wire it in parallel with the fuel gauge as we needed 12V for the new gauge so we took the 12V feed from the nearby live side of the rear window demister.

When we switched it all on, the gauge read zero and the LED flashed on and off about two or three times a second. After a few minutes with a multimeter, once we had replaced the temperature compensators, we deduced that the rear screen demister was somehow connected through the bimetallic voltage stabiliser .... as, therefore was the windscreen wiper motor and, unbelievably, the ignition system. The ignition system had therefore been receiving a pulsed 10V rather than a steady 12V. 😞 

We switched over the two spade connections behind the dash which the last owner had put on the wrong way round and, suddenly, the wipers work properly, the rear screen demister red light shines brightly rather than a dull glow and the engine runs smoothly at idle .... which is exactly what were were hoping to solve with the carb re-tune.

It's a voyage of discovery far beyond our wildest dreams. 🙂

Richard

[Adrian]

Hi Richard

i think you are on the wrong side of the carbs as I believe the temperature change is via the inlet manifold hence the cutout on the manifold side.  

Although im not sure what the additional cutouts are for.

cheers

Adrian

[RichardS]

1 minute ago, Adrian said:

Hi Richard

i think you are on the wrong side of the carbs as I believe the temperature change is via the inlet manifold hence the cutout on the manifold side.  

Although im not sure what the additional cutouts are for.

cheers

Adrian

That's interesting Adrian .... I haven't removed the carbs from the manifold yet so I may be barking up the wrong tree .... however, when I put an air line into the hole in the front of the carb, (the one which is blocked off by the black gasket), the air rushes out of the aperture in the side of the carb where the "spigot" and valve of the compensator fit into.

I wonder if the aperture in your photo is where the air goes into the manifold after the compensator has opened instead of it going through the main choke bore?

Richard

[Adrian]

Will have to wait until older and wiser heads comment, I’m a first timer for everything triumph as well!

[Pete Lewis]

older maybe wiser  ????  you are sort of correct the air feed prior compensator does enter from te front face vent , the raface should only be open if the TC s open and bleeding air to bypass the throttle  plates 

fitting a gasket over the front or rear port will gag the thing

but make sure you gag the right hole .

and in the simplest terms  block off or  just screw the bi metal strip nut to get it CLOSED  for good 

ignore the myths  and waffle get the base mixture set and drive 

it s only there for hot emmission improvements the only effect on any  normal running is due to being open when it should be closed and your  mixture is adjusted to compensate the error.

Pete

[RichardS]

13 hours ago, Pete Lewis said:

older maybe wiser  ????  you are sort of correct the air feed prior compensator does enter from te front face vent , the raface should only be open if the TC s open and bleeding air to bypass the throttle  plates 

fitting a gasket over the front or rear port will gag the thing

but make sure you gag the right hole .

and in the simplest terms  block off or  just screw the bi metal strip nut to get it CLOSED  for good 

ignore the myths  and waffle get the base mixture set and drive 

it s only there for hot emmission improvements the only effect on any  normal running is due to being open when it should be closed and your  mixture is adjusted to compensate the error.

Pete

Thanks Pete

I looked at the air filter mounting flange on this diagram: http://zenithcarb.co.uk/carbspec/carburettor/spares/id/4034/ of my 3432 150CDSE carbs which shows the intake vent for the temperature compensator just below the right hand filter mounting bolt. This is the vent which is blanked off by my black gaskets.

However, both my carbs, and both the red and black gaskets, have another vent hole just above the each of the bolt holes. For some reason, these two vents are not included on the Zenith diagram.

I've now reinstalled the air filter so can I ask if you happen to know what these other two vents are for?

Richard

[Pete Lewis]

they are vents for the float chamber ,  block them and chaos reins 

one is direct float vent one is used on later emission controls and on a base CDS CDSE is vacant   

https://app.box.com/s/qnc1py2hx8hkro9f8o8a

Pete

 

[NonMember]

1 hour ago, RichardS said:

However, both my carbs, and both the red and black gaskets, have another vent hole just above the each of the bolt holes. For some reason, these two vents are not included on the Zenith diagram.

I've now reinstalled the air filter so can I ask if you happen to know what these other two vents are for?

There are two obvious vents required on Strombergs, excluding the temperature compensator. One is the ambient pressure feed to the bottom of the diaphragm - I think that's the elongated one directly above the main airway. The other is the ambient pressure feed to the float chamber (often described as a "breather" or an "overflow" but its real purpose is to put atmospheric pressure above the fuel). I think the two small holes you identified are those.

[RichardS]

3 hours ago, NonMember said:

There are two obvious vents required on Strombergs, excluding the temperature compensator. One is the ambient pressure feed to the bottom of the diaphragm - I think that's the elongated one directly above the main airway. The other is the ambient pressure feed to the float chamber (often described as a "breather" or an "overflow" but its real purpose is to put atmospheric pressure above the fuel). I think the two small holes you identified are those.

 

3 hours ago, Pete Lewis said:

they are vents for the float chamber ,  block them and chaos reins 

one is direct float vent one is used on later emission controls and on a base CDS CDSE is vacant   

https://app.box.com/s/qnc1py2hx8hkro9f8o8a

Pete

 

Thanks for the info and the link. I wonder why the diagram of my exact carb on the Zenith site is not right. I would have thought that they ought to know better than anyone?

Anyway, it's all good. 🙂

Richard

[Pete Lewis]

i keep saying the one little bit of critical clue is always missing , its not just triumph who were good at this 

carburetors and overdrives have the same headache   

without a search stromberg dual  arm floats can fit upside down   find that in the manual  ???   

Pete

[ludwig113]

On 04/06/2020 at 12:35, Pete Lewis said:

old and  wonky are best closed to a permanent shut ,

they do or should only open up with high under bonnet temperatures and this increases the idle and weakens the mixture by allowing a small air bleed to bypass the throttle plates 

they are when old normally found to have the small plastic plunger partly open at cold and normal temereatures ,, this you do not want , you cannot set the idle mixture if the air bleed is open 

so remove the small housing and its plastic cover  you can tickle the the plunger to see if its open , note there are two 0 rings to seal the housing to the carb body these need to work or air is sucked in regardless of any setting . to close it  screw the small nut to pressure the plunger down its bore .

the mixture should be no dark art, on CDSE the needle is adjusted by sticking a hex key down the dashpot tube,  the needle has a small delrin washer attached to its upper end this must be flush with the base of the air piston 

if the diaphragm is all baggy  wash with petrol will return it to size , make sure the small locating lug on the diaphragm rim is located in the small cut out on the body 

or................ to save any faffing about turn the carb to manifold gasket upside down and you block the air bleed for good

it is purely to aid emission  results when over heated  but if incorrectly set will affect the whole running of the engine as the mixture will never be correct 

Just Do It

Pete

i remember you going thru this on one of the "twiddle" days, good info.

cheers

[Pete Lewis]

i wonder if there will ever be any more twiddle days 

I had a heart attack   (fixed)  Ray got cancer (on the mend) and then they invented a blasted virus that Norton cant cure 

Pah humbug 

 

Pete

[ludwig113]

19 hours ago, Pete Lewis said:

i wonder if there will ever be any more twiddle days 

I had a heart attack   (fixed)  Ray got cancer (on the mend) and then they invented a blasted virus that Norton cant cure 

Pah humbug 

 

Pete

there will be more , i've worked thru the whole of covid so i have a slightly different view of it, but we will get back to normality