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Temperature compensators

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NHinNC Avatar
NHinNC Larry C
Greensboro, NC, USA   USA
New engine rebuild, and carbs rebuilt. I had an issue with a rough engine after thoroughly warming up. One possibility was that the temperature compensators were not working properly. I removed them, and inserted into hot water to see how they worked. I noticed that when warm, the piston/valve had lots of movement on the bimetalic spring. This seems pretty silly top make something to compensate for temperature change, but yet have so much variability in it when activated.
I was thinking of adding a small dab of silicone sealant/RTV to that slot in the valve to keep the spring in one place. Anybody else see this?



1976 TR6 Mimosa Yellow - not original
Purchased July 2015

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LFMTR4 Avatar
LFMTR4 Lou Mijares
Scottsboro, AL, USA   USA
Mine are disabled, it takes all the variability out. I think “The Z-Carb Guru” will tell you that their primary function (as well as the TBV) was to help pass U.S. smog requirements in the more stringent states.

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Fogspawn, CA, USA   USA
1974 Triumph TR6 "Machine"
from peanut gallery, if carbs are "rebuilt" then temp comps are good. they have a seal against carb body, a very thin round seal...
and a seal in the carb body around the nose of the temp comp... easy to miss on rebuild (I did)...
they have a purpose ... and cannot be eliminated without eliminating other components...down or upstream... however you wish to look.
my experience, bought new temp comps (hated the $$) and rebuilds for the bypass valves (and paid real attention
to the instructs and adjusting instructs..., and the seals...(!)

feel that in one of attempted rebuilds I missed on temp bypass bodies, a seal body bypass to carb body, outer, then inner...
when I sorted this out, AND followed procedure for adjusting bypass valve adjustments... the engine runs much steadier...
loves its idle speed behavior...

Unless you intend to execute(eliminate) all the emissions points the carbs, just sealing temp compensators off is not likely to yield dividends...
We eliminate what we don't understand... but makes it run better, faster...? mmm

yeah, the Zenith Strombergs and the weight of the smog police is onerous... but they did beat them back...
and can continue, if you have the will to pursue the solution....I find that most trouble is my own mistakes that I find in retrospect, round 2 or 3...
Humbling but fun... (not if I were a for-profit garage....)
w

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poolboy Avatar
poolboy Ken D
Sandy Hook, MS, USA   USA
Here's one thing you can take to the bank...both of those ancillary components have the potential of affecting the quality and stability of the idle ..and not in a positive manner.



ZS carb repairs
kencorsaw@aol.com

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Fogspawn, CA, USA   USA
1974 Triumph TR6 "Machine"
when they work, they work fine and are benign... yes, they can make much frustration...
yet... eliminating things today and running better... come back to understanding what
the cut-off things do...(I hold my tongue from here)...
w

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F1000RACER Avatar
F1000RACER Platinum Member Gary H
Alpine, CA, USA   USA
In reply to # 1600479 by LFMTR4 Mine are disabled, it takes all the variability out. I think “The Z-Carb Guru” will tell you that their primary function (as well as the TBV) was to help pass U.S. smog requirements in the more stringent states.

True that and it's easy to block both of them off. This has been the norm for decades now. If you don't fully understand their function and have the patience to work with them then block off.

GH

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Darth V8R Avatar
Darth V8R Vance Navarrette
Beaverton, OR, USA   USA
1980 Triumph TR7 Drophead "The Great Pumpkin"
1980 Triumph TR8 "Wedgie"
In reply to # 1600479 by LFMTR4 Mine are disabled, it takes all the variability out. I think “The Z-Carb Guru” will tell you that their primary function (as well as the TBV) was to help pass U.S. smog requirements in the more stringent states.

While it is true that they help emissions, they are there to prevent heat soak and the resulting rough idle from a too rich mixture. If you close them off completely, you are likely to find that the car is difficult to restart and runs poorly for a minute or two, particularly if the car sits for 20-30 minutes before being restarted. The problem can be quite severe when the carbs are running rich to begin with. Needless to say, the emissions are quite excessive when this occurs - so in that sense they are indeed emissions control devices.

To get around this, some people install heat shields. This works, but the engineers did understand the hot restart problem, and the compensators were their solution.

Disabling them may lead you down the path of needing to re-engineer a solution for heat soak. Your choice of course.

Vance



1980 Platinum Metallic TR8, frame off restoration, complete.
1980 Vermilion TR7 Sprint replica, in progress.

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POW Peter Wirth
HEBRON, NH - New Hampshire, USA   USA
In reply to # 1600459 by NHinNC I noticed that when warm, the piston/valve had lots of movement on the bimetalic spring. This seems pretty silly top make something to compensate for temperature change, but yet have so much variability in it when activated.
I was thinking of adding a small dab of silicone sealant/RTV to that slot in the valve to keep the spring in one place. Anybody else see this?

I am a proponent of keeping them and tuning them, You can search a bit and find good info on the adjustment. When our 6's sit in traffic the engine tends to get hot, particularly if you are still utilizing the vacuum retard. As the engine gets hotter the set mixture becomes too rich, idle will drop and get lumpy and emissions will rise unless you have correctly adjusted TC's. Correctly adjusted, they will open as under bonnet temp rises and admit extra air into the Strombergs thus leaning the mix back to where it should be, keeping the idle RPM steady and keeping 1970's emissions in line. In my opinion they are worthwhile regardless of what one thinks of emissions $hit.

However, back to your original query about stabilizing the tapered plastic piece on the bi-metallic blade. Not a good idea. It needs to float a bit to centralize as it seats, kind of like a toilet tank stopper wiggles around a bit before it plops into position. The TC unit is not a highly machined unit so needs this slop to work. Keep in mind it is not metering fuel but air so an even bleed around the tapered plastic piece and it's seat is not important. - Pete

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poolboy Avatar
poolboy Ken D
Sandy Hook, MS, USA   USA
Actually, what happens when the TC valve opens is that the air enters a location in the carb so that it reduces the amount of "suction" on top of the air valve diaphragm that is holding the air valve up....the air valve drops a bit, bringing the needle along with it leaning the mixture.
This is from Triumph's 1973 Emission Control Service Notes:
"Emission testing has shown the need for a temperature compensator to cater for minor mixture
strength variations caused by heat transfer to the carburetter castings. This demonstrates the
extraordinary precision demanded by exhaust emission requirements.
As the temperature of the carburetter rises and the bi-metal strip is actuated, air is bled into the
mixing chamber which causes the air valve to ride in a lower position, in order to maintain
depression on its downstream side. The effect of this is to give a smaller fuel flow and weaken the mixture"

What it doesn't say is that depending upon at what temperature the TC has been set to open, the ambient temperature and how long and how fast the engine has been running the preset TC may have taken upon itself to open or even fluctuate in conditions other than at idle as the temperature changes.
I've found no ill effects or instability of idle by disabling the thing.
People who rebuild carbs, like Joe Curto, Paltech and even myself wouldn't want to return carbs that acted up because of a disabled component.



ZS carb repairs
kencorsaw@aol.com



Edited 2 time(s). Last edit at 2019-03-08 03:41 PM by poolboy.


Attachments:
IDLE TRIM& TEMP COMP.jpg    30.4 KB
IDLE TRIM& TEMP COMP.jpg

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Marksg1 Avatar
Marksg1 Mark Greenbaum
Evanston, IL, USA   USA
1976 Triumph TR6 "Nigel"
Had a rough idle problem 6 mos ago. Ken, AKA Poolboy did a great job of rebuilding them a fews ago so I was pretty sure it wasn't serious. I removed the temperature compensators without removing the carbs. I found one where the adjusting nut had loosened and worked its way all the way out. I followed the adjustment proceedure on the link below, used a touch of locktite, problm solved.

http://www.grampianstags.net/TCs.htm



I love the smell of hydrocarbons in the morning.

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POW Peter Wirth
HEBRON, NH - New Hampshire, USA   USA
Ken, I appreciate the very concise description and fine points of the TC's operation as per the Triumph Emission Control Service Notes. I must confess I never studied closely enough the means to the end of leaning the mix. Very easy to follow along with the cross section drawing. I still stand by what I said about properly adjusted, TC's will keep idle stable when under bonnet temps are high. I don't find adjustment too troublesome so I guess I'll continue to let the little fella do it's thing along with the by-pass valve. - Pete

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NHinNC Avatar
NHinNC Larry C
Greensboro, NC, USA   USA
Thanks for all your inputs, especially to Ken and Mark for your inputs.
Ken, your jpg helped a lot with understanding this circuit.
Mark, the link you posted is what I used to try to adjust them. Looking at the jpg Ken posted, I have a hard time feeling good about the total amount of movement of the piston, considering that there is a large amount of play between the piston and the spring. I may try to get the spring to work a little earlier.
Also, this could very well not be the source of the problem... It could be the coil when it gets hot, or...



1976 TR6 Mimosa Yellow - not original
Purchased July 2015

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POW Peter Wirth
HEBRON, NH - New Hampshire, USA   USA
In reply to # 1601221 by NHinNC
, I have a hard time feeling good about the total amount of movement of the piston, considering that there is a large amount of play between the piston and the spring. I may try to get the spring to work a little earlier.


Whether you keep them or not is not a concern, but if you do, I would not try to tighten up the tapered piece on the bi-metallic spring. It needs that "slop" to slide into place. - Pete

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ed.h Ed Hollingsworth
Omaha, NE, USA   USA
If I recall correctly, the "piston" fits in a bore, which locates and guides it. The bimetal spring just determines how far down the bore it is.

Ed

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Marksg1 Avatar
Marksg1 Mark Greenbaum
Evanston, IL, USA   USA
1976 Triumph TR6 "Nigel"
I found it hard to tell how far it moved. When I put them in boiling water I had to use a flashlight and look very carefully. Ken would know more about it. I'm not sure the actual distance is as important as that the work at the same temp.



I love the smell of hydrocarbons in the morning.

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