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TR6 TR6 carb question and running rough

bigbadbluetr6

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Lately I have been having problems with my TR6 running good. Attached is a picture of some sort of vacuum something, each carb has one. These have always been open. Lately they are hissing when the car is at idle and making it run a little rough. When I cover up the holes the idle smooths out a little bit.

My symptoms have been the car will run real rough for a few seconds and then run normal again. I blurp the throttle and then it runs good again. Sometimes the car will die at idle. Revs help out with this problem.

I have replaced the diaphrams, plugs, wires, coil, rotor, fuel filter and run some injector cleaner through a tank of gas. I have been putting in 91 octane. Any ideas why my car will have these periodic spells of running bad? I plan on attending the Brits in the Ozarks show this weekend so I do have a deadline. My next step of action is to replace the fuel pump.

My car is a 73 but it looks like the carbs are off of a 74. The tags say 3613.

Thanks
Eric
 

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poolboy

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That is a nipple thru which the Throttle Bypass Valve (TBV) of the 74 carbs sensed manifold vacuum.
Obviously you do not have it plumbed like a 74 so if you find capping it is having some effect it's probably because the TBV diaphragm is shot, brittle and leaking or floating..Therefore you should turn the TBV adjustment screw as much counterclockwise as it will go.
In this picture you will see the adjustment screw like your's on the TBV on the right. The TBV on the left also has an adjustment screw but it is concealed under the brass tamper proof cap.

One more thing.
The big nipple sticking up at an angle in your picture is an evacuation port designed to relieve excessive crankcase pressure via a hose connected to the valve cover.
Actually both carbs have the evacuation nipple and originally both were connected to the valve cover with a "T" fitting.
Connecting the valve cover to one and capping the other may work for you as it does for me..but at least one needs to be connected to the valve cover.
 
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bigbadbluetr6

bigbadbluetr6

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Can I replace the TBV diaphram?

i have the evacuation hole plugged into the other carb, the valve cover and it goes upto the canister. I noticed a difference in how it idled when taking both of those hoses off. I can't remember if it helped or hurt the idle.
 

TR3driver

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Can I replace the TBV diaphram?
That would be my suggestion. In fact, if those diaphragms are shot, likely the other seals and so on are ready to change as well.

The diaphragms are usually included in the "rebuild" set or I think TRF will sell you just the diaphragm. The Buckeye Triumphs site has some really good articles on how to service these carbs, including what all the ports & adjustments do.
 

poolboy

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I don't believe the TBV diaphrams are included in any of the rebuild kits...but TRF, Moss and VB sell the diaphragms seperately.
When ordering be sure to differentiate between the "assembly" and the "diaphragm"

BUT the reason I suggest disabling the TBV is because you have no method of working it properly.It requires the ability to sense manifold vacuum to function.
Where would you connect the 2 sensor nipples ? The 74 made provision for this at the Thermostatic Vacuum Switch manifold... You have that ?
It's similar to this EXCEPT it has 4 nipples not 3.

I see no advantage to replacing a diaphragm..just stop the leak by compressing the valve against the fuel passages in the method I described..
Disabling the TBV is a fairly common practice..either by the method I described ...OR as I and others have done, by making a solid gasket that covers these passages.
In this illustration there is a "Sensing to Manifold" port..but the 74 uses the external nipples to sense manifold vacuum and make the valve work...
If the TBV were not leaking..I don't think you'd even be aware of it and whether it was disabled or working normally.

 
Last edited:
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bigbadbluetr6

bigbadbluetr6

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I don't have the Thermostatic Vacuum Switch manifold.
Here is a picture of my current set up
Would my petronix be going bad? I've read where people have had problems with it and switched back to points and condenser.

image.jpg
 
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bigbadbluetr6

bigbadbluetr6

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Update. I plugged the 2 snorkel things in the first post on both carbs and drove to Victoria British(10minutes). After that it ran pretty well. It had a little stumble at one point but never happened again. I took it out on the highway for a few minutes and didn't have a problem. Maybe this is a temporary fix. I guess I'm planning on rebuilding my carbs this winter. I also replaced the fuel pump today. Maybe that will be part of the problem.
 

pdplot

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Every time I read one of these posts, I thank the Lord I have an early ('71) TR6 without all that extra crap. I remember with nausea the 1973 cars with seatbelt interlock where you couldn't start your car with an unlocked belt, and the 1974's with a ton of anti-smog crap. Couldn't you guys just swap out for a pair of early Stromberg's or SUs instead of frustrating yourself with all that extraneous garbage? I sure as **** would try.
 

poolboy

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Nothing like a bit of carb snobbery.
AFAIK the only difference, the only real difference between your 71 ZS CARBS per se and the later ZS CARBS post 72 was the addition of the transition valve for the float chamber vent..
 
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bigbadbluetr6

bigbadbluetr6

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Car is still not running right. Here is the problem. One day while driving a few weeks ago it started to sputter acting like it was cutting in and out causing a herky jerky reaction while under power. Take away the power(load) and the engine was missing while revving. After some attempts(probably less then a minute) to put power(load) and revving in neutral the problem went away.

I have noticed this problem has happened on more than one occasion and maybe all of them when I turn left. Seems kind of strange to me.


The car accelerates and decelerates pretty well. Just while cruising around the motor still seems like it is missing a little. The idle is slightly rough.


I've changed plugs, wires, cap and rotor. Changed the diaphragms in the carbs which were bad. Not a surprise. Replaced the coil. Tried to replace the fuel pump but the one I got from Vic British leaked. Adjusted the valves. I have petronix and that is one thing I've considered changing it back to points to see if that helps.


The carbs or distributor might be the problem. Might need to rebuild them.


Thanks for taking your time and reading. I've been going through the progression of things that could be wrong. If there is a simple solution let me know.
 

Gliderman8

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Have you replaced your fuel filter? The only reason I ask is that I don't see it in your "list of things" that you've done. Clogged filter, no fuel... no fuel, no go.
Just a thought.
 

poolboy

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if you replaced the carb air valve diaphrams , there's not much else regarding what you've described that you can blame on the carbs.. EXCEPT an adjustment...then there's those Throttle Bypass Valves that you've dealt with in your own way, but from the description of your current problem, I don't think they are to blame..They will show a fault at idle and engine over run..not during acceleration or cruising steadly along.
Let me see if I can list all the possible things that can be adjusted (or maladjusted) on the TR6 carbs
Mixture ..70-76 years
Float height .. all years
Choke engagement..all years
Idle speed..all years
Idle trim...all years
Temperature Compensator...all years
Synchronization...all years
Throttle Bypass Valve...all years
Float chamber vent valve...73-76
....I think that's all...
Here's the thing, 3 of those adjustments on the 73-76 carbs are interrelated..adjusting one of them may have an effect on the other 2
They are the float chamber vent valve, the idle speed and the choke engagement.
So replacing carb parts with what may or may not come with the rebuild kit is just part of the process and from what I've seen if there was a screw that was accessible, someone has turned it trying to compensate for a problem...similar to what I was trying to get you to do with your TBV's
 

Tosh

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I have noticed this problem has happened on more than one occasion and maybe all of them when I turn left. Seems kind of strange to me.

FWIW Used to happen to me too. I ended up resetting the float level of the inboard carb and removing and cleaning the float needle (Grose Jet).

 

sundown

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I also own a 73 TR6 I corrected the problem by taking of the air filters an inserting a cherry bomb in the mouth of each carb and then lit them it corrected the problem and I purchased 2SU carbs easier to work no idle problems either
 
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