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TR6 Triumph TR6 Carburetors

cannon

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My TR6 ran well. I parked it in the garage. 2 weeks later it would not start. After alot of monkeying around I measured the fuel level in the jets, both were 1 plus inches, much too low for fuel delivery. More monkeying, I found the fuel pump pressure less than 1/2 psi. Rebuilt the pump, now it's 2 1/4 psi(right in spec.) The fuel level in jets went to approx. 1/2" now, still too low. I measured the float levels, they were 17mm, I reset the floats to 16mm. The fuel level in the jets is now about 3/8". It runs OK now but both needles are set to full enrichment. I can not understand what happened, why the fuel level dropped just sitting in the garage for 2 weeks.
BTW: the math. conversion mm to inches in the Triumph shop manual and Haynes manual is incorrect. The authors flunked 3rd grade arithmetic.
 

poolboy

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I use the inch measurement. .625 to .627.
As to why the level changed.....?
Funny that it ran good with a poor fuel pump, too.
 
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cannon

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I measured the fuel height in the jets with a coffee stirrer as a pipette. The coffee stirrer is perfect to slide down the jet hole to bottom. I slid a piece of rubber tubing on the stirrer to mark the face of the jet. The stirrer is almost transparant so I can see the difference between the fluid level and the jet face. My friend assures me this should be < 1/4" but I don't know.
 
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cannon

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I suspect the fuel pump diaphragm was failing for at least a year because it was getting increasingly more difficult to start. I think it just finally got to the failure point. I'm thinking that ethanol in gasoline possibly caused the rubber compound diaphragm to loose it's elasticity. The new diaphragm was somewhat more supple but not alot.
You set your floats to 16mm (.625") which is where I finally set mine. I used the mm spec. because of the confusion over the math conversion and the mm specs are consistant in the references.
 

poolboy

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I can't say that I've ever heard of measuring the fuel level in the jet. Naturally, it will be at the same level as the float chamber when the engine is not running.
An interesting experiment, nonetheless.
 
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cannon

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The floats control the fuel level in the jets but the floats are adjusted in the upside down position so you can't know how high the fuel rises in the jet unless you measure it this way.
I am completely baffled by this situation and was hoping someone out there confronted it before me. So far no luck.
My background is Mechanical Engineering but 53 years ago in my past life I was an auto mechanic in the US Air Force. I attended several tech schools for auto mechanics. These old engines are duck soup to a very old mechanic that's now retired.(did I say very very old?)
 

poolboy

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I understand that, cannon. But you set the float level according to the specs. There's no way to have one level in the carb's float chamber and another level in the jet when the engine is not running. So you set the float level and the level in the jet will take care of itself, until you start the engine and let Venturi take over.
Is this just an academic question that's haunting you or is there a pragmatic reason for wanting to know the level of fuel in the jet when the engine is not running ? Maybe I'm just dense but if it were an issue, I asure you there'd be an article on the topic either online or in a Manual.
I guess you could take some measurements of float height, float boyancy, length of jet Venturi tube, barometric pressure and calculate the height of fuel in the jet at rest, but what would that really accomplish ?
 
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cannon

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Setting the floats according to specs, that's the point. Engine running or not the fuel level remains the same according to the float positioning. The float level or more precisely the fuel level in the jet is determined by the designer so the suction on the annular area is appropriate to provide raw gasoline to the engine. This is not just an academic issue it's also a practical determination of the operation of this specie of carburettor. You sound like an educated gentleman, my issue is "what happened to my car", I can't understand it. And you're not dense, you just haven't been here before. Regarding whether there would be an article on the topic on line or in the manual, my guess is nobody ever thought about it except the designer and he guarded this design information, probably took it to the grave by now. But it's out now. What would you do if your car wouldn't start and you had spark and gas? Would you think to investigate the fuel level in the carb jet? Probably not, so what would you do? Anyhow it happened to me and it can happen to you, so now you know. The fuel in the jet must be at some level (must be) so the available suction created by the venturi effect at the bridge of the carburettor can draw enough fuel for the engine. I'm quite sure that level is less than 1/4" below the jet face, I found that dimension emperically not in a manual so I'm not positive. However I can assure you the engine will not run unless it is in that range. Check yours sometime.
BTW: My first name is Joe.
 

poolboy

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OK, Joe it is. I'm sorry I still don't get it. The bottom part of the float chamber is 1.5 inches deep (to the bottom of the plug) The venturi tube extends about 1.3 inches into the bottom of the float chamber. The choke tube about .3 less. If your choke works then you have at least .3 of an inch in the jet's venturi.
If your float level is set at .625 inch, depending on how deep the float sets in the gas you should have approx .70 inches of gas in the venturi when the engine is not running and the needle valve closed.
Are you saying that there is a point where there is gas in the venturi tube but it is too low to be drawn up the tube ?
Hard to believe, when I've run my carbs dry, except for a bit in the bottom of the plug, quite a few times.
And no, I don't think anyone went to their grave with the secret. There's just too many ZS carbs around and too many smart people fooling with them and making their living working on them for the secret to be kept.
I tell you. Joe, set the float level and let physics do it's work. There's going to be enough gas in the venturi tube to run the engine.
There must be some other reason your car won't run.
There's been a lot of people experiencing faulty ignition components here of late, rotors, condensors, even distributor caps.
What is it they say ? " 90% of carb problems are ignition problems" or something to that effect.
Hang in there; this Forum and www.6-pack.org are here to help.
 

tom628

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Joe, I don't know if this addresses what you're getting at, but you could remove the plug in the bottom of the float bowl and replace it with a one-hole rubber stopper with a length of tubing . Run the tubing up along the side of the float bowl and read the fuel level, similar to a water gauge or manometer. I've done this occasionally with motorcycle carbs.

Tom
 
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cannon

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Yes I suppose you could do it that way also. But using a pipette works without all the monkeying around and gives an accurate, easy to read measurment.
 
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cannon

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The engine runs well now, starts easily and goes like a bat out-o-heck. I also advanced the timing 2 degrees to 4 degrees BTDC. I put a new sport coil on it to boost the spark voltage. It has great spark, I checked that first.
What I'm wanting to know is what happened, and I know it's carb related.
Here's a thought(as of last night in bed) What would happen if water got into the float bowl via bad gasoline? Since it's heavier than gasoline it would sink to the bottom of the bowl and close off the route that gas would normally use to get to the jet. Could it be the cause of very low fuel in the jet?
And another thought, I had tightened the brass widget on the bottom of the float bowl to the max. Could or would the widget go so far into the bottom of the float bowl to close the chanel off somewhat and interfere with gas flow to the jet? It doesn't seem likely but I'm grasping at straws now. I can back it out a couple of turns to see what it does to the fuel level in the jet. That's easy, the former will take some doing to test.
When I first encountered this problem the engine simply would not start. I almost burned out my starter motor trying. I have said over the years, if an engine has spark and gas, I can make it start. This issue has made me humble.
The engine started after I finally had the fuel level in the jet to the level it is now, 3/8" below the jet face, but the needles are full enriched. It faltered and stumbled like a lean mixture until I enriched them.
 
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cannon

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Mr Poolboy, are you a member of six-pack. A year or so ago they ran an article in their newsletter about the emergency hood release I developed. I had emails from all over the country after that.
Nice TR6, what year? Mine is a '71
Joe
 

poolboy

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Yeah, Joe; I'm currently a member of 6-pack. Do you have the same "handle" over there ?
About the water, seems like if it were in the venturi tube, it would get sucked up until it got down below the level that the tube could reach in the float chamber. With the carbs that have the brass plug, that would be about 1/10 of an inch, between the bottom of the tube and the bottom of the plug.
If you are still running lean, you might want to do what the guys without an adjustable needle have to do and that's increase the level of fuel in the float chamber.
Regardless, I'm glad you're enjoying your car again. And I'm glad I can put this isuue behind me, too. You had my brain in overdrive.
 
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Tinster

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If it's a load of bad gas you've got........
WOW! do I ever feel badly for you.

My car was out of service almost 6 months as result
of bad gas. I had to replace the entire fuel delivery
system including a new gas tank. Had the carbs on and off several times.
Numerous fuel pumps and even the ignition system had to be replaced.
Changed out the fuel lines twice.

Drain your tank and hope and pray this does not flow out. best wishes,

tinster

badgas.jpg
 

poolboy

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Strawberry Daiquiri ? You'd think that 151 proof Rum would burn pretty good.
 
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cannon

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Brain in overdrive is good for you, if you're over 60, so they say.
I'm not in 6-pack. The editor there saw the item I put in our newsletter The Standard (Capital Triumph Register , Washington, Virginia & Maryland) and contacted me for permission to publish it.
I started to raise the levels by reducing the float heights. But then I thought this is nuts so I set them to 16mm per the book. It ran poorly as I described so I kept enriching the mixture, now it runs OK but the needles are full rich.
I don't want it that way so I'll keep plugging till I find the answer.
Don't leave me, you keep my brain in overdrive too.
Joe
 

poolboy

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I'm here a lot lately, Joe. There's a bunch of us here that visit both places and fairly often, too.
You know that you don't have to be a 6-pack member to use the Forum. Over there these days, priority has been given to the # of hits (if you know what that means) that the site gets.
So far, I don't remember seeing anyone who had their carbs more screwed up than mine were when I brought my car home. As you said about the simplicity of the TR6 engine.....the ZS carbs make up for it.
 

TRTUSH

Freshman Member
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Hi There PB,

I may need your help in the future as you are the carb guru in my mind. I just bought a TR3A to go along with the 6. Now I have to figure out SU's.

Cheers,
Tush
 
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