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Triumph TR6 - Carb Assistance re: Vent Lever Assembly

On the Stromberg Carbs the Vent Lever (adjusted by the Slow Idle Screw), makes contact with a Spring Loaded Pin when the accelerator is not depressed, see http://www.streamload.com/johnston21 for a picture.

This pin (on the carb closest to the firewall) is not always going in the full amount when the Vent Lever makes contact (when the accelerator is not depressed), causing an idle of approx 3000 rpms. If I "flick" the peddle (or the control rod assembly) the pin will usually go in completely, allowing the idle to be at a normal rpm.

Externally inspecting this pin, it appears to be catching something from inside the carb assembly, almost as if it is bent a little.

I've reviewed the White and Haynes manuals as well as the blue Roadster Factory catalogue, but I cannot find where this pin is listed.

Would someone please confirm this pin's actual name, and if you can, advise if this is a DIY repair or not.

Many Thanks,
Peter...
P Johnston

This may be off base, but how are your throttle shafts? I had the same issue with my carbs until I installed new shafts and bushings.

hope this helps
Tim
Tim Brand

Replaced the bushings in early-April, all ok there.
P Johnston

Try taking the throttle pressure away from the levers and they should travel back and forth with no problem. They are there as part of the emissions system and will not cause your idle to go that high if open.

I suspect your linkage is at fault and not the vent lever, make sure you adjust and balance your carbs when they are disc from each other. Once you set your idle to approx 800rpm you should find the lever will be fully seated against the housing.
Cheers
Charlie
Charlie B.

When the throttle pressure is applied, the one spring-pin in question does move fully outwards, but it does not always go in the complete amount when the lever makes contact (when throttle pressure is released). Pushing it in by fingers has shown it to be sometimes catching something internal to the carb assembly.

If the car is running when this happens, it idles high, but returns to normal if the spring-pin is given assistance to be pushed all the way back in.
P Johnston

Peter

I had the same problem. And yes it certainly seemed to be in the carbs. The rear one on mine. It wasn't the linkage because when you would slowly ease it off while watching under the hood you could see that the carb was sticking slightly open. I had replaced the throttle shafts as well. I was too busy (lazy) to take the carb apart so I rigged up an extra return spring to give that little extra closing power it needed. This worked well. You have to be careful when you use the choke though, press the accelerator first and then pull the choke. After a 1000nd miles or so I removed the spring and everything was back to normal. Not the technical approach; but it worked!

Doug
Doug Campbell

Is it possible the slot screw and nut on top is catching it ? I just took off the lever ( it's held in place with a u-clip ) and the the spring loaded pin travels freely but I don't see how to service it. I think when yours sticks its just pushing on the throttle..try taping it in the closed position and see how it runs.
Charlie B.

I bet you have some dirt in the vent piston passage. Remove the hose from the vent nipple on the left side of the carb and attach a length of tubing to the nipple. With the engine off, blow through the tubing and operate the throttle off-idle. Off-idle, you should feel a restriction; at idle, you should be able to blow through. Doing this several times may dislodge any dirt. This valve does not appear to be servicable based on the 1973 service bulletin I'm looking at.

Rick O.

[When the throttles are opened, the vent valves close off the vent passages and the float-chamber
outlets are vented internally through the drillings to the carburetters side of the air cleaner and
any fumes consumed by the engine.]
Rick Orthen

Rick, I agree. The portion of the piston that sticks out was somewhat dirty. I've used an abondance of appropriate spray on it to clean it up and work it back and forth by hand.

This is when I can feel it catching sometimes when I'm pushing it in. As if it's catching on the vent piston passage's side. Could almost put it down to feeling like a bent pin.

You mention this doesn't appear to be a servicable part.

All, is anyone able to locate this part in any of the manuals?

Thanks again,
Peter...

P Johnston

I had the same problem as well and could find very little info about this part. Its not on all SU carbs. I think its a pollution control vent and I by passed it (took it off) and it seems to run fine.

Does this sound right?

Bryn
Bryn

Rick, I think I found the 1973 service bulletin you referred to at http://www.mv.com/ipusers/last/emissions/emissions.html

Also found a little info and good pics at http://web.archive.org/web/20020911155505/www.buckeyetriumphs.org/technical/Carbs/CarbsI/CarbsI.htm

Anyway, more cleaning and (teflon) spray lube has been needed. Also sprayed in the Vent Port accessible when the air cleaner is removed, and "blew" as you suggested.

Removed the Vent Lever for cleaning and found that by replacing the inner nylon sleeve flang the opposite way it allowed the lever to be about 1mm different, or closer to the carb assembly.

Seems to be ok (for now).

Thanks all...
P Johnston

That's great Peter! Now on to the next bit of drama with our cars . . .

Rick O.
Rick Orthen

This thread was discussed between 22/05/2005 and 27/05/2005

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