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Carb sometimes sticks at a high idle

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Norton47

Jedi Warrior
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Hello All
Once again I request some insider knowledge.
My TR6 has started to sometimes stay at a high idle when the foot feed is released. Usually tapping the foot feed will get it to drop back down.
What I think I have found. On the rear carb, there is an L shaped arm, this has the throttle stop screw on it, there appears to be two of them, one with a spring that rests against the actuation linkage and one with a nut around it that actuates against this L shaped arm. This arm also actuates a small shaft that goes into the carb body. This small shaft can hang up when returning from a accelerated state to an idle state. Jiggling it allows it to fully return and lowers the idle.
The front carb does not stick in this fashion.
Please see photo, the red pointer is pointing to the L shaped arm and behind the choke cable is the portion of the carb body where the small shaft moves in and out.
https://www.flickr.com/photos/norton47/896411756
What is this small shaft and how might I resolve this issue?
Thanks
 
Just a thought - isn't that L-shape arm the fast idle cam actuator? And shouldn't there be an adjusting screw in it?

(Unless there's already one on the front carb.)

Tom
 
I believe that arm is part of the emissions equipment. The rod closes off the bowl vent through the face of the carb, so that bowl fumes at idle are forced to go to the carbon canister (and the anti-runon valve can lower the pressure in the float bowl).

If it's sticking, likely the valve is full of crud and needs to be cleaned.
 
Thanks Randall
Makes sense and these are 175 CD-2 carbs and have an emissions canister.
Where can I get more details on how to get to the valve.
My Haynes Zenith Stromberg CD carburetors book doesn't seem to cover it.
 
That figure is from a series of articles that were originally posted on the Buckeye Triumph web site, but aren't there any more. If you'll PM me your email address, I'll send you some PDF files. Or maybe someone else knows the link to the web archive for them.
 
Thanks again for the information.
I took the air cleaner off and use some carb cleaner and swabs and cleaned out the passage for the valve. This has rectified the problem.
Thanks
 
As it appears that the TR6 problem is cleared, I would like to hijack this thread for the same problem on an early TR4 with Stromberg's, but without any emissions gear on it.

I normally have a smooth idle at about 750 RPM, but once the engine warms up it only slows to about 1100 RPM after driving unless I give it a quick tiny blip and pull back on the gas pedal with my foot. Just pulling back on the pedal without the blip doesn't work. Any ideas would be appreciated.
 
TRDejaVu said:
I normally have a smooth idle at about 750 RPM, but once the engine warms up it only slows to about 1100 RPM after driving unless I give it a quick tiny blip and pull back on the gas pedal with my foot. Just pulling back on the pedal without the blip doesn't work. Any ideas would be appreciated.
Click to expand...

Sounds like something is sticking mechanically, Do you only see this after you remove the choke? Might be happening when it is cold, but the the choke is covering it up??? I would start by looking for anything which may be binding, or perhaps a missing / loose / weak return spring. Also with dual carbs there is the linkage between them which either could be binding because it is slightly out of line, or maybe just "gunk" which has build up on it.
Either way, start out by cleaning everything with carb cleaner, and then work either from the pedal to the carb or the other way, and look for any bit which is sticking, or doesn't move easily.
 
FWIW, I had similar symptoms with my SUs, when the throttle shafts were so badly worn that the throttle plates were dragging on the bores. Pulling up wouldn't make it idle down, but blipping the throttle would.

ISTR the TR4 linkage is supposed to be adjusted so there is some freeplay at the carbs at idle. You might check that, too.
 
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