Idle speed adjustment

[AltaKnight]

At the weekend I advanced the timing somewhat on my TR6, and it runs a lot better.
As a side effect it also increased the idle speed, I tried adjusting the throttle stop scres out to compensate and get the idle back below 1000 RPM but to no avail, even with the screws right out it still wants to idle at about 1100 RPM..
The throttle linkage up to the throttle shafts is definitely not hanging up so I've come to the conclusion it's a problem in the throttle shafts themselves or else the throttle plates inside hanging up on something. The return springs seem strong enough. The car only has 52000 original miles on it.
Any ideas out there?

 

[Adrio]

I had the exact thing happen. Check for air leaks. Could be anything, a vacuum line, the throttle shafts could be worn, or the holes in the carbs where they pass could be worn, or the butterly in the carbs may not be centred properly.

In my case it was both the vacuum leak (I had damaged a metal line while removing the carb for an other reason) and the butterfly not being centred (I was putting the carb together from memory and I had forgotten the procedure to check this).

In your case the tiiming may have been changed to get the idle down. Regardless, check vacuum lines then check the fit of the butterfly. I used a light to see how much air could pass the butterfly when it is in the idle position.

After doing this my engine went from not being able to idle below 1300 to being able to idle lower then it would hold the idle.

good luck
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[Dave Russell]

Not to overlook the obvious, is the fast idle adjustment completely out of engagement at normal idle?
D

 

[Banjo]

Also check the idle trim adjustment screw on the right side of the carbs.
To check for a vacuume leak, spray a little carb cleaner in the areas of suspicion. If the idle fluxuates you found the leak.

 

[bluemiata90]

I just had the same problem with my TR4A and what I had to do was loosen the throttle plate linkage between the 2 carbs and adjust the idle seperately. I was able to get the idle down considerably, once the idle was down, I tightened the small screws and away I went. It took about 10 minutes. I don't know if this will help or if you've already tried it, but it's worth a try if you haven't.

 

[AltaKnight]

Well, I had another go at this and sure enough there was a vacuum line below the carb that had come adrift, put that back on and it's down about 950 RPM.
I can only get it to 800 by pushing on the throttle shafts directly, feels like Andrio has the right answer, the butterflys must be not centred inside, I assume this can be adjusted with the carbs off?

 

[Adrio]

You are going through the same steps I did. I fixed the vacuum leak and then I had to push on the linkage to get the last little bit. That is when I centered the butterfly and it was fine. Yes this can be done with the carbs off the car. I used a light. I look through the carb with the light on the other side of the butterfly as my eye. You see where the gap is. Then loosen the screws that hod the butterfly and slid and or twist the butterfly in the direction of the gap. Remember the butterfly is not round so a slight change makes a noticealble difference with that oval (or whatever shap it is). Wit a few iterations you will get it just great. Then you will have to raise the idle, beleive it or not.