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Adjusting idle speed

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M

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This should be a simple procedure, but I have gotten a wide range of instructions from local friends. The question is: how does one adjust the idle speed?

First let me say that the carbs have just been rebuilt and balanced. So all that should be working properly. At idle, the tach shows about 1300 rpm. Any lower and the idle warning light comes on far too often and the car stalls or threatens to stall at the idle. But at 1300, to me the engine seems to be racing.

Some people listen to the car and say that the idle is "too high." Some listen to the car and say the idle is "just right." I don't have clue.

Is there a simple procedure for adjusting the idle adjusting screws if everything else is working OK?

This is a really basic question, but I'm currently at that level. Eventually, I hope to move up. (However, I have learned that there are no simple solutions to TR3 issues... Things are ALWAYS more complicated than expected, despite the fact that the car is a simple car powered by a tractor engine.)
 
Have you checked the accuracy of the tach?

If it really won't idle at 1000 rpm, there must be some reason why. Could it have a radical cam? Otherwise it's the usual drill of ignition, mixture, valve lash, etc.

My 56 idles at 800 rpm (+/- 100) indicated, and the red light stays off. Only time it dies is when yours truly doesn't give it enough throttle when letting out the clutch (the aluminum flywheel makes it easier to kill).
 
A mechanic friend of mine has questioned the accuracy of the tach and says he will check it the next time I am in his shop.
 
My car idles at 1000 rpm, but the red light glows. If the car idles at 1300 rpm, the red light glows dimly. (To add to the confusion, my lights are switched, so the ignition warning light glows yellow.)

I am use to newer cars where if the engine light comes on, there is a problem. I realize that the ignition warning light on the TR3 is supposed to come on when the car idles, but it is very, very disconcerting to me and I'm not sure how to react to it. Warning bells go off in my mind. If you can reassure me that the light should glow when idling, I would be much relieved.
 
These lights are not at all like the ubiquitous "Check Engine Light" that you see on modern cars.
Assuming you are referring to the red IGN light glowing when at idle, this generally is a sign of a charging problem to the battery, ie there's more juice coming out of the battery than you are putting into it with the generator or alternator.
Assuming you are still using the original generator the charging at idle is always marginal and the light "might" glow dimly at 800 or 900 rpm (more so if you've got headlights on) but should not glow at 1300 rpm.
Alternators do a lot better at idle speeds and definitely shouldn't cause the lamp to glow at idle.
I would guess you need to take a look at the charging system, particularly the generator.

Now if it's the yellow OIL light that's coming on at idle you've got poor oil pressure (or a malfunctioning oil switch), this is usually a result of worn main and rod bearings.
 
Uhm, except of course that a stock TR3 has no oil light ... the yellow (or green on later 3A/B) light is for the turn signals.

And the red light on a TR3 should not come on (after being off) until current actually begins to flow backwards into the generator (regardless of whatever other load is on). If it does, it may indicate that the cutout is not adjusted properly.

TR6 is a different beastie of course; for one thing, it doesn't even have a cutout ...
 
Well... about four days ago, I had to have my regulator and my generator replaced (they were both only a month old) because somehow they had fried eachother -- some kind of malfunction. So the regulator and the generator presently in the car are both brand new.

It is the red ignition light that comes on when my car is idling at 1000 rpm or even 1300 rpm. The battery, although not new, is in good condition. So I don't know why I am getting this signal at that idle speed.

Before my regulator and the generator were replaced, the red ignition light only came on when I started the car and then did not come on again while the car was running. Now, with the "new" new regulator and generator, it comes on whenever the car drops to idle speed. (Adding to the mystery is that the Triumph manual says that the light should come on when idling.)

The only good sign is that the red light goes out whenever I accelerate. And the ammeter shows charging taking place.

Getting back to my original question: can someone let me know the procedure for adjusting for proper idle speed?
 
Set the ignition timing first.
Adjust the carb's fuel/ air mix.
Loosen the linkage between the 2 carbs so that they are idependant
Balance the carbs with the throttle stop screws to desired idle speed. Reconnect the linkage between the carbs.
That's the basic procedure, but notice it all begins with proper ignition timing, point gap.
Really,valve lash if starting from scratch.
 
Many thanks. The carbs have been balanced by a professional mechanic, so I don't think I need to do that. I have seen mechanics simply adjust the throttle stop screws up or down a little without doing anything else to the carbs or loosening the linkage between the 2 carbs. They balance them "by ear."

What I don't know is how mechanics do this. Do they adjust the idle screws to the point where the engine almost stalls, and then turn the throttle stop screws a certain number of turns to where the idle is right. With one carb, that would be easy, but how do you do it with two carbs? Or am I missing something?

I would like to avoid going to a mechanic each time the idle is a little high or low.
 
Lex:

Two aids for you. This from John Twist on an MGB with HIF series, but the overall method is the same:

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And here's a good written step-by-step article (Lots of them out there on the 'net; this one is typical):

https://www.gerull.nl/mg/technics/carb/carb_tuning.html

Let us know how you do!

Mickey
 
Well.. if you trust that they really are perfectly balanced, then turn each throttle stop screw an equal amount until you have reached the correct idle speed.
If you think it's too low, turn each screw clockwise the same amount; too high, then counterclockwise..
 
If you're not already in a local car club (be it Triumph or all-marque) you might benefit from joining one.

Our club (about 2500 miles to far west for you) has regular tech days plus informal interventions to help members master the basics that every owner should be familiar with (points, timing, carb sync, mixture adjustment & valve adjustment).

The response when shown the technique is similar to being shown how a magic trick is done -- 'Is that all? I thought it was going to be something tricky'.
 
Hi, Mickey,

That's exactly what I needed to see. Many, many thanks.

Since I have just had the carbs rebuilt and adjusted by an expert, I don't think I have to balance the carbs at this time. I believe that all I need at this point is to follow step 6 of the Midgetplace instructions: adjusting the idle. The instructions say: "The easiest way is to screw one of the screws out till it doesn't even touch the throttle stop, then use the other to get the idle speed right. When that's done, you can screw the other stop screw down till it just touches the stop on that carb and you're set."

Again, I believe I can limit myself to doing this because all the other work on the carbs has been done. (My idle seems a bit high -- 1300 rpm -- so I want to see if the car operates OK at, say, 1000 rpm).

One more question, though, and it is the question that has led me into this search. At 1000 rpm, the ignition warning light comes on and stays on until I rev up the engine and accelerate. Is that normal?
 
Thanks George. I do belong to a British car club, but I don't think they have any tech sessions. What a great idea! I'll ask about it.

It's pretty hot and humid here in old Virginia. What a great day to be up on Mt. Lemmon. I wish I were back there in the "dry" heat.
 
Curious as to why this expert who rebuilt and adjusted your carbs left you with such a high idle ? Any idea about that ?
 
Again these tachs and old ones in general may or may not give you an accurate number, I encourage you to see exactly what the RPM is at idle. Does it seem high or are you just going from the tach reading?
 
LexTR3 said:
Hi, Mickey,

That's exactly what I needed to see. Many, many thanks.

One more question, though, and it is the question that has led me into this search. At 1000 rpm, the ignition warning light comes on and stays on until I rev up the engine and accelerate. Is that normal?
Click to expand...

From my experience, no, that's not as it should be, if the generator, regulator, and battery are up to snuff. Eric's suggestion about the tach being off is a good one. If you have access to an electronic tach that senses spark from the coil wire, it may be helpful to compare.

If it is indeed 1000 rpm, then you still have an electrical issue to sort out, I would think. While I don't know when the light "should" come on, I would think it would be more in the 500 range.

Anyone else want to weigh in here?
 
Oh, and don't forget the number one rule: CHECK YOUR GROUND CONNECTIONS! Especially the strap from the engine to the frame. Usual suspect for most electrical issues.
 
Getting back to the idle question.......

Check that the ball joints on both throttle arms are free and oiled. Otherwise they build up friction and hinder the return to idle.

Check that the return spring is still on the accelerator lever at the firewall -engine side.

Check that the pivot pin is lubed on the bellcrank under the front carby.

Check the tension on the throttle return springs on the spindles. Adding tension obviously helps return the carbies to idle.

Many TR's I've seen and including my own, have an extra throttle return spring. It's usually installed from the bellcrank to the generator slotted adjustment arm.

If there's still trouble then double check that the butterflies haven't got out of sync when the W clips were tightened. It happens. Set the idle of each carby seperately again (with a W clip loosened). Press down hard on both idle screws when tightening the W clips.

Regards,

Viv.
 
I second Viv's caution about double checking when tightening the W clips.
I very carefully adjusted the carbs recently, went for a drive and had a warmed-up idle that was way too low. Turned out to be one throttle disc out of adjustment. I have no idea how it happened, but something slipped or was binding a little before I tightened everything up.
John
 
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