• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

Valve check

Share this page

If you haven't yet, watch John Twist's two other SU videos (43 secrets of the SU carb, or something). Gives a good explanation about how the carb works and what the parts do. I find that helps me a lot, more that just following instructions.
 
Darrell,

When I viewed the John Twist video recommended earlier, I saw that there were others. Thanks for the tip. I intend to look at all of his videos on SU carbs before checking on the pistons in my carbs.

I welcome all the information I can get.

I, like many of you, get pleasure not only driving down the highway but in knowing, to some degree, what is going on in the car and with the car, and in having the confidence to know that if something, although probably limited to minor problems, were to happen, I probably could fix it. That's part of the pleasure.
 
Hey Ed...if you get near your 4,000 miles, just drive backwards for a while to get the odometer back down!

John
 
Hi, John,

Well... I never thought of that. Of course just driving through Ole Virginny has been known to turn time backwards, so I should actually be losing miles rather than gaining them.
 
Next time you're out driving your TR, drive it half a mile backwards and watch the mileage on the speedometer increase as you are moving backwards.
 
Now you're just confusing people with facts!

Besides, if you're driving a half mile backwards, I strongly suggest you watch where you're going instead of the odometer!
 
Getting back to carbs for a moment.... I will check to see if the pistons have been swapped (causing one to fall more slowly than the other). This seems fairly straightforward.

But I may also have to center the jet.

The instructions that came with the SU tuning tools is pretty cryptic. Can someone clarify this for me.

Here are the instructions:

1. "Remove the suction chamber with piston and replace the jet needle with the centering pin." Removing suction chamber and piston...OK, understood. I assume the rest of this sentence means loosen the locking nut on the jet needle, take out the jet needle, and insert the little pin that comes with the kit and tighten.

2. "Lower (or remove) the jet to the lowest position and slacken the jet locking nut." Not sure of the procedure or sequence here. How do you lower the jet, and do you do it before you slacken the jet locking nut? The only illustration shows a hand pushing down one of the tubes that come with the kit into the piston, but the illustration shows the suction chamber and piston back in place. Is this how you lower the jet?

3. "Refit the chamber and piston." Now or earlier?

4. "Slide the centering pin into the jet bearing and tighten locking nut." I assume the centering pin slides into the upper jet bearing as you are refitting the chamber and piston.

5. "If the piston cannot be moved with the centering pin in the jet bearing, slacken the locking nut again and repeat until the centering pin can be moved in and out of the jet bearing." If piston cannot be moved up and down... OK. Why would the centering pin keep the piston from moving? Rubbing on the inside of the jet bearing? Does the locking nut cause the jet to canter to one side or the other? How would repeating this procedure give some other result?

6. "Check if the needle is bent by rotating the piston in the suction chamber." But no mention or replacig the needle. I assume you replace the needle between steps 5 and 6.

If you have better, clearer instructions, and have a few moments to include them here, I would very much appreciate having them.

Practical Hints also has instructions, but they are also confusing, and John Twist's explanation seems to require that you take the carb completely out of the car. Twist shows all the components in great detail, but when it comes to the actual centering of the jet, he works quickly and doesn't explain what he is doing. Just twisting (no pun intended) something, locks the nut, and say's "That's it."
 
LexTR3 said:
Getting back to carbs for a moment....
Click to expand...
Just a thought, you might want to start a new thread for each different topic. You'll get more attention that way, and others will be better able to find the information they are looking for. (Some folks actually read what has already been posted rather than asking the same question again.)

Ok, so here's a copy of the diagram. Right click on the link and open it in a new window, so it's big enough to read. (Never have understood why this forum limits photos to half of my screen width, but it does.)
https://i258.photobucket.com/albums/hh260/TR3driver/Manual%20pages/GS.jpg

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]I assume the rest of this sentence means loosen the locking nut on the jet needle, take out the jet needle, and insert the little pin that comes with the kit and tighten.[/QUOTE]Yes, except it's a screw (#6) rather than a nut.
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]
2. "Lower (or remove) the jet to the lowest position and slacken the jet locking nut." Not sure of the procedure or sequence here. How do you lower the jet, and do you do it before you slacken the jet locking nut?[/QUOTE]To lower the jet, disconnect the choke return spring #28 and pull down on the jet #9. There should be enough play in the linkage to get the jet down far enough. Otherwise you'll have to remove the linkage. Sequence doesn't matter here; but in general the first thing mentioned is to be done first.
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]
The only illustration shows a hand pushing down one of the tubes that come with the kit into the piston, but the illustration shows the suction chamber and piston back in place. Is this how you lower the jet?
[/QUOTE]
No, that's later, while doing the centering.
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]
3. "Refit the chamber and piston." Now or earlier?[/QUOTE]
Now.
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]
4. "Slide the centering pin into the jet bearing and tighten locking nut." I assume the centering pin slides into the upper jet bearing as you are refitting the chamber and piston.
[/QUOTE]
That is the theory. If it doesn't, you may need to tap the jet housing around a bit until it does.
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]
5. "If the piston cannot be moved with the centering pin in the jet bearing, slacken the locking nut again and repeat until the centering pin can be moved in and out of the jet bearing." If piston cannot be moved up and down... OK. Why would the centering pin keep the piston from moving? Rubbing on the inside of the jet bearing?
[/QUOTE]
Yes, exactly. And it would rub because the jet bearing was not centered to the piston, which is what we are trying to achieve here.
<div class="ubbcode-block"><div class="ubbcode-header">Quote:] Does the locking nut cause the jet to canter to one side or the other? How would repeating this procedure give some other result?
[/QUOTE]The jet bearing does move around a bit as you loosen and tighten the nut. Again, you may need to give it some encouragement with judicious tapping.
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]
6. "Check if the needle is bent by rotating the piston in the suction chamber." But no mention or replacig the needle. I assume you replace the needle between steps 5 and 6.
[/QUOTE]
Right. This would be done with the chamber off of the carb, the centering tool removed, the needle inserted in the piston (shoulder flush with the bottom) and the setscrew tightened. The piston should spin easily on the shaft, so just watch the tip of the needle as you turn the piston. If the tip moves in a circle, the needle is bent and should be replaced.
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]
If you have better, clearer instructions, and have a few moments to include them here, I would very much appreciate having them. [/QUOTE]
I have never had much luck with the centering tool; it seems to leave the jet off-center enough that the needle still rubs lightly. Maybe SU thought that was OK, but if the needle rubs, it will eventually wear both the jet and the needle, which leads to some very frustrating problems with overheating and potentially even severe engine damage.

So, what I do is to remove the mixture nut & spring (20 & 21) and reinsert the jet until it pushes the piston up. If the piston is touching the end of the jet, then the jet is perfectly centered. If it isn't, look carefully at the exposed needle to see which side of the jet it is rubbing on. Loosen the nut slightly, and tap the jet housing that direction. Lower the jet, tighten the nut, check again.

It is a trial and error process, since you have to loosen the nut to tap the jet housing and then the housing tends to move when you tighten the nut. But usually after 3 or 4 tries, I can get it right.

Afterwards, of course, remove the jet again, install the nut & spring, insert the jet, reconnect the linkage, etc. and finally readjust the mixture.

But if you're lucky, you won't need to go through all this. The click when the piston lands indicates the jet is centered well enough, so check for that before attempting to recenter.
 
Randall,
As I've said all along... You ought to writre a book. I would be the first in line, and the line would be long.

Your instructions clear up my questions about the SU instructions. It looks like something I can do with care and patience but not too much trouble. These procedures are new to me, so I'm agthering all the information I can before trying them, but after a while I'm sure they will be second nature to me.

The symptom that has led me to this point is that the rear carb falls freely and lands with a good click, while the front carb falls more slowly and falls with a clunk. I don't know if it makes a lot of difference as long as the piston falls and makes a noise, but I'm in the dark here.

It's possible also, from what folks have said on this Forum, that the pistons were swapped when I had the carbs rebuilt a year ago. I'll probably start with that procedure, check it out, and then decide if the problem is with an uncentered jet.

After I try these procedures, I'll start a new posting because I think others will be helped by what you and others have generously contibuted here.

Wish me luck.

BTW. All of these postings were "inspired" by one symptom: a sooty #1 spark plug, which started being "sooty" unexpectedly at one moment and ceased being "sooty" unexpectedly at another moment. The only thing I did between "sooty" and not "sooty" was to balance the carbs and readjust the mixture. But in the process, I discovered that one of the carb pistons was falling at a diffferent rate than the other.

It's either a winding path or a "slippery slope" that I'm on. Ha, ha.
 
Back
Top