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Hello everyone. I am new to this thread. My girlfriend recently inherited a 1967 T120R. We had it serviced recently to get it up and running again. When it came back, it was running great. However, being the idiot that I am, I messed with (what I believe to be) the throttle stop screws because I wanted a little bit of a different idle.

Now, I cannot get it to idle if I'm not barely on the throttle. I know nothing about these bikes, and was wondering if someone could give me a process to reset these screws? Because the carbs were tuned and running well, I just nervously messed with them and now made them worse. Thank you for any help.
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Hi James. Best ask on the Classic forum
Carbs are black magic to me, I had a T140 and it confused me greatly. I hope she isn't giving you too hard a time over messing her motorcycle up :)
 

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Hi James
The problem you have is that you now have no reference point for the carb settings, to balance between left and right carb once you have turned the screws.
1) On the back of the carb there are two extension trumpets if you gently unscrew these you will be able to see into the back of the carburettors.
2) If you twist the throttle you can see the two air slides lift, make sure that you have about 1/16" free play on the cables before the slides move.
3) Get two pieces of thin stiff wire (gas welding rod is ideal) about 5-6" long, and wedge one of them under the cutout in the back of each carburettor slide. So that the rods balance on the edge of the carb, but are stopped from falling by the end tucked under the slide.
4) Now unscrew the idle speed screw (marked on your picture with the yellow arrow), the end of the rod should lift as the slide lowers. You will reach a point where the rod stops lifting as the slide is fully down.
5) Turn the screw very gently backwards and forwards, until you find the point that the rod starts to drop.
Do this for both carbs.
You now have a lower reference point where the setting is the same for each carb. Make a note, or mark on the carb of where the screw slot is, as you will use these references to set the idle speed.

Before you set the idle speed it might be a good idea to check the balance between the cable settings.
very gently open the throttle a tiny amount (1/64" or less) and watch both metal rods, if one rod twitches before the other then slacken the throttle cable adjuster for that side, until both rods start to move at exactly the same time. The cables are now set.
Remove the metal rods and screw the trumpet extensions back on.

Go back to the adjuster screws, making a note where the screwdriver slots are, turn the screw on each carb in exactly one turn. From now on when you turn the screw on one carb make exactly the same adjustment to the other carburettor, make a note each time you move the screw as it is easy to get confused where you are in the adjustment.

In your photo there are two other adjuster screws, this is the air/fuel mixture at tickover, if you have been playing with them, then screw them very gently in until they stop, then screw them out 1 1/2 turns each.
If you have not previously moved them then leave them alone, as the bike was running fine before.

Now these old engines are not good at idling when cold, so you will need to make a basic adjustment now and another fine adjustment when the engine is hot.

The golden rule is: If you move one adjuster screw, you must move the other adjuster screw exactly the same amount.
5) Start the engine and rev it with the throttle for a minute or two to get it warm, then lower the throttle. If the engine dies, screw in each adjuster 1/4" of a turn.
Start the engine and try again, if it dies, screw the adjusters another 1/4 turn. If the engine revs to high back them off 1/8 of a turn.
You will get to a point where the engine will sit at idle ticking over nicely. About 1000rpm
With Triumphs I like to have the tickover speed on the high side, as this helps maintain good oil pressure at idle.

6) check your throttle clearance on the cables, after all of the adjustments you should have about 1/16", if you have to adjust the cables again, make sure that if you adjust one cable, the other has to be adjusted exactly the same amount.
Here I like to put the rods back in, and just double check if they start to move at exactly the same time , the opening of the throttles together is key to smooth running around town, also if they are out one cylinder is doing the majority of the work pulling away, this is not goo

7) Go for a 10 mile ride and get the engine hot, when you get back home if the tickover has speeded up, back each adjuster screw off by exactly the same amount until you are back to a good tickover speed.

It is often a balancing act between too high speed hot and stalling cold, On these old machines.

good luck
Peg.

I thought I had better add, this is quite a good way to get a base setup, you can fine tune further By setting the ignition timing, Setting the valve clearances, tweaking the carb balance using vacuum gauges and fine tuning the idle mixture screws. But that is a whole new post.

the reason I prefer this as a basic set up compared to other methods, is not only do you set the tickover screws, you set the throttle cables as well, so it is a double win.
I always fine tune with vacuum gauges afterwards, if I am able.
 

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(................goes off and bookmarks Peg's post so that I can set up the new Amals on my 72 Daytona when the rain stops and the suns comes back, in a couple of months.)

Make this a sticky someone?
 

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Interesting...I do the 'one carb at a time' method. So some differences.
I use a dummy plug and a jumper lead for the spark plug lead that is pulled.
 

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This brings back memories. I used to have a ‘64 Bonnie with a ‘67 engine. If you don’t particularly love the carb adjustment challenge, my advice is to let a pro do it for you. You can easily lose half summer’s worth of riding days with an ill-running bike if you DIY. Anyway, enjoy the bike - it’s a great ride!
 

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Welcome to the forum!

An easy stop-gap till you get it properly tuned is to get it started and blip the throttle to keep it lit.

Then, slowly slowly turn one of the thumb screws IN until it will idle without blipping the throttle.

Next, turn the other one in slowly till the idle starts to rise.

Now turn the first one OUT just a touch. If it starts to die, turn it back in.

Idle (tickover) should be around 1,000 RPM. DO NOT idle the bike much lower, even if it "sounds cool". That will be starving the engine of oil when it is most needed for cooling.
 
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