Choke adjustment

[MT2+2]

Hi All,
The choke on my 1966 Series 1 4.2 triple SU car drops the jet and enriches the mixture immediatly the choke slider is moved upwards.
Can anyone advise how I can reset it as per the manual, such that the first inch or so or upwards travel of the choke lever, only opens the throttle, and well before moving the jet?
Will I need to remove the carbs to make the adjustment?

Im trying to upload a couple of photos to show the arrangement, which clearly show that the jet lever is already in contact with the mixture adjustment screw arm when the car is cold.

The car starts fine from cold, but I have to keep my foot on the accelerator for several minutes after sliding the choke back down, to avoid the revs dropping so low that it stalls. This makes driving reallly difficult, especially if I need to use the brakes!

I hesitate to start a new thread for such a simple question, but I havent been able to find any guidance on the forum about this. If Ive missed it, please redirect me!

Many thanks in advance,
Martin Thomas.

[abowie]

There are 3 sets of adjusters on the E Type SU to control idle and starting mixture.

If you have a look at the manual you'll see that there are fast idle screws that are a separate adjustment from the mixture screws.

There are also slow idle screws which allow a tiny amount of air to bypass the closed butterfly. These control idle when the choke is off and the car is up to temperature.

To set the fast idles correctly, get the car warmed up and idling properly using the slow idle screws ( the big ones). Make sure the choke is fully off.

Now, using a thin feeler gauge (I use a 2 thou one) open the fast idle screws and then close them down onto the feeler gauge so that when the feeler gauge is removed the screw is just clear of the actuator on the throttle rod. Do this for all 3 carbs.

Now, when you pull the choke cable the fast idle will actuate bringing the revs up.

[Doug Buchan]

"The choke on my 1966 Series 1 4.2 triple SU car drops the jet and enriches the mixture immediatly the choke slider is moved upwards.
Can anyone advise how I can reset it as per the manual, such that the first inch or so or upwards travel of the choke lever, only opens the throttle, and well before moving the jet?
Will I need to remove the carbs to make the adjustment?"

Hello Martin,

As you state, the throttle plate should be opened as the first stage and mixture enrichment thereafter.
This is accomplished via the lever, cam, rod & shoe and arm mechanism on the shaft on the jet diaphragm housing. The primary lever, cam and secondary arm which actuates the jet diaphragm lever are fixed with tapered pins. The jet diaphragm lever floats on the shaft unpinned.
I would inspect all three jet housing mechanisms for proper operation.
You only have to remove the tapered pin on the arm which resides between the jet lever and the entire shaft assembly can be removed

Regards,
Doug

[christopher storey]

To set the fast idles correctly, get the car warmed up and idling properly using the slow idle screws ( the big ones). Make sure the choke is fully off.

If I may just add to Andrew's advice, the idle setting using the big air bleed screws which he refers to needs to be accomplished with the throttles themselves fully closed, so make sure that the fast idle screws are fully backed off and not touching the cam

[abowie]

Christopher is correct.

The best thing for you to do is to loosen all 3 carbs' actuating rods, ensure that all 3 butterflies are completely closed and then retighten.

If you look at the actuating rod you will see that it is made of two separate pieces held together with a pin. This design allows a bit of slack in the mechanism, so that it doesn't move the butterfly immediately when the throttle rod starts to move.

It is important to set all 3 of these so that they all have a maximum and equal amount of slack, thus ensiring that all 3 butterflies open at the same time.

[MT2+2]

Many thanks all for sharing your knowledge which I am now digesting.
In the meanwhile, Ive attached some photos that show the middle carb when the choke slider is off, ie at the bottom of the slider. The screw in the foreground is the mixture adjustment screw.

[MT2+2]

<t>Just to clarify my question, the mixture has been set with a Gunstons CO meter and is fine, and I have adjusted the slow idle screw (the big one) with an air meter and she ticks over steadily when warm.<br/>
So the only problem remaining is that the choke enriches the mixture immediately the dashbord slider is moved, rather than half way up, as is should be according to the manual. <br/>
The car usually starts first time and runs very well overall.</t>