MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG TD TF 1500 - Mystery Control rod - carburettor

I am working on checking the balance of the 1.5in carburettors for the TDII.
The rod in the image joining the choke levers to the carb body is on the forward carb but nothing in the same plce on the rear body.
It appears to prevent the choke lever pulling down the jets.

Is this rod correct for this setup, and what is its purpose.

Your wisdom and advice will be much appreciated.

Ian Bowers

It is the fast idle lever and arrangement, standard on the 4031 carbs on a Mark II TD. As the jet arm is pulled to the left by the enrichener cable, the rod rises, and speeds up the idle.

One carb, through linkage, speeds up both carbs.

Tom Lange
MGT Repair
t lange

Thanks, Tom, now I will go and see if it is doing what it is supposed to!

At the moment the pulling choke cable moves nothing!
Ian Bowers

Sorry - Or does it work the other way, on a fulcrum principal - the rod moves down, and lifts the lever?

I can send photos of my carbs later today, if needed.

Sorry. Tom lange
MGT Repair
t lange

To my understanding this rod connects the choke mechanism with the throttle: once the choke is pulled, the throttle opens a little bit (adjustable by that srew on top of it).
When the engine is cold, you need a rich mixture to start. And a fast idle. And that's why those days engineers invented that connnected rod to do just that. Man, they were sooo clever!
Huib Bruijstens

The rod moves down and pulls the fast tickover lever off its adjuster screw as the jet moves down.
Ray TF 2884
Ray Lee

Thans for the very useful clues.

Certainly the rod is set to puls a lever down to raise the choke control screw.

The thing I still can't get to perform is that the rod is immovable. I can raise the lever by hand, but get no movement when I pull the choke cable. The whole rod structure linked to the jets appears solid, though the jets meve easily when disconnected from the linkages.

Strange.
Ian Bowers

I never really liked that set up as it was designed so as soon as you pulled the choke knob you got both fast idle AND enrichment. I modified mine with some parts from a Triumph TR3 carburetor so that it permitted the first quarter inch of choke cable travel to raise the idle only, then further movement caused the enrichment. Very useful during warm up to just increase the idle a bit. Many SU carbs work this way.






John Quilter (TD8986)

Ian,

The setup you show in your picture is incorrect and may, or may not work. It is missing the idle speed adjusting screw. On the throttle shaft lever you should have two tapped holes, one for the idle speed and the other for the fast idle. In your case the fast idle screw is used for both functions. To correct this you need to add the missing screw, balance the carbs, adjust the fast idle screw to have about a 1/16" clearance between it and the lever.


John


J Scragg

If you have good eyesight or blow the pic up, you can just see the other adjuster hiding behind the fast idle. (I think)
Ian, you may already know that the 4031 carbs are not dustfree type and need a vented damper rod cap, The transfer port in the bell is not drilled.
Ray TF2884
Ray Lee

Ray,

You are right! After zooming in I can just see the second adjuster, well hidden behind the other.

John
J Scragg

I can confirm that both adjuster screws are in place and working, also the cap is vented and clear.
It is simply that the adjusting rod from the choke lever is rock solid, though the lever on the carb body it is attached to moves freely.
Also the choke cable moves freely. I suspect that something in the linkages is not attached in the way it should.
Unfoirtunately I am away from the car for some 6 weeks but will have a further go at resolving teh isses on my return, and will take full account of your advice on my return.
Ian Bowers

Is the choke link connected to both carbs? I looks as though the jet clevis is held off and not full butted up to the adjuster nut. If you take out the nice shiny split pin on the bottom of the rod it should come out out of the choke lever easy, if not it is probably bent and fouling on the body.
I recently renovated a pair of TDC carbs and the rod was bent so much it was holding the carb open with the main idle screw not touching the body.
Ray TF 2884
Ray Lee

Ian - please contact me off-line at tlange@acadia.net

Many thanks.

Tom
t lange

I can't recall ever having this issue with SU carbs. On my TD, the idle adjusters are set at 1 1/2 turns out, but the fast idle adjuster, even fully turned down is at least 3/16" from the throttle plate so no fast idle without enrichment. These are brand new carbs so no one, myself included, has "worked" on them.
W Worden

This thread was discussed between 28/08/2021 and 11/03/2022

MG TD TF 1500 index

This thread is from the archives. Join the live MG TD TF 1500 BBS now