MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

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 - Choke on 1953 TD - How to check

Can someone tell me how to tell if my choke is working on my 1953 mg td? What should I look for on the carburetors? One website suggested that something should move by 1/4'.
Thanks-
Bill Chandler, Ann Arbor, MI
W F Chandler

Look at where the cable connects at the carbs and watch and see the lever move...that tells you it is correctly working...
RAK Kirk

The jet needles actually get pulled down out of the jets. You will see the clevis at the bottom of each carb being pulled down by the linkage. You should also feel the engine roughen up (assuming it is running) as the mixture enrichens. If the jet seals are leaking, and fuel is being sucked past them, the engine will be running rich all of time. So, if the needles are being pulled down, and the engine runs the same, you will most likely need to replace the seals. If you do, I would get them from someone like Joe Curto, who supplies actual S.U. parts. Some of the large distributers use short pieces of rubber tubing, rather than the proper oil impregnated cork.
If you need Joe's info, let me know, and I will find it for you.










Steven Tobias

Thank you both. I was told that on this SU H2 carburetor that the choke worked by pushing something up - thus opening the flow of gas. I am hearing from Steven that the bottom portion is pulled down - I assume opening the flow for gas.
I also read that it is better when starting in cold weather that it is better to NOT step on the accelerator, thus restricting the amount of airflow and enrichening the concentration of gas. Does this make sense?
My problem is that after the car sitting for several months it will turn over well, but not fire up at all. I added gas stabilizer in November. Do I need new gas/
Thanks,
Bill Chandler
W F Chandler

I just found a wonderful site that explains with very nice diagrams how the SU carb works:

http://www.roversd1.nl/sd1web/carburation.html

You are correct, the choke mechanism pulls the jet downwards, allowing more gas to get by the static needle. This allows more gas, but not more air.

I will take a look to see if mine are moving well with the choke lever pulled.
Bill Chandler
W F Chandler

There is also a linkage that opens the throttle slightly. See the attached picture. When the choke is pulled, the choke linkage moves in the direction indicated by the green arrows. The throttle is opened by the linkage circled in Red. (The red arrow points to the connection to the choke.) This rotates the throttle shaft as indicated in blue.

I hope this helps!
Evan

Evan Ford TD27621 EXL/NA

Evan--
Wow --that photo is incredibly helpful. Now I really understand the mechanism. Do you think it is better to start the car without pumping the accelerator when it is cold and you are using the choke?

Thanks,
Bill Chandler
W F Chandler

It cracks me up because my wife always pumps the throttle a couple of times before turning it over. She swears it starts better.
Reality is, since there's no accelerator pump on the SUs, no fuel is squirted in; all that takes place is whipping the butterfly open and closed.
You could add a slug of fuel by turning the key on, building up fuel pressure, and pushing the tickler down on the float bowl, but that's complicating life.
The choke will help start a decently tuned engine.
Jim Northrup

Bill, one of the things that these SU carbs don't have is an accelerator pump. The only thing that pumping the accelerator gets you is a tired foot. When the engine is cold you will probably want to pull the choke knob all the way out when you go to start. Remember that the linkage advances the throttle quite a bit. So be ready to push the choke knob back in a bit to avoid high rev's on a cold engine.

Best of luck --- Bud
Bud Krueger

Never pump a British SU equipped car....just get ready to add gas when it has started....
gblawson(gordon)

Thanks to all for your helpful comments--
photo of my car should be attached.
Bill

W F Chandler

Hey Bill, Nice car! Sorry, I just realized that I typed backwards. The needles are fixed to the bottoms of the pistons, which move up and down with vacuum; thusly adjusting the mixture on acceleration, eliminating the need for an accelerator pump. Really an ingenious design! It is the jets themselves that are fixed, and only move down along the tapered needle when the choke is applied. I actually don't know why we call it a choke, because it bears no resemblance to the conventional choke that is actually a rotating disk that "chokes" off air flow, in order to enrichen the mixture, in the more common carbs that most people are used to!
Steven Tobias

Just for follow-up. I took apart the linkage to the chokes on each carburetor and found out they were both frozen shut. I gave a brisk tug on the lever arm and both became free and with a little oil they work great. I shortened the choke cable and it works perfectly now. The car started on the first crank in 41 degree weather.
Thanks to all for your advice and photos - I could not have done this without the internet connections.
Bill Chandler
W Chandler

This thread was discussed between 24/02/2010 and 15/03/2010

MG TD TF 1500 index

This thread is from the archive. The Live MG TD TF 1500 BBS is active now.