British-Cars.org

Welcome to the DMR Site for British 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 - Carb Spring Tension

I have posted this question on the Y-Type forum without any response, so I am hoping some folk here may be able to help me.

Does anyone know what tension should be applied to the twin carburettor shaft return springs on YT's (or TC/TD/TF in this forum)?.

I've searched all the manuals and the website, but can't seem to find a suggested setting.

I had mine set with 180 degress of tension, but it often does not return to idle after an extended high RPM run, but sits at 1200 RPM until I "blip" the throttle - then it settles to 600.

I have found some wear in the shafts & body, so they will be re-bushed next week, but what is the tension needed when it all goes back together ?.

cheers

Tony
A L SLATTERY

Tony, it sounds as if you have a 'stiction' problem. Something seems to be preventing the throttle from fully closing. Try a bit of oil at the bushings where the shafts go through the carburetors. Any chance that you have a loose butterfly in one of the throats? Bud
Bud Krueger

Tony,

I've never seen a spec published for the initial setting of a throttle spindle spring. I generally never exceed a 1/4 turn at clossed throttle, and most likely use 1/8 turn. Remember, the spring winds up as the throttle is opened. Too much initial adjustment will cause a lot of wind up, and the force won't all be in the axial direction. Some of that force will press the shaft into the bushing, and accelerate shaft to bushing wear.

This is a fault that is often attributed to carburetor set up when in fact, it is a lack of oil or presence of dirt on the advance weights of the distributor. The weights stick slightly advanced, and the idle increases in sympathy.

For those who run both T-Series and later MGs, When seen on an MGB or MGA, it is sometimes the fault of the cable fraying inside the cable housing due to a bend or obstruction in the housing. Replacing the cable housing and cable solves the problem.

warmly,
dave
Dave Braun

Your problem may be due to the worn shafts and air leakage, and not spring tension. The new shafts should rotate without any bind. I don't remember turns or degrees for the spring, but it has to adequately snap the throttle shaft/plate shut. Don't overdue as Dave says. George
George Butz

I would go with George Butz's explanation. Worn carb bodies and throttle shafts often cause erratic idle speeds in my experience. Spray some carb cleaner around the shafts where they enter the carb body and see if your idle speed changes which is an indication of a vacuum leak at the shafts.
John Quilter (TD8986)

Tony,

I have 2 more things to add to all of the above.

Check that you have the springs correctly installed. They are handed (left and right hand) they should be installed so that when the throtle is opened they should reduce the diameter. if this is not the case then swap them.
Also check that the two shaft couplings are not distorted, if they are it will cause erratic movement.

John

52 TD

J Scragg

Thanks everyone, you have pretty much confirmed my thoughts & suspicions.

The application of a full half turn of tension was likely done to overcome the "stichion" of the slight wear in the shaft/bodies, and an attempt to close the now mis-fitting throttle disc.

The extra tension will have accelerated the wear without doubt.

When the bodies are returned with the new shafts, I will put the minimal spring tension (say 1/4 turn - thanks Dave), to keep the throttle light and minimise the future wear (the springs were correctly installed John, but thanks for the tip).

There was also a mis-alignment of the spindle shafts between the carbs - a little file work on the mounting holes will result in the shafts being properly aligned.

So as usual, it was a combination of little issues that created the "fast idle" problem.

Thanks again to all who helped - Safety Fast !
A L SLATTERY

This thread was discussed between 01/10/2011 and 04/10/2011

MG TD TF 1500 index

This thread is from the archives. Join this live forum now