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MG TD TF 1500 - 1952 mkii carb rebuild ??'s

I am replacing the 1&1/4 carbs with 1&1/2 inch carbs that have the proper markings showing that they are the correct carbs (thanks to hugh pike)for a mkii. I am having some troubles that will require learning how to set the floats and jets. I found a good writeup in the mga archives from Don Trembly "su jet assembly tips" on using a dial gage so will try to learn how to do it. In the meantime a few questions:

Will someone please describe what a thrust washer looks like - goes at the bottom of the spring inside the piston chamber. Can't believe it would make a difference but who knows.

Skip Burns' article says a mkii needs red piston springs but Moss sent blues ones for a mkii. Is there a real difference so that I should reorder?

Last for now and very puzzling - after running the engine for a few minutes the carb nearest the driver gets cold - cold to the touch. After ten to fifteen minutes condensations builds up on the carb body and drips off and the piston chamber is also cold. Front carb does not do the same. Any ideas?

As always thank you in advance.

Tim


tw hager

Tim,

The thrust washer will help keep the spring from digging into the piston, it is just a plan washer with an I.D that fits around the dampener chamber and an O.D that fits inside the cavity. If you have brass, or aluminum pistons with weights bonded to them, you don't need springs. But the red will work.

If the rear carb gets cold, and condensation forms, but the front doesn't, you are running more air through the rear than the front. You will need to re-synchronize the airflow, so both carburetors draw evenly. Use a unisyn, a pair of whiskers in the dashpot chambers, or a rubber tube to listen to the airflow, but they need to be adjusted independently of each other and then lock the throttle shafts together.

Warmly,
dave
Dave Braun

Dave
As many times as I have balanced the carbs with a unisyn over the past couple of days, am almost positive that they are balanced but will check tonight before I start again. You and others are always such a help - thank you very much. I still do not have everything adjusted yet so I may have more questions later.

tim
tw hager

Dave
I was thinking on the way to work that since I am having problems with the adjusting nuts ie no response all the way up, that could very well be the issue. I will try to get the floats set and mixture set this week.

tim
tw hager

Tim- This is a dumb question but when you switched to the 1 1/2" SU's did you open up the inlet manifold openings from 1 1/4" to 1 1/2"? This is a fairly easy operation but would need a vertical mill to accomplish.
Roy Challberg

Roy
they came with the correct manifold that attaches to the head and I have had the air cleaner manifold drilled for the carbs but it is not on yet.

tim
tw hager

Tim,

To balance the carbs, my approach would be to dial them in at about 1300-1500 rpm, get them balanced, and then lock the shaft. At that point I turn each adjusting screw exactly the same ammount to lower the rpm to between 650-850 rpm. I use an analog dwell-tach to read rpm.

As for adjusting the mixture, if you can't get them lean enough, it is almost a certainty that you have poorly centered jets, and are hanging up the needle, or it has worn the jet and the needle to the point that they are too rich. It takes very little wear or hung needle to make the mixture too rich at idle. Also, make very certain that your jets are returning to their starting point after being enriched with the 'choke' cable.

warmly,
dave
Dave Braun

To add to what Dave said,if the jet seal is worn or dried out, vacuum will suck fuel past and you will never get it lean enough. Some aftermarket rebuild kits, in the past, used rubber instead of oil impregnated cork jet seals. If someone used these in the past, they could be the culprit; especially with today's ethanol blended gasoline. A great source for proper seals and components is Joe Curto. http://joecurto.com/
Steven Tobias

1952 TD/C 14306 (Mark II) -

1. What does the 1 1/2" in the carb designation/sizing refer to? I have the proper Mark II car number scheme, dual fuel pumps, (3) extra Andrex dampers, and assume the 1 1/2" carbs, but see that the opening into the carbs only measures 1 3/8". The pistons are very close to 1 1/2", and I would guess that measurement is what makes them 1 1/2" versus the standard 1 1/4" SUs. Is that correct?

2. Based on a previous post in this thread, do I need to ream out the air intake openings to a full 1 1/2"?

3. My "MG midget" workshop manual shows the float chamber's "forked lever" adjustment measurement to be 3/8". The "SU Carburetters Tuning Tips and Techniques" book's Type H, Figure 31 shows the adjustment measurement to be 7/16". Which is "right"?

Thanks!

Mike in Los Angeles, CA
Mike Palatas

The size of SU carbs is the outlet diameter, the inlet diameter is normally 1/8" smaller, although the Burlen/SU reference catalogue does not make this clear.
R WILSON

Tim,

Go to the manufacture Burlen Services, the SU web site is www.sucarb.co.uk, they show LS1 needles with red springs for a TDC (MK2), the same spec engine in a TF used GJ needled with blue springs.

Bernie
B W Wood

This thread was discussed between 15/08/2010 and 10/10/2018

MG TD TF 1500 index

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