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MG TD TF 1500 - Adjusting the SU's


It seems impossible to adjust the SU's on my '52 TD
If I screw the jets all the way up to their maximum, it seems as if the engine still runs far too rich: black smoke and black spark plugs.

I found a thread on this in the archive from 1997 (Joe Holtslag).Than it seemed that other needles could do the trick

Any idea's/experiences??

Thanks in advance

Erik van Hardeveld
Erik vanHardeveld

Wrong jet/needle combination??
Needle not exactly concentric with the jet??
Vacuum piston not coming down fully on the jet bridge when engine is ticking over??
Slow movement of the piston on higher rev's...
Four things which come up quickly in my mind ???!!!
Good luck, Nick 52TD/63midget.
D.G.J. Herwegh

Hi Eric, ---- I found that when you can't seem to get the adjustment lean enough, it turns out that the "glands" on the jet are leaking. Replace them with the original type cork soaked in oil or with the newer type "O" rings. But the "O" rings must be made of Viton (spelling?).Seems the usual type "O" rings are effected by the fuel (US) and swell up and fail. Try this after all the things suggested by Mr. Herwegh have been checked. Good Luck,Bob
Bob Jeffers

Spring has finally arrived in Rockburn. As soon as I saw 2 T's go by yesterday, I decided it was my turn in this lovely 22-degree weather - windscreen down, of course.

So last night, I decided to give 'er a wee tune up, cleaned up the pistons and needles, and checked the seals (as Bob had suggested) and set the mixture and idle and cranked 'er up. Sounded great. Let it run for about 10 minutes, Shut it off and went to bed.

This morning, fired it up and it was running quite lean. Let 'er run for 10 minutes and it only got worse.

In desparation, I wiggled the buttefly shaft, and after 50 years, it came as no surprise that it is quite worn, and no matter how often one tunes it, its going to go 'off' as air will always leak past it causing it to run lean.

So there's one more thing to check in your tune-up.

Now to go out and mix it up with the Harley's!

Gord Clark
Rockburn, Qué.
Gordon A. Clark

I would think in the Netherlands you are close to sea level, or less than 300 meters high. So the standard needles should be fine.

If you have your needles incorrectly installed in the pistons, (too high) won't that make the mixture impossible to adjust? I would think a loose butterfly shaft (rebushed mine in 1989) would cause a lean running condition which would be difficult to make idle.

I like Bob's suggestion though, with all the oxygenated fuels around (alchohol) the rubber in the glands could be affected. When I rebuild my carbs I think I'll check that as I always run slightly rich. It's amazing what you will put off checking when you know "one of these days I'm going to restore this thing" lol.

D. A. Braun


Thanks for all your help; this is a wonderful way of
gathering advice from all over the world.

I will buy new glands and soak them in oil before fitting; I did that with the bigger ones, but not with the small.

I will also polish the jets and check the needles; I the needles are ES which I think means "standard"

Thanks again

Erik vanHardeveld

I had that problem and I solved it using EW needles. Others have confirmed my choice. I may be the one who stated so in a 1997 thread.

1950 TD
Denis L. Baggi

While you are waiting for the jet glands check the float lever setting. With modern fuels use a 7/16" bar.
John James

g.h kings

Most of the time if you are still running too rich when the jets are screwed up tight, the floats are too high.
Lower the fuel level in the bowls by bending the float lever. The clearence should be 3/8 in for early SU's and 7/16 in for later and 1 1/2 in SU's. The workshop Manual has a typo on this setting.

Many have found that our "new" fuel is less viscous and will run so rich that it cannot be adjusted and the float level must be lowered. (3/8 to 7/16, 7/16 to 1/2).
Don Harmer

Hi there

Thanks again for all your comment and interest.

I'll also try lowering the float level and let you all know the results.

Erik vanHardeveld

This thread was discussed between 17/04/2005 and 18/04/2005

MG TD TF 1500 index

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