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MG Midget and Sprite Technical - Mystery carb tube

I went to our annual All British Field Meet on Saturday and there was a 1960 Frogeye with something attached to the front carb that no one knew what it was. It was a thin tube about the size of the vacuum advance tube that was attached to the rear of the housing toward the bottom rear side. It then went back under the rear carb and at the end was a bulb of some kind that resembled what is at the end of a temperature sensor. It had a mounting bracket but was not attached to anything, free floating. The owner had gotten the car a month ago from New Jersey which is 3000 miles away and it had not been driven for 30 years. He had gotten it running and now is starting a list of what it needs which is a lot. That little mystery part was the only thing none of us could help him with. I hope my description is enough for someone to tell me what it is. Any ideas?
Martin

A picture would have been useful but it sounds like the vacuum advance tube that is attached to the distributor at its other end.
Alan Anstead

Unfortunately a picture is unavailable but the attached Moss view should show you where it is (the arrow points to where it is attached the back side). And it doesn't seem to be the vacuum advance since it comes out on the side opposite of where the normal vacuum advance does, near where the jet is. And why would it have what looked like a sealed bulb on the end with a mounting bracket. The examination was done with the bonnet up on a cloudy day so I couldn't really tell you much more.


Martin

Hi Martian,

The sealed 'bulb' was on earlier vac advance pipes and was designed as a flame trap, not sure if it was used on Frogs but Morris Minors etc had them on the earlier cars - not sure when they dropped the idea.

The pic is one I found on the net.

R.


richard b

12H733 used on Bs, Spridgets and as Richard has put Minors.

Can't get a decent image of it.



Nigel Atkins

That’s a similar image to one I found earlier, but was unable to capture it on my i-can’t phone.

A35s had them, too.
Dave O'Neill 2

Could be. It looked like the one in Richards picture but it ended at the bulb. There was no tube coming out of the other end. But since the car had been sitting for 30 years, there's no telling what has been done to it.

Thanks for the replies.
Martin

The mystery gets bigger, I understand Martin to be discussing a tube on the carb but pictures all are referring to the dizzy device.

Please make allowance for my disgraceful memory these days, I really have forgotten more than I now know so following the discussion gets complicated.

Martin was the tube from the manifold side of the carb?

I'm not making it out from the diagram but that 'take-off' looks as if it deals with jet overflows or seepage.

Flame traps seem likely but not if it isn't related to the dizzy.

Could it be.... ?

Mystery huh.
Bill sdgpM

Bill,

The tube was connected to the rear of the carb at the bottom. And though it looked like the one in Richards picture, the end away from the carb (right side in Richards picture) it was more pointed. And there didn't seem to have had anything attached to that end. This is all from the confines of under the bonnet on a cloudy day which means is was dark under there.

I'm sure this confuses things even more.
Martin

At least we are looking in the right place, on the left.

:)

Seepage or drip control mayhap, don't recall coming across anything similar on UK Moggies or Sprites.
Bill sdgpM

1959 Mini (Morris 850) engine bay screen shot.



Nigel Atkins

Nigel A.

That looks like it except that this one went towards the back. And the tube to the dizzy was missing. Different plumber?
Martin

Nigel that one is the vacuum tube to the Mini's advance retardy thingy, maybe the Sprite version of same went below and behind the engine to get to the dizzy.

Wish we could get a picture of what Martin was seeing.
Bill sdgpM

If it were one of those, but with the pipe between bulb and dizzy missing one would be able to feel either the broken end of the pipe, or a rough hole in the end of the bulb thing with a finger, even in poor light. Or pitch dark!

I wonder if it was some sort of aftermarket device designed to compensate for pressure changes which can affect SU carbs when run at higher altitudes. Is New Jersey hilly?
GuyW

The end of the bubble came to a point and didn't feel like it had a broken end. And New Jersey isn't hilly, the heights point, aptly named High Point is 1800 feet.

I'll try to get in touch with the owner to get a picture but it'll be through someone who knows someone who knows him. Saturday was the first time we'd met.
Martin

The early 948 Minor I had once had the vacuum pipe running round the rear of the engine.The carb was an H1 and had a connection for the tube at the bottom as described. The anti-flash bulb was held by a bracket attached to the heater tap. The tube was screwed into the vacuum diaphragm Its possible that the Frogeye has a Minor engine installed and the twin carbs refitted
Bob Beaumont

I had a 12H733 which I thought I might use but never did, I remember it as both ends just being open without a union but my memory isn't the best.

I remember the route being behind the back of the engine and with a bracket - but I might have remembered wrong.
Nigel Atkins

It could be a temperature compensation device. I've seen something similar to what you describe attached to older American carbs.
Never seen one on an SU though.
SUs mostly used bi-metallic strip compensators if anything, and later on Waxstats, but the general idea is the same. To alter the jet position relative to the needle in response to temperature.
If that's the case the carbs ought to work fine without any, like Waxstat carbs do if you replace the Waxstats themselves with washers. Just need to compromise a bit more on mixture settings.

Of course, that's all speculation and maybe complete bollocks, but it's all I can think of from the description.
Greybeard

Oops sorry I thought the electronic nanny would edit the slight profanity.
Greybeard

Just keeping this alive since I found out this morning that the owner is currently in Ireland but will get some pictures as soon as he gets back.l
Martin

This thread was discussed between 23/08/2021 and 28/08/2021

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