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 MGA - Vacuum advance line confusion

While removing the carbs from my car yesterday, the thin copper vacuum advance line got broken in the vicinity of the flame trap. Looking at the line on my car, the pipe appears to have been "hand bent" at some point. and it's missing the larger bracket that I think attaches it to, or near, the intake manifold.

I checked out the Moss catalogue and was surprised by the price of the repro part. (It seems that the price of repro parts almost always surprises me). I'm going to have a crack at fixing my existing pipe, but I don't hold out too much hope of success, so I'll probably end up having to order a new one.

The questions I have are:

1) Is the shape of the vacuum advance line shown in the Moss catalogue accurate? (see item #24 here <A
href="http://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=29250">http://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=29250)

If that is actually how the pipe is pre-bent then I'm quite confused. Assuming that the small bracket (#28) attaches to the rear head stud, it seems to me that the distibutor end connector (#26) is pointing in the wrong direction. The carb end connector (#27) also seems to be pointing in the wrong direction.

2) The blowup diagram of the rear carb (see <A
href="http://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=29218#top">http://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=29218#top) shows item #103 as a vacuum line union (part# 378-240). I don't recall seeing anything that looks like that on my car. I believe the connector on carb end of the vacuum line (#27 in the vacuum line drawing) screwed directly into the carb body.

Can anybody help clear up my confusion?
Andy Bounsall

While removing the carbs from my car yesterday, the thin copper vacuum advance line got broken in the vicinity of the flame trap. Looking at the line on my car, the pipe appears to have been "hand bent" at some point. and it's missing the larger bracket that I think attaches it to, or near, the intake manifold.

I checked out the Moss catalogue and was surprised by the price of the repro part. (It seems that the price of repro parts almost always surprises me). I'm going to have a crack at fixing my existing pipe, but I don't hold out too much hope of success, so I'll probably end up having to order a new one.

The questions I have are:

1) Is the shape of the vacuum advance line shown in the Moss catalogue accurate? (see item #24 here http://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=29250)

If that is actually how the pipe is pre-bent then I'm quite confused. Assuming that the small bracket (#28) attaches to the rear head stud, it seems to me that the distibutor end connector (#26) is pointing in the wrong direction. The carb end connector (#27) also seems to be pointing in the wrong direction.

2) The blowup diagram of the rear carb (see http://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=29218#top) shows item #103 as a vacuum line union (part# 378-240). I don't recall seeing anything that looks like that on my car. I believe the connector on carb end of the vacuum line (#27 in the vacuum line drawing) screwed directly into the carb body.

Can anybody help clear up my confusion?
Andy Bounsall

Andy,
Not sure about the shape of the line but I do know that the new type of vacumn lines do not use a screw on connector. You are now supposed to cut off the end of your V/L and attach a rubber connector. This connector attaches to the dizzy.

Some suppliers are offerring new vacumn advance unit with screw on connectors, but they are very pricey.

Good luck with the other questions. Gordon
Gordon Harrison

Andy

There was talk about this last year so worth a look in the archives. The bracket actually fits to one of the manifold studs, not the head stud. Off the top of my head I am not sure if its the rear stud or the second one in. Fairly inaccessible though!

I actually have mine fitted 'incorrectly' to the rear brass firing order plaque stud. At least it is accessible there.

Steve
Steve Gyles

Andy-
The pipe can be soldered, with or without a sleeve at the break. Or join with a piece of rubber tubing. You're on our own if you want OE appearance, but this was covered a while back in the archives.
FRM
FR Millmore

Andy, for what its worth from this side I too had the same problem with a snapped off vacuum pipe. It had been badly fitted in the first place-- kinked at the moisture trap which was upside down and mounted on the end manifold stud instead of the next one in.
Local mg specialist who had engine out to replace gearbox said that vacuum pipe dropped off during engine removal and in their opinion was a waste of time anyway so they just plugged the carb. Have since purchased a replacement which has same number as the Moss one on your link (163-620) so presume it is a Moss one. Bends hopeless. Had to almost completely remodel it to get it anywhere near to fitting. It comes complete with the carb end male adaptor plus olive already on the pipe ready to fit direct into the carb.
The dist. end has a female adaptor which I have cut off to fit it to the dist. with the existing rubber pipe (which is actually straight not an elbow)as per Gordons comments.
David
D C GRAHAME

Thanks for the replies, but I'm still confused. The drawing of the vacuum line in the Moss catalog ( http://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=29250) shows a small clip (item 28, part# 153-820) as well as an L shaped bracket.

The L shaped bracket is missing from my vacuum line. The small clip was attached to the rear head stud.

Which bit are you telling me s/b attached to the 2nd manifold stud?

The distributor end of my pipe definitely uses a scew-on connector to attach to the vacuum advance unit on the distributor.

The other piece that's got me confused is, as mentioned before, item 103, part# 378-240, shown on the carb diagram and identified as a vacuum line union. What is that part all about?
Andy Bounsall

FRM, thanks. I plan to try soldering a sleeve over the break, but since the break is so close to the flame trap, I'm not sure how successful I'll be.
Andy Bounsall

It's the L-shaped bracket that holds the flame tube that attaches to the manifold stud.

Steve
Steve Gyles

Andy -Have a look at Clausiger page 56. This shows exactly where each bracket fits. OK so you have got an original dist. and you can use the female threaded end and olive supplied with the new pipe.(Items 25 and 26). I think item 103 is probably the same as item 27 which ,with the olive item 25, will screw directly into the carb.
David
D C GRAHAME

OK, now I understand. That photo really helps. Thanks very much.

I'm still curious about the "vacuum line union" shown in the Moss catalogue. It's pretty much impossible to tell from that line drawing what that part is. Could it be that the original vacuum line had a female connector on the carb end and that this piece shown in the Moss catalogue is come kind of male-to-male adapter?
Andy Bounsall

Hi Andy, When I originally restord my roadster many years ago, I had no idea that a vacuum line trap was even supposed to be in place , since the DPO had removed it and the feed pipe. I deduced that the vacuum advance unit should required vacuum to operate, and not knowing there was a fitting on the carburettor, simply drilled and tapped the intake manifold to accept a fitting with which to feed the vacuum advance unit. I ran my MG for about 10 years without a vacuum line trep with absolutely no trouble. I finally found out about the factory installed fluid trap on a well restored MGA at a car show, and eventually even fitted one to my vehicle. Of course it has not made any difference in the way my car runs, but is certainly a conversation piece. People who look under the hood always ask what the tiny cylinder is for! Good luck with your repair! Glenn
Glenn

Andy-
Most or maybe all OE MG had a threaded hole in the carb, with a seat for an olive, so there was a loose male threaded end on the pipe. That male nut was the single place that I ever used one size (0BA or 1BA)of my W/BS wrenches, nothing else ever used that size.
I have seen a male-male adapter as in the Moss book, with a female nut and olive on the pipe, but I could never figure out where they came from, or if they were stock OE on some models, or random fitting, or if it was a requirement for service carbs, or maybe service pipes, or a repair fitting for stripped out holes. The giveaway as to whether you need it would be whether the bottom of the hole is flat or drill point, or if it is contoured for an olive seat. The adapter is more common and OE on other applications, like Rover.
I've seen way too many carbs to keep all the variants straight!
FRM
FR Millmore

Well, my brain finally started, and I recalled that I have the complete SU parts listing for all BMC cars. It's a very big book and easy to get lost in, but it appears that for MGA, 1500 use the adapter and 1600 doesn't. Since the pipe is not an SU bit, that's where the trail ends. I now think that the male nut end does not use an olive, but is one of the long taper things where the nut itself acts as a compression fitting. Once overtightened, as they all are, the nut gets real tight on the pipe, making for an unpleasant removal experience, especially in the close quarters of an A.
FRM
FR Millmore

This thread was discussed between 12/03/2007 and 13/03/2007

MG MGA index

This thread is from the archive. The Live MG MGA BBS is active now.