Starting Carb water feed pipe alignment

Hi Is there a trick to getting the pipe from the engine back into the starting carb, See pics when I offer up the carbs and hang them on the studs this pipe does not seem to anywhere near the inlet of the starting carb, tried taking it off and screwing it into the engine first but it looks like it way out of line also
method or tricks appreciated or have I got something wrong


Hello Mike
Others will know better than me, however, firstly, on our 3.5 Litre MKIV engines, it is not a water pipe, it is connected to the inlet manifold and provides a vacuum for the Starting Carb’ to operate.
On our cars is screwed directly into the head ( without the aluminium adaptor) and has to be aligned horizontally and at approximately 90 degrees to / from, the head, this can allow the fitting of the starting carb’.
In your case, may be easier to remove the three setscrews on the aluminium adaptor, fit to the stating carb’ and then re-install on the head.
The small pipe (1/4 inch) protruding from the brass fitting, I would guess would have been installed to allow the fitting of a vacuum operated distributor or vacuum gauge / tester.
Trust this is helpful.

Hello Mike, the pipe which is causing you the trouble is the Starting Pipe. The Starting Pipe delivers the starting carb extra fuel and air mixture for enrichment when engine is cold.

For Mark IV 2 1/2 litre engines the Starting Pipe is part 925/A as called out on page 9 of the 46-48 parts manual. This same pipe is called out for the Mark V 2 1/2 litre engines on page 10 of the Mark V parts manual. Page 22 of the Mark V parts manual calls out for the 3 1/2 litre engine part number 1469/B.

There is no parts plate for the 46-48 carbs in the 46-48 parts manual I have. The Mark V parts manual shows the 925/A and 1469/B side-by-side in plates E and M.

In the Plate E drawing for 925/A, one may see it does not readily appear to match your photograph of the tube you have. The Starting Pipe angle bend in your photo appears more to my eye to match the 1469/B. Also, neither Starting Pipe in the plates shows the small pipe with hole centered on the outside of the engine attachment point as appears in your photo.

It is true alignment of this part is slightly tricky on assembly for the 3 1/2 litre engine so I suspect that will be true for you as well. However, maybe you should verify the correct part is in your possession as a “starting” point. Maybe you have the correct part and my perception from the photo is off. At any rate, that small pipe seems incorrect. Maybe you can do a photo more from the side of the Starting Pipe to show the views as seen in the parts manual plates.

One trick for getting the Starting Pipe aligned is to use just a touch of a pipe compound in the block threads so the tube does not have to be really tight. If I recall correctly, the threads into the block are tapered so the pipe does not have to be overly tightened to have good seal. This slight looseness is needed for rotation of the Starting Pipe to fit where the starting carb will offer up to it.

Also, the starting carb can be rotated relative to the main rear carb on its mounting.

I think the answer is to attach it to the carbs before offering them up the head and have the starting carb slackly attached to its carb. Then locate the pipe in the head alloy piece as you are offering the carb assembly for fitting.


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One further point to aid installation is to consider which Starting Pipe end goes on which piece. I’ve got the one on my Mark V mounted with the funky cylinder end on the head side as in Mike’s photos and Rob has it reversed. If same fittings on both ends, a choice may be available.

As a detail, does anyone know why the funky cylinder end has such mechanical design? Is it just to achieve a 90-degree fit in tight space?

My pictures are of a 2-1/2 Liter.
Roger’s are of a 3-1/2 Liter.

Rob’s point to be aware of differences between 2 ½ and 3 ½ litre engines is good. For example, note the spacer between carb and head showing in my photo mid-center slightly left and slightly up from center, which changes geometry of Starting Pipe connection compared to if that spacer is absent. Mike’s photo shows a flange on the head which may push out the Starting Pipe by the same amount as the spacer for the Mark V.

For the Mark V 3 ½ , the Spare Parts Catalogue indicates the rear carburetter float chamber, which includes the auxiliary starting carburetter is:

Part Number 3258 Float-Chamber for Rear Carburetter Plate M.18

The part call out is the same for the Mark V 2 ½ except it is indicated as Plate E.18

For the 1946-1948 Mark IV, the Service Manual shows the 2 ½ and 3 ½ as using the same Auxiliary Starting Carburettor (Plate 2, page 19). Plate 2 shows outlet below solenoid is different than used in Mark V, although that same plate is shown in the Mark V Service Manual as Plate C.11 Starting Carburettor page C.15.

Also, carb solenoid and auxiliary starting needle assemblies use the same parts numbers for 2 ½ and 3 ½ on 1946-1948 and Mark V.

Unfortunately, the 1946-1948 Spare Parts Catalogue does not seem to call out the float-chamber for the rear carburettor. I can’t compare specific float-chamber part numbers with the Mark V.

Anorak note: “carburetter” is the spelling used in the Mark V Spare Parts Catalogue; “carburettor” is the spelling used in the Mark V Service Manual and both the Service Manual and the Spare Parts Catalogue for 1946-1948.

Well its all a bit embarrassing ! the pipe was simply mounted on the wrong end of the carbs, took it off turned it around and fitted it to the block and everything fits now, I had the carbs professionally restored and they came back with the pipe on the wrong way round, I just assumed it to be correct, just goes to show don’t take anything for granted, thanks for all the help
and my next question is ???

Forgot to post picture or reversed pipe

From an SU publication:

Being involved with British cars from about age 15, I learned to spell it with two “t’s” and I just can’t get spellcheck to realize it’s not carburetor, that’s only for Chevys Fords and Dodges. :wink: