Vacuum leak V12

[andrewh]

Chaps, I am just doing some work on my series one XJ12 and have a small vacuum leak on the rubber pipe that connects the two carburettors together. It doesn't appear that SNG list this pipe and as I am sure its the same on a V12 E, I wonder whether anyone can tell me what part number I need or a supply of it elsewhere. It has to be a really good fit or else when you open up the throttle it will suck air back through the aperture causing a cough. Hope thats not as clear as mud!!

[mgcjag]

Hi Andrew..have you looked in the knowledge base S3 parts catalogue...with lots of diagrams.. Steve

[andrewh]

No I haven't actually. Surely not self help Steve!!!???

[andrewh]

No I haven't actually. Surely not self help Steve!!!???

But I have now, part number 12861, exactly the same as the XJ12 as I thought, but not listed by SNG. Its just thick wall, to stop if collapsing in on itself, small ID rubber hose.

[mgcjag]

http://www.jagspares.co.uk/Manners/part ... =C12861%2A

[Series1 Stu]

You'll get a metre of pipe from eBay or similar for the same sort of money, post free too.

Make sure you get fuel resistant thick walled vacuum hose. It won't be a problem if you know the bore size.

That's all the specialists will do.

Regards

[andrewh]

yes I will try to find some on E Bay. Will measure up today, I just though someone may have found a supplier already. Thanks. As an aside and for the benefit of others. They way to establish whether this balance pipe is leaking air in is to have the car idling and spray a little carburettor cleaner on the pipes. If the engine speeds up then it is sucking air in . More noticeable under acceleration of course.

[MarekH]

This "balance pipe" - is it's purpose not to share the output of the choke between the two carburettors?

Given that the two carburettors draw air from the same airbox just a few inches away from each other and the manual tells you how to set and synchronise the airflow, there seems to be little point to having a simple balance pipe. The only asymmetry is that one carburettor has a choke and the other doesn't.

Put another way, make sure the hose is fuel resistant.

kind regards
Marek

[andrewh]

All I can say with total certainty is that it was sucking air through there and making the LH Bank weak . This manifested itself in an uneven ( for a Jag V12 you would hardly notice it, it would be normal on most V12s of the period) and a popping or gulping under acceleration. I am just about to go for a test drive so will report back . It may well be to do with the choke, to be honest, I didnt really even think about it because I have known for about 40 plus years that the Carburettor V12s are vunerable there and elsewhere to air leaks. Hopefully I will have a nice little run out to the pub in a minute!

[andrewh]

And back to perfection. Running like a little dream. Back in the day, when this car was new there was a very very good local Jaguar chap called Dave Griffiths. It was him who told me where to look when they don't run as well as they should. I suppose I shouldn't tempt providence but when these are set up correctly they are hugely stable and reliable. It always impresses me that Jaguar produced a V12 which by and large was extremely reliable against our Italian friends who built V12s that needed tuning every couple of weeks. And Jaguar were using the prince of darkness electrics as well!
Anyway, made it to the Pub , just a small exhaust leak to correct and then all done. May use it for Goodwood this year I think, as I get older its just the ticket

[Series1 Stu]

I love that car!!!
My favourite XJ in my favourite colour. And I still need a V12 in my life.

Regards

[andrewh]

Thanks Stuart, and a Shropshire car too. Supplied new to Frank Galliers Limited Shrewsbury, by Kennings. A wonderful traditional showroom at the bottom of Wyle Cop. I used to peer into the showroom every time I went to town.
http://search.shropshirehistory.org.uk/ ... wcookies=1

[baganz.sven@web.de]

Just one short comment.
The pipes are listed in the SNG catalogue in the section carburettor mountings (at least for my EV12)

Which material did you use?

Rubber or clear plastic hoses?

Sven

[andrewh]

I found some black hose from another car which I hope is fuel resistant but it has done the job for now. SNG did not have the rubber available , or at least they told me they didnt.

[Series1 Stu]

Do you know what bore and length you need? I bought a couple of metres to do the vacuum reservoir on my 3.8. I might have a bit left over that you can have for the cost of the postage.

I'll have to check when I get home at the weekend.

Regards

[andrewh]

I will check again what I measured it up to be. I think it was about 3mm ID and about 6 mm external but I may be incorrect. There is not a lot of room down there for any pipe that is too big OD. thanks for the offer, I will let you know