does anybody run them on their XJS? certainly no one on this forum.

anyone have any experience with these carbs?

ive been looking into these for a while but just cant foot the $4500+ price tag. someone on another thread said to just pick them up used, but how likely is it that i can find the 40 idf off of different cars with the same size jets and idle needles etc? or is this easy to rememdy?

ive been finding them on ebay for about $150 each.

found this manifold set that isnt very pretty for about $1500. Rob Beere-Induction

now i found this manifold set for MUCH cheaper and its MUCH prettier. ~$800
but i cant for the life of my find the HE linkage kit that they supposedly sell and even supply the part number for.
Webcon UK Ltd - 5.3 V12 6 x Weber IDF


a good running Jag with a weber setup is the kind of thing that i would keep for ever. lol

 

M90
I am sorry to say that I believe putting carbs on a roadgoing HE V12 is an utter waste of money. It will not run well and will drink fuel.

Greg

 

the alternative being 2 months of my life wasted for a car that doesnt run well and drinks fuel.


so the question is basically "are all 40's created equal?"

 

You'll find that your car will be "over carbed".
Let me use an example; I once had an Alfa spider with the Spica fuel injection(mechanical, sweet set-up when properly tuned). Like most young guys I wanted more power so i installed a pair of high lift cams and 45mm Weber DCOEs. At 4500 rpm and above the engine screamed - felt like it wanted to come right out of the car. Below 4500 rpm it was undriveable. I went back to the Spica with modest cams...

 

but im running the stock cam.

 

You'll find you'll be sucking too much fuel and air for the vast majority of your driving habits. Work out the problems you're currently having and then tune to get the best performance and efficiency for your driving style. It's really the best thing to do, IMHO.

 

anywho, are all 40's created equal?

 

NO, there are many different configurations of Weber carbs they might say 44 IDF but the jets can be different and there were at least 2 different float arrangements. This would be an expensive exercise and what happens if it does not fix your problems?

If you do decide to go carbs I would use what Jag fitted to the V12 quad Strombergs - these are also variable venturi won't give you as much outright power but will have better drive-ability.

Personally I would get the EFI working - there is a reason ALL new cars use EFI over carbs.

BTW the 16CU ECU you have is this from a Lucas car or a Marelli car? because a Marelli 16CU does not work properly in a Lucas car..... So I have been told. Because the Marelli and the Lucas 16CU units communicate with each other to adjust fuel and ignition.

 

Lucas.

i found a set of XKE manifolds but i couldnt find strombergs. i found Mikuni's, but after talking to some harley guys, theyre pretty difficult to sync up.


and i dont think 44 IDF's are the ones you need for the downdraft setup.

i have many threads dedicated to fixing the EFI system. This thread is for carburetors.
if you have some input as to how you would fix the EFI, then feel free to post it in one of those threads.

 

what if the EFI system is fine and ive been wasting my time from the start? sounds like i should just do nothing.

 

LOOK I OFFERED TO HELP IF YOU DON"T WANT IT FINE.

You have so many threads I have lost track. I do not read all of them. You need to learn proper diagnostic methodology and STOP jumping all over the place or you will never fix it.

 

How much horsepower are you willing to lose? A well tuned set of Weber’s in a XJS will cost you 30-40 horsepower over the stock fuel injection.
while they sure look good the hood is too close to the engine for the proper length air horn to be used.
That will cost you some power, maybe 20-30 plus Weber’s need to be constantly tuned or run really rich to not be too lean that it burns valves and holes in pistons. That will cost you more power.

Have you got a barometer? Or better yet air density meter? Then look at it through the day. Every time it changes you need to change jets, air correction meters idle jets etc etc etc. to stay in tune.
fuel injection does that automatically. So did the old SU. Not the Weber.

 

Mguar,

That's dedication! At the risk of disrupting the discussion, how did you stumble across a thread from 8 years ago?

Paul

 

Quite so