XJ6 & XJ12 Series I, II & III 1968-1992

XJ6 converting fuel injection system to carburetors

 
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Old 03-01-2012, 09:15 PM
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Default XJ6 converting fuel injection system to carburetors

Hey guys I just decided to convert my XJ6 fuel injection system to carburetors

Could you guys give me advice on what carburetors I should use?

im looking to get better performance
 
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Old 03-02-2012, 02:56 AM
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You need to post in the XJ6 Series 1, 2 & 3 forum, where experts will no doubt be able to advise you. This will be quite a modification, as carburettors only receive a low pressure fuel supply, unlike EFI so you will need to use parts off a Series 1 or 2
 
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Old 03-02-2012, 08:58 AM
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+1 on fuel pump supply pressure.

In addition, you will need to also swap over the camshafts from a Series II engine and reset the valve clearances. Finding a donor engine may also prove difficult as all the manifold fittings and carburettor linkage are also different.

Unless you intend to race the vehicle, such a drastic modification is expensive and time consuming, which will also prevent it from passing any emissions tests that may be required where the vehicle is operated.

NBCat
 
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Old 03-02-2012, 01:50 PM
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I'm actually considering doing this as well at some point. There are several companies out there that sell E-type triple weber intake manifolds which is the route I would like to go. I did the same conversion with dual webers on an older fuel injected VW Rabbit with a 16v engine, it's not very difficult. The ignition system can stand by itself. The main issue will be whether or not the webers fit and what, if anything will need to be modified for them to fit. Fuel system part of it is fairly easy, just replace the central fuel pump with a low pressure electric pump and install an adjustable fuel pressure regulator with a return line on it in the engine bay. You can get the E-type weber kits for about $2200ish pre jeted with new carbs and manifold, the main obstacle is do they fit and what will it take to make it fit. The manifold by itself costs about $800-900 if you want to source your own used webers and tune/jet them yourself. Just thinking off the top of my head I would imagine the battery would be a likely candidate for relocation if you were to do it.


Triple Weber Carb Kit - Terrys Jaguar Parts

Airtex 110-E8251 - Airtex External Electric Fuel Pumps - Overview - SummitRacing.com

Mallory Ignition 4309 - Mallory Fuel Pressure Regulators - Overview - SummitRacing.com
 

Last edited by vwtechnician; 03-02-2012 at 01:55 PM.
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Old 03-02-2012, 04:11 PM
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How much additional performance do you think you can realistically get by doing this?
 
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Old 03-02-2012, 06:31 PM
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Originally Posted by amcdonal86 View Post
How much additional performance do you think you can realistically get by doing this?
I was told 35-60 horsepower increase
 
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Old 03-02-2012, 10:12 PM
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I'm not against using carbs, but just to make sure you are aware of all your options, have you thought about a stand alone fuel injection system such as Megasquirt, which you would have to put together, or there are others that are a little more complete such as this outfit: Simple Digital System EM-5.

You could also have the existing efi system modified: PERFORMANCE FOR THE JAGUAR XK 4.2 ENGINE. / AJ6 Engineering Scroll down and you'll see what kind of modifications/parts they offer and some hp figures.

Oh yeah, my understanding is that the heads of these XK engines responds very well to some good porting.

Good luck. I understand the desire for some more ponies to help these cars get up and go.

Eric
 
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Old 03-02-2012, 10:24 PM
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Standalone is certainly another option but I would prefer the carbs. The sound alone of the sidedraft webers would be worth it. Besides, the rest of the car's technology is from the 60s and earlier, might as well match the fuel system to it.

Ultimately what I'd like to do to mine is port out the head, dump the cat, put on triple webers and back it all up with a 5 speed manual and some bilstein shocks. Make it into a little bit more of a sports sedan, afterall much of it underpinnings come by way of the E type, it's not an incompetent chassis at all.

As far as power, it'll certainly give you a bump but who knows how much. If you were doing the triple webers one of the huge advantages is you now have a throttle opening for each individual cylinder which means you can get more air into the engine. More air = more power and the throttle response will be night and day. Ultimately though the cylinder head is where the real restriction lies. Paired with some porting in the head and a free flowing exhaust webers should be able to realistically approach 250 hp out of these engines.
 

Last edited by vwtechnician; 03-02-2012 at 10:27 PM.
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Old 03-03-2012, 12:43 PM
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The only power increase from carburetors, IMHO, would come at wide open throttle at higher RPM. If that's what everyone's is after, then carbs are the way to go.

I honestly can't see low-mid range power increasing by changing to carbs alone.

The biggest handicap in a Ser III in the 4000+ pound curb weight coupled with a 2.88 axle ratio (3.07 on very early Ser IIIs). High rpm power increases will not do anything to overcome the weight/gearing problem. Add all the horsepower you want but unless you're operating continuously in the 4000-5500 rpm range, you probably won't be all that happy with the end result.

Cheers
DD
 
 
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