Hi all- I'm getting my freshly rebuilt 4.2 ready to go back into my XJ6C, and have a rebuilt set of 420G Triple SU carbs ready to go on.... I just noticed that the original thermostat housing/ header tank that mounts on the forward end of the intake manifold won't work with the older triple carb intake. It physically fits, but does not cover all of the area that has water flow. Is there a part I should use here instead of the original Series 2 part? Does the 420 have a similar thermostat housing with fill cap/ etc?

Has anyone done this that can elaborate?

Thanks!

 

• It has been over 15 years since i did that mod on my S1. I believe that i used the S1 thermostat housing (Stromberg carbs) at front of the 420G intake. I recall it being too tall with the fill cap and i replaced the cap with a shallow threaded plug (pipe thread). The two small hose connections got added to the side of the housing where i tapped in a couple of threaded hose barbs.

 

OK, so I think I have this part figured out. Now on to the throttle linkage and other hookups. Can someone tell me what the second nipple on the rear end of the manifold is for? It seems to be a vacuum source pulling from just behind the carbs, also where the cold start fuel enrichment goes. I pulled the hose off of the end and it smelled very fuelly. Heater hose goes to the nipple next to this.

Then- I have to finalize the throttle linkage -- any advice? Looks like the bracket that came with my manifold may work with the XJ throttle cable, but then there is no provision for kick-down trans cable. May be trial and error getting throttle travel right etc... I have struggled to find anything other than a few pictures of similar setups online, but nothing describes the linkage very well.

 

I've just done this to the 72 Series 1 I've built. The nipple on the back of the manifold you're talking about is a vacuum source that you can use for the heat/AC or cap off if you are not ready to hook it up. Cold start enrichment from a 420G should be a starting carb connected to the manifold with metal pipes. Not sure what hose you're referring to smelling fuelly.

I used my original S1 throttle setup with some simple modification to mate with the 420G setup. I could show you that but it is different than S2 - you might consider switching to S1 because it might be easier since it is basically self contained. You will probably have an issue with the diagonal brace interfering with the middle carb. If you're using the original 420G metal carb distance pieces and o-rings that makes it even worse. There are 2 options to fix it, machine the mating face of the manifold so that it slopes down a little or just use E-type fiber distance pieces and an extra gasket on each. This gives just enough room to clear while still allowing the top carb linkage to not impact the manifold.

For Cooling, everything past the main manifold is S3 XJ6. I made an 1/8" thick aluminum plate to block off the original, 420G bypass and I'm using S3 thermostat housing and water outlet. This does away with the problem of the S1 header tank interfering with the hood. To do this you need a S3 waterpump as well as the expansion tank (you can see it in the pic). I have a custom aluminum radiator but you could use standard S3.

 

Great work!! Looks awesome.

Jeff H.

 

Does look just beautiful! S3 washer tank would add a little more class, otherwise perfect!

 

Hi Bob!

I would've used the S3 washer fluid tank but I had that perfect, NOS Series 1 tank lyin' around doing nothing

 

Great job. Congrats!
Where did you source the Alum Rad and the Electric cooling fan? I'm considering an upgrade for my SIII and really like the clean look you have achieved.

Ian

 

Thanks Mike- this is helpful. I was doing the same thing with a 1/8" aluminum block-off plate for the water bypass, but planning to use my original S2 header setup with fill cap. On first inspection, it looked like it will be in the same location it always was, but you're saying it will hit the hood? Is it further forward with the 420 intake? I have a throttle cable bracket for the 420, as well as my original S2 bracket. Will take some fiddling to get it to connect to the 420 intake, I was going to try to use the one from the 420 as it looks like my original throttle cable will fit. Was it difficult to get the linkage hooked up to the S1 bracket and opening and closing the throttles fully? Did you use phenolic carb spacers on all of the carbs, or just the middle one? In the photo, it looks like only the middle one sits closer to the manifold...

Looks like you have the original cold start enrichment set up from the 420? Does it work OK? Did you run a wire from the coil?

Are you still using the trans cooler? I don't see it... By the way, what transmission are you using? Do you notice a difference in performance with the carbs?

 

@iramphal Thanks Ian - The radiator is from a 97-2004 Mustang. As you can see,, they are the same setup as the Jag part. They even have pins at the top and bottom for locating them. You'd need to fabricate mounts for the bottom and a way to trap the ones in the top but the rads work really well and available off the shelf. Fan is a regular Spal 16" with a normal adjustable fan controller. I have 2 Series 1 XJ's that have these aluminum radiators and electric fans and they work great. I can give more details if you're interested.

 

@SableXJ6C Thanks! The original header tank that hangs off the manifold will most likely hit the hood - it can be done with modifications of the filler neck though. It will also probably wind up at an odd angle - rotated a little. You can offset that with the plate you're making. That's why I went S3. All you have to do is make a plate to block off the 420G bypass slot and get a S3 waterpump - cheaper and easier to get than S1 these days. If you use a S3 rad than all you need is the expansion tank. If you go Mustang rad, you also need to add a T in the lower water outlet to attach to the S3 tank.

I actually bought a S2 throttle shaft assembly just for parts and to see if I could get it to hook up to the carbs' linkage. I found the S1 version MUCH easier to modify and get it to work. It only required a new arm welded on. a pedestal for the secondary shaft and some spacers and other off the shelf parts: heim joints, bushings, spacers. I did use a piece of the S2 assembly however but only as a shaft. Everything worked out really well.

The carb spacers - or distance pieces as they call it on some supplier sites - are the thinnest versions from an E-type with Triple SU's, they're on all carbs. I had to use 3 gaskets per carb instead of 2 to give me that tiny bit extra space so the upper linkage didn't impact the screw that holds on one of the enrichment tubes. (thanks @Robert Wilkinson!)

Mine is a manual overdrive transmission now (was BW12) but the radiator does have provisions for auto trans cooling lines

Original starting carb is functional. I used the choke indicator light circuit to power it so you basically just pull the choke lever to start as usual. You can just use the otter switch in the manifold to activate it but I wanted to be able to have control over it. It works fine to start the car but I find that it seems too rich even at full-lean adjustment. Thinking about making a leaner jet for it but it's not high on the priorities list.

I should also mention that the Mk10/420G carb bells have taller 'necks' than what you see in the picture - these were modified to E-type height by Joe Curto. If you don't modify at least the front one in this way, it will probably (almost certainly) hit the hood. After doing this you'll need shorter, E-type dampers or the carb pistons won't be able to go all the way up at WOT.

It's hard to quantify any performance differences because this car is very different from original. I will say that I've gotten my 73 with regular ol' Strombergs to run amazingly well (and it's pretty quick as well). Strombergs have an undeserved bad rap IMO. Their biggest problem (besides water chokes - those deserve a special place in hell) is poor maintenance. I'm sure there will be some small performance difference with the triple SU's but the coolness factor is definitely off-the-charts

 

Thanks a bunch. I'll try to source the parts.

 

Looks great! I have those same air cleaners on my triple SU's did you have to tweak the one nearest to sidewall to fit?
I used a Lokar throttle linkage.

 

Got any pictures of that throttle linkage setup? How did you mount it? Is it one of the 4 barrel setups?

 

I have the original MkX/420 throttle linkage but the mounting points for the actual cable were bodged up by Po so I used one these

Lokar Throttle Cable Bracket
Part Number: 625-TCB-40HS

and their cable to the accelerator pedal. I've used these on other vehicles (my IH Scout II for example) and they are well made and easy to set up and adjust.

Will take pictures when I'm next at car

 

Thanks @olivermarks !
My air cleaners fit without modification.

The only linkage parts I wound up buying were a Redline brand arm (for webers) and a couple of heim joints. The rest was Series 1 with a new arm, a spacer, a shaft and a bushing. I think I have a pic somewhere...

 

Here is the linkage I used. The Series 2 shaft connects to the 420G shaft in the same way as original. You don't have to use a S2 shaft, it's a standard 5/16 throttle shaft - but you should modify the end that rides in the 420G throttle shaft bushing so it is like original to eliminate any binding issue.

The pedestal that holds the Series 2 shaft has a brass bushing in it. Shaft is held in place - trapped - by the split collar and the gold arm - both off the shelf parts. 2 heim joints are a male and female threaded into each other.

Only mod to S1 linkage was cutting off the original arm and welding on an arm I made at a better angle. Arm is purposely the same size as the gold arm I used for the S2 shaft. I wanted to make sure there were zero issues with the amount of 'throw' there was in it and I wanted it long so there was a decent amount of leverage/torque to open all those spring loaded carb shafts. Works well.

 

Mike- Did you have to change the carb studs to fit the E type insulator spacers? It seems that the 420 studs have a shoulder that will not allow the carbs to pull up any tighter.

Confirmed today that yes, the header tank is on an odd angle, and the middle carb definitely will interfere with the K brace support. I'm still hopeful that I can make the header tank work as is and use my newly installed series 2 water pump... Looking good to use the 420 throttle linkage with the Series 2 cable, trial and error on lever arm size for travel, and I still have to rig something up for the kick down cable on the 700R4 transmission.

 

Yeah - sorry forgot to mention the studs. New E-type studs and then obviously you don't use the spring insulators and extra washers either. Just regular split lock washer and nut. In my pic of the linkage you can see I was trying to use the old stuff but had to change after I saw that the diagonal brace doesn't fit. With the E type distance piece plus 3 gaskets per carb you should clear the brace. The only issue could be the individual carb linkage might touch the manifold a tiny bit. I had to take a small file to some of the casting flash on the edges to give me just enough clearance. You'll see what I mean if you have the issue.

Header tank will work but you're gonna have to mess with it. Most of the conversions I've seen (through alot of googling) do it like that. @Robert Wilkinson is the only person besides me who I've seen use the S3 method, in fact it was my conversations with him about the conversion that made me realize it was a good way to go. I hadn't actually thought of it until then.

It's been a long time since I had a S2 but if the water pump has the later, smaller bypass inlet you could use that for the S3 header tank conversion if you had to. Also, if the bypass inlet is removable you could get the smaller S3 inlet if, in fact, the S2 has a huge inlet like the S1. The S1 pump is the problem because the bypass inlet is part of the casting (at least in all the one's I've see). I have heard of S1's having a removable bypass inlet however.

I wound up using my aluminum bypass blockoff plate, the S1 thermostat housing (same as S3 and probably S2) and then a S3 water outlet (which is where the bypass outlet is).

 

How did you remove the upper studs from the carbs? Cut them off?