'76 XJ6C Federal Emissions Transplant

I have recently acquired a '76 XJ6C #2J51560. She is originally a Federal car, but has had the Stromberg carbs and the EGR emission system removed. In their place are shiny HS8 SU’s. To return her to the road legally I will need to pass a California Smog Check. The Tailpipe test has certain allowed levels of the various gases - HC, NOx, CO. Much more difficult on this car - the Visual Inspection requires the original emissions equipment to be there, and working! :worried: :worried: :worried:
I’ve rescued several cars over the years and know my way around an old Jag with SU’s, but Strombergs and the EGR system are new to me. Please enjoy the weekly updates and guide/support my project of getting this beautiful car back to Federal condition, through CA Smog, and participating in the annual UBSCC Car Show on May 19th! Attend if you can, it’s a great all-British car show here in Northern California.
2024 UBSCC Car Show

Note the SU HS8’s, not Strombergs. No Air Pump, EGR/Gulp/Check valves, or air injection piping. The 6 threaded holes in the cylinder head for this have plugs in them. Empty holes for the Air Pump mounting brackets/tensioner. Empty slot on cooling fan pulley.

Next to the crusty, old-gas-stinking eBay '76 Strombergs that just arrived, we see there are just over 8 weeks left to the show. I see three Phases: Source Parts; Clean/Fix/Install Parts; Tune-Up. Once we apply for CA license and registration, we get a 30-day Temp Operating Permit so we can drive until Smog Check is done. We might delay applying to DMV until 4/19, so we can drive to 5/19 show legally even if not smog-ready.

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In this Source Parts phase, I need to thank the forum for putting me in touch with David Boger at EverdayXJ.com! Incredible support of Jag’s with lots of scarce used parts, and he had a 4.2L Carb’ed Federal donor engine! In transit from David is a “'76 Emissions Kit” he has pulled from this donor engine. I can’t thank David enough!

Items circled in red I am not sure where to connect right now, but I have Jag Parts Manual and ROM on the way. Pull up a chair and join me for a few weeks - here in Week 0, all the parts we need have been sourced and are in transit! :+1:
Key activities are to drain cooling system and start SU & manifold removal; start cleaning the Strombergs, and wait for manuals and all the rest of the parts. We got this!

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Pains me that you have to do this!!!

A couple of quick notes -

Your donor carbs have manual chokes, but your donor emissions kit, is coming plumbed for water chokes. Before you get too knee deep, make sure you can use and fit the manual chokes. The water chokes are absolute garbage, are nearly impossible to find in serviceable condition, and will make an otherwise perfectly setup motor, fail emissions horribly.

EDIT: Moss is selling new water chokes if you get stuck.

Manual chokes will mitigate this issue.

Second, it’s no surprise that I detest every facet of CARB, but have you spoken to the referee about not replacing the carbs (would they even know the difference at this point) and simply re-attaching the remaining bits (cat, egr, air pump, etc.)?

Be mindful that your cat will need to be CARB approved, and it needs to be in the exact location of the original (in the downpipe) not from a legality standpoint but rather to make sure it lights off to burn up and scrub the NoX, which is where you are going to struggle most with passing.

I own a British shop in Colorado (we are CARB here now), and am at the emissions station a few times a month, lots of XJ windscreen time getting these cars through. The benefit we have here, over CA is no visual inspections (what’s the point then, right?), but I set the cars up 100% legally regardless.

Lastly, due to internal engine conditions, some of which aren’t negative at any level, some cars just won’t pass (not to throw a negative spin on your efforts), and it forces folks to register their cars out of state in order to enjoy the few miles they put on them yearly.

It’s a very, very poorly designed system that is run by folks with little to no knowledge of early carbureted or injection setups.

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Forgot to add - make sure you completely tear down and rebuild the Strombergs carbs, and don’t forget the throttle shaft seals. Without the same, you’ll get a vacuum leak that will make setting the needles and idle impossible. You also need the Stromberg mixture tool (easily available), and if you are getting over your skis at any point, don’t be afraid of sending the carbs off to a guru (like Joe Curto in NYC) to have rebuilt professionally and have arrive in more or less bolt on, drive home condition.

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I have the complete Federal setup I removed from my 1975 XJC (no need for SMOG in California). Let me know if you need it.

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Yes, very interested. I sent a message through your profile, if I did it correctly.

I really wonder if there still is a technician certified with the state of California who really knows what to look for and how to test these old smog devices. If the equipment appears to be present then perhaps a visual inspection isn’t so hard to pass, but testing for functionality is likely a lost art and at best a very time-consuming task for a tech. Aside from sticking the probe in the tailpipe, nowadays it’s just the simple task of plugging the car into the computer and reading the codes if I’m not mistaken. Being in my late 50’s and having learned about them in my 20’s, I’m not confident that the newest generation of smog techs is equally schooled in these crude artifacts. I myself will have to face the state of California if I ever get my fuel-injected 1979 XJ12 on the road again.


I left California decades ago. But, back in the day, the “smog technicians” didn’t test the functionality of all the emissions equipment. They did a visual inspection to make sure al of it was in place.

Then came the actual tailpipe test.

If all the equipment was there and the car passed the tailpipe test then you’re good to go for at least a couple more years.

If all the equipment was there and the car failed the tailpipe test then the car needed to be repaired so it would pass the tailpipe test. There were cost limits, various possibilities for waivers, etc.

Missing equipment needed to be reinstalled regardless of expense, however.

My recollection is that CARB has accurate records of what equipment the cars were built with so the tech know what to look for. However, in-depth experience of how it all actually functioned was not required for the purposes of inspection.

But, that was a long time ago. “BAR 90” was still the protocol. Not sure how things might’ve changed.


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My mistake in my wording. As Doug says, they visually check the devices are present, but do not test each device individually to function. If the parts are visually there and the car passes the actual tailpipe emissions measurement test, its a PASS.

Not at all. My comment was more rhetorical than anything. I was aware that the test was only visual and not functional. That being said, I do remember that for my XJ12 only certain replacement catalytic converters were certified for use in California and had the appropriate markings. I think it is likely, however, that once a technician sees a cat where it is expected that a pass will be given and will go on to the tailpipe test. My partner’s 1983 Renault 5 aka LeCar passed with all its emission equipment visually intact but not tested and and a new cat installed.

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It started with CO testing, Cedric - then progressed with HC and Nox. And states adopted different regimes - it’s not immaterial if the engine is hot or cold, at cruising speeds or whatever, under load or accelerating - no car with ‘our’ technology could possibly pass them all…:slight_smile:

xj6 85 Sov Europe (UK/NZ)

Week 1 '76 XJ6C Federal Transplant update: On Track!
Goal #1: Attend 5/19 UBSCC Car Show - High Confidence, Low Risk :+1: :+1: :+1:
Goal #2: Pass CA Smog by 5/19: Low-Med Confidence, Med-High Risk. (A bit stickier wicket than goal #1…) :roll_eyes: :grimacing: :grimacing:

Phase Summary:
Parts Sourcing: Donor engine components due in 3 days. Air filter baseplate and carb spacers on order. Parts Manual still stuck in IA USPS “Acceptance Pending”. Fuel Evap system is still on the car!
Parts Cleaning/Fix/Install: eBay Strombergs’ rebuild is underway.
Tune Up: Compression test, Manifold vacuum test, and valve lash measurements finally reveal why she runs so poorly! Rookie mistake has been found!

Key Week 1 Activities: Complete Stromberg rebuilds. Start cleaning donor parts. Start valve clearance adjustments.

We got this! Details/pix below…

Parts Sourcing Detail: Gotta work with the water-chokes. Both the eBay and Donor Strombergs are water-chokes. Air filter baseplate had been drilled/openings enlarged to fit the SU’s, damaging the float chamber crossover duct in the plate. Dave at Everyday XJ has a plate, and the carb to plate spacers.

Parts Clean/Fix/Install Detail: 1st eBay Stromberg rebuild underway. Joe Curto kits, upgraded floats, Stromberg mixture adjusting tool in hand. Carb had a dime as the cap on top of the water choke, and the Throttle Valve Bypass has been blanked off with a home-made gasket. As advised, the throttle shaft bushes/seals will be replaced.

Tune-Up Detail: She runs extremely poorly: sputtering, missing, backfiring, won’t idle, etc. Before removing the SU’s, we need a baseline on the motor.
Compression Test shows front three cylinders weak 110-115psi, rear three better 120-125psi. Pouring 5ml of engine oil into weak 3 cylinders improved compression: rings are leaking, not the valves. New plugs with 10 minutes run time very sooty on rear 3, very sooty and some ash deposits on the ground electrode on front three.
Borescope shows quite a bit of (now oily) carbon deposit on #6 piston, and perhaps not-factory hone marks on the cylinder walls. Does she have 106K miles, or 206K miles?

Manifold Vacuum Test showed very low vacuum, with a very bouncy needle. When these intake valves open, they are venting/pressurizing this manifold, not only drawing a vacuum! Wish I could post the video… Needle bouncing violently between -15" vacuum and +4" pressure! Sure enough, intake cam timing is wrong - it is too early. (Tip: Verify pointer’s TDC accuracy by ensuring pistons 2-5 are all exactly mid-stroke. A suitable length dowel will protrude out of each spark plug opening by exactly the same amount at TDC.)

Exhaust cam timing was perfect. It is very likely that the PO set the intake cam for TDC, THEN tightened the upper chain tensioner (which advances the intake cam a bit) and didn’t bother to check the cam position again. Always set the cam with the upper chain still appropriately tight, spin the engine a couple times, and check the cam timing again. And don’t drop the cam bolts/lock plates down into the engine!

Valve Clearance measurement revealed all the Intakes are way too tight (so also opening earlier) and only 1 Exhaust is tight, 5 are in-spec.

Distributor drive gear position is correct for TDC. Distributor mech advance and vac diaphram are good.

After correcting the Intake cam timing, she ran quite a bit better, with a steadier vacuum -15" Hg or better. Still not running very well, though. The rear SU has a clog between float bowl and jet, so she is essentially running only on an overly-rich front SU. I’m not investing valuable time in fixing the SU’s - I’m going to start the valve adjustment, and press on with the Federal parts!
Enough for today - Week 2 update will be next week. Thanks, team!

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God running not to be expected without the carbs synchronized, Bob - the compression is within specs for differences. Should cause no running
problems - but difference in bore wear, the front and rear three, is a bit odd, but is what it is…
Don’t expect any improvement in running when valve clearances are rectified - clearances are essential for other reasons. With carbs sorted; running will improve…:slight_smile:

You have not mentioned ignition timing - but I trust you have verified that TDC pointer is correct with #1 or #6 at TDC…

xj6 85 Sov Europe (UK/NZ)

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Compression is fine and chains rarely line up perfectly. As long as it’s not out by more than a notch with it is not really concerning, less overlap means better idle and more means more top end power… just adjust it. Wear also changes timing!

Drive a bit after fixing it sowell and it‘ll be a good car!

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Week 2 Update: On track. 6 weeks until UBSCC 5/19 show… passing smog? Uh…

Help Needed: EGR Valve Options? The major suppliers don’t offer a new Series 2 EGR valve. I see “rebuilt” ones on eBay (same as 75-76 TR6) in the $240 range. Is there a new aftermarket valve that can be easily adapted? How do we address a failed diaphragm on an original EGR valve? Thanks!

Donor Parts arrived and are cleaning up nicely. Intake manifold painted black (low gloss) along with the vacuum and water pipes. (Whoops, pipes probably should stay bare metal to avoid a deduction at a JCNA event. Also, the hose clamps aren’t correct either, I believe.) Ready to bolt onto the car!

With Stromberg rebuild kits, Bypass Valve Diaphragm kits, and the manuals, rebuilding the carbs was straightforward. That water choke is indeed a special little mechanism, isn’t it? I see why they’re $500 new at Moss! A 6-32 panhead screw 2" long and a 5/8" socket work well to press out the jet.

I’ll be lucky if the water chokes work more than a couple months before one sticks open. I see Manual Choke Conversion kits for these carbs - but only for one carb. Anyone found a conversion kit for this dual Stromberg setup? Note that one can force the choke closed through the open vent with an appropriate tool. Once installed, only the fast idle plunger’s position indicates if the choke is open, closed, or somewhere in-between. What a poor design!

Key Week 3 Activities:

  1. Transplant the manifold and Strombergs onto the car, and get her running nicely for a baseline. Then I can add the air pump and EGR emissions equipment piecemeal.
  2. Visit Eric and get his removed parts… one can’t have too many Jag spares.
  3. Start the valve adjustment and get needed shims on order.

See you all next week, let us see how well she runs on the Strombergs!