Finally got into the slow revving issue on this car. Worked out the secondary plug wire issue and the mini-arcing on the seats on the primary posts of the coil. Just a clean up and proper seating of newer plug wires.

Pulled the vacuum advance on the mighty OPUS distributor and it was reading 12 BTDC. I am thinking, that's where I might have tweaked it to for giving it bit more zip when it spools up. Owner's manual says 10 BTDC.

Put the vacuum hose back on and it reads 2 degrees BTDC at idle.

What the hell is going on? There is no retard function from what I can see.

Car runs better with hose off than on and the damned thing is a cream puff - just as old as Moses.

If I had to get this thing fixed fast I would have hung myself already.

Below is a pic of the crankshaft pulley to show that I at least know where to point the timing light. :-)

Is the advance vacuum ported? The hose is sucking at idle. Should it be?

Edit: Yes I know the alt belt is screwed up on the pulley. Just bought another today. Another happy surprise.

 

I have zero experience on the older V12s but I know some of the 70s vintage Jags DID have a vacuum retard (as oppose to vacuum advance) system so some weirdness might be expected. I really don't know the particulars, sorry.

Someone who knows something will come along


Cheers
DD

 

Yep, PreHE in USA and our market got vac retard.

However some have been altered to vac advance with a capsule change, and replumb to a "normal" method. One of them was ours.

If the vac hose attaches in the end of the capsule, opposite the rod, it is a vac advance unit. If the vac hose attaches on the rod side of the capsule it is a vac retard unit.

We also got some model years that had advance/retard in the one capsule.

The parts drawing here is showing a vac advance unit, as the hose goes in the end opposite the rod.



I cannot find a retard unit at the moment.

 

Thank you, Grant.

Yes, mine has the vacuum retard. Ahhhh, that is a good feeling that I MAY not have to pull that beast completely out.

Still sluggish on revving, and I need to check total advance, but at least I'm not losing my mind.

My 81 911 has both the vacuum and retard ports on the capsule for the US version cars.

May I plug the retard hose without ill effect? I suspect it's for US emission requirements and not an operational requirement.

 

Spoke a wee bit too soon.

Check this passage below regarding centrifugal advance from Kirby Palm's book "Experience in a Book"

Although, the book is for XJS' this has to be applicable to the XJ as well.

He is adamant about this one. "Folks, this is probably the single most important thing in this book" he says.

 

good info Grant, i just completed a distributor overhaul (modified)

cleaned and polished the shaft, oiled well.
changed the advance curve, to suit my needs, change weight by grinding some metal off(very little tho), used lighter springs, for quicker advance curve.

and then modified my vacuum capsul, using a GM adjustable,adapted to the jag capsul base.

all cleaned up,and use the Crane optical trigger pickup for coil and ECU-EMS.

new plugs IRIDIUM, new 9mm wires.

my old fashioned way of tuning, is advance timing until engine kicks back on start up, and retard about 2-4*,or until engine starts quickly, with my preferred curve, no vac, my light says 28* initial, 850rpm, no advance till 1200, all in at 2500-2800rpm,42*.

with vac applied, no advance till around 8" then goes smoothly to 52-54*,total.

vac directly into manifold, NO ported stuff, and absolutely no retard.

runs cool in 100+F temps in Texas, 180-185*,digital gage, cruising.

over all performance is outstanding, all things relative, premium fuel .

no pings or such, a lot of work but my engine seems to like it.

 

and my engine is a pre-he, 9.2-1 compression.

not sure if the HE would tolerate that kind of ignition setup, jag at that point was doing anything that would get better MPG, performance was secondary!

 

Bob,

That is MORE specific to the HE set up.

I have never seen a PreHE distributor seized, although I suppose anything is possible. The main difference is that the HE has that cap venting system, where one hose was in the "serious draft" of the AAV inlet hose, and I believe it allowed some engine fumes (oil saturated) to be sucked into the distributor, thus gumming up (or at least assisting) the mechanical advance bits. The PreHE has no venting system, so cruddy engine fumes simply do not get into the distributor. That is MY opinion after many years of messing with this beast.

Setting the PreHE timing is really a hit and miss at the age of them now, and the Opus is battling to keep up with "modern fuels" and all sorts of items like that.

Ours was vac advance (as I said) and was with a HE vac unit, and then I ported it from the "atmosphere" port on the under side of the RH throttle body. The Opus was replaced with a Crane XR700, and a Bosch MEC cube coil.

I set it a 10deg before, static, and then timed the fine bit by "drive timing" over a few days. The PreHE is waaaaaay more forgiving to advanced timing than the HE will ever be, but I also "drive time" the HE when needed.

Mal-adjusted fuel pressure on the PreHE is critical to performance, and setting those 2 FPR's to suit the engines requirements (NOT what the book states), is quite time consuming, and frustrating at times. One of ours was sweet at 29psi, and the other was sweet at 31psi, so it does really get to a "feel" thing with these engines.

I also fitted the 71mm throttle discs to all my V12's, and that really made a difference.

 

Grant,

You are right. It is not seized. Total advance is something close to 40 degrees. The numbers run out so I can't be precise.

I am thinking the slow throttle response may be related to the vacuum retard to a degree There must be some lag time from pushing the gas pedal to when the manifold vacuum is reduced enough to impact timing given the retard function.

The owner said it was peppier when he bought it in the late 80's so that is the only reference I have relative to what it was.

Other things I have considered.

1. The pivot bushings on the twin throttle linkage are GONE and the bar leading into the throttle has to twist around until it hits metal before moving the throttle. See picture.

2. The gas is really old. Many years.

Other symptoms. Car stinks rich pretty much all the time. Less stinkier after warm up.

I have done no studying of the injection system operation. I tried one pressure test looking for air leaks (soap in a bottle) but I am not certain of the common leak areas. All injectors fire and car idles / runs smoothly.

Any thoughts would be appreciated. Just a nudge in any possible direction and I will research.

Is the Haynes manual worth the $30?

 

OK, those pivot bushes are CRITICAL, I say again, CRITICAL.

An old VW Beetle of aircooled vintage will have more grunt than a V12 with those missing.

Fresh fuel is mandatory, and will solve many, many issues.

I have attached a "word paper" i wrote many years ago about setting the throttle rods on a HE. Same procedure as the PreHE, but forget #3 mainly, as you have a throttle switch and that is a fiddly thing to reset correctly, so messing with that is not for the feint hearted. The PreHE does not have issues with that capstan shaft seizing, so really just ignore the #3 paragraph.

Any more info you want, ask, i have heaps.

The Haynes is not the favourite, but I have one and it does aid for some things, and confuse for some others, but it is also better than nothing in my opinion.

Good old common sense works well mostly. It is only an internal combustion engine after all.

SETTING THE THROTTLE CAPSTAN AND RODS GRANT.doc

 

Outstanding.

Ordered bushings from Johns cars Monday.

To add insult to injury, one bushing is totally gone and one is partially present allowing the pivots to move separately from each other. One twists a lot and the other not so much.

Will check with my pal on gas. I think he may have splashed some gas in there for the two hour drive from his place to mine but I am not sure how much and/or which tank. They are both over half so I will siphon out and dump excess into my daily driver across time.

There are some non oxy fuel stations in this area. May go get a jug of that for the short term.

Thanks again. Will report back after going through the linkage set up.

 

I have the bushings......Not installed yet, but I got them.

The car has started backfiring under any load condition once close to warm. This started after I worked on the transmission mounts and changed out the fluid.

I overfilled the trans AND drove it three miles maybe. Sucked some out with a mightyvac and hose but it's still at least a quart over.

I am letting it sit for a couple of days to drain the converter (assuming this matters) before finishing the fluid extraction job.

Can this be related? Overfill and backfiring? I have read some posts where folks have mentioned to check trans fluid in threads related to engine function issues.

Have I caused damage?

 

NO, NO, and NO.

The old BW12 cares not for a tad more fluid, not a fussy thing at all. Ours leaked a LOT, and I simply stopped adding fluid, and eventually it stopped leaking, still went forward in D, and backwards in R, so care factor -100.

The backfiring may be many things, but out of sync throttle discs will reek HAVOC. Fit them suckers, and set up the rods etc as specified, and then lets start all over again if needed.

 

:-)

I'll shut up till I do.

 

NAH, just drink more, like I do.

Surprising how clear things become HAHA.

 

I put the new bushings in and have only had about nine American wimp beers and I think I see the light. That's at least two pints of real UK beer, right?

Car spins like a scalded dog without issue when the fuel tank button is "out" but does the backfiring and such when pushed in.

It did not do this before the bushings were installed. Meaning it ran like crap off of either tank. In fact, I dislodged the remaining carcasses of the old bushings about the same time I did the trans mount refresh. I bet, like you say, the trans fluid is far far away from the issue and I just got my "fixes" tangled.

I believe I gots me a fuel delivery problem, which is awesome relative to something wrong in the engine bay.

Gracias to you. Now I need to follow the procedure, supplemented with Kirby's write-up to dial it in. Also found some AJ6 stuff to help.

You ain't heard the last of me..............

 

Nice color of fuel from the fuel filter "in" side. Jeez, how about that sediment. Again, still happy that the tanks are crudded up vs OPUS being wacked out.

Watch this space...........

 

Bugga.

That looks like a home brew gone wrong.

I would not drink it, neither should the car.

I agree on the fuel versus Opus, at least you can see issues with the fuel, the Opus falls in that "smoke and mirrors" area.

Eletrical theory as per Joseph Lucas.doc

This clears things a tad more.

 

Bob:

You are probably looking in the wrong place for your "beer". The standard brands just don't get it. Now, some smaller breweries have it. I just had some Shocktop Belgian white. Very nice. And, even Trader Joe has a house labeled dunkel brau. quite good.

I didn't know what real beer was til I served in Germany in 52-55. Yum, yum, so much fine brew and so little time.

As to timing, I have never had the 'pleasure" of monkeying with a Jaguar V12. I have monkeyed with spark retard systems. Not all bad. The flat head fords used an unusual distributor designed by Mallory. Dual points, centrifugal advance and adjustable vacumn retard.

My method has been what I and others call "power timing", I start with a static setting of about 10 degrees BTDC. Drive and bump up a couple of degrees at a time til one gets a bit of a ping under load. I it is light, keep it. or, back down just enough to eliminate the ping. if one keeps it, gotta drive the car in such a way as to avoid sustained ping. Not good for cars driven by the unsophisticated.

Ignition in top nick has always been my mantra. If not, diagnosing other faults is nigh on to impossible.

I noted the adjustable vcumn can in a magazine the other day and wondered as to adoption to other critters. But, as my two cars do not have vacuum cans, only of academic interest.

The emission guided alterations seem completely misguided to me. How can a poorly running engine be cleaner than a well running engine???

 

pic of my adjustable vac unit.

you put a small allen wrench into the vac hose nipple, and turn a set screw in or out that puts more or less tension on the spring,.

i had to adapt it to the jag base, with rings to clamp it together.