Vacuum Pipes on series 3

Talk about the E-Type Series 3
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vee12eman
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#41 Re: Vacuum Pipes on series 3

Post by vee12eman » Fri Aug 03, 2018 9:50 pm

Hi Hilton,

If the distributor vacuum retard is fed from the inlet manifold, this is bad. The setup is designed to give retard at idle only and to do this, the vacuum used for control must only be present at idle. This is why a tapping is provided from just below the carb butterfly, on the left rear carburettor lower flange, as shown in Colin’s first photo on his previous post. Look closely at this because it seems likely there may be another uncapped tapping in that location. In simple terms, the vacuum sensed here is caused by the air passing through the Venturi formed by the carb butterfly to the throat of the carburettor. This is set up only to exist when the butterfly is (nearly) closed, a condition which exists only at idle. When the butterfly is moved (i.e. you open the throttle), the Venturi ceases to exist, the vacuum goes away and the retard unit has no influence until you idle once again.

I am not an expert in all things Jaguar, but I know that most V12 E-types (possibly all of them), were equipped with carbs which had this tapping on the LH rear unit. If it is open then another leak source is present and this will as previously stated, make it hard to balance the carbs and give uneven running.

As to the fact the car runs well with this incorrect connection, well it is highly likely the retard unit does not work. I have seen several and all of them have failed. They fail for various reasons; the diaphragms split (this happened to my brand new unit) which I actually repaired) and they also fail because the seal around the internal operating shaft wears out. In the latter case I have had some success in replacing the seal, but I have no idea of the longevity of this repair, since I only tried it for the first time recently on a friends car. I also found that even when they do operate, that when mechanical connection to the distributor is re-established, they can be too stiff and need just a hint of a bend to made to the operating shaft. The car will run pretty well without the vacuum retard unit operating, since in normal running, it has no influence. The first step most take to modify the system, is to blank off the supply, rendering it no-operational at all times.

While I realise you are actually trying to re-establish the intake temperature sensor operations, the whole vacuum system and oft associated leaks are a major source of problems with the V12E. Have you had any success in testing the sensors, or locating any for sale?

Regards,

Simon
Simon S-Y
Series III FHC

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lowact
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#42 Re: Vacuum Pipes on series 3

Post by lowact » Sat Aug 04, 2018 2:12 am

Simon, how long is the road in Kiribati? :bigrin:
Hilton, not trying to change yr ignition, only trying to help u find vacuum leaks.
U don't have gulp valve, so no leaks due to this, good.
U don' have vacuum assisted carb. bypass valves, good(ish), doesn't mean yr carb bypass valve diaphrams are intact, another story.
U have sorted out yr air inlet temp control, good.
U have capped the spigot under the LH carb that originally supplied the retard distributor? If so, good.

You might, as Simon explains, have a leaking distributor vacuum diaphram. To test, attach a tube to your retard distributor and suck on it. If you can suck continuously, it is not working and would be causing a vacuum leak.
Because u have retard distributor it doesn't matter (much), as long as you DO NOT connect it to manifold vacuum, Whatever the condition, do not connect retard distributor to manifold vacuum, if not connected under the LH carb, don't connect to anything, cap the manifold tapping that u were using, this is where u connect yr vacuum test gauge, essential and cheap tuning tool.
Regards,
ColinL
'72 OTS manual V12

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vee12eman
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#43 Re: Vacuum Pipes on series 3

Post by vee12eman » Sat Aug 04, 2018 3:50 am

Hilton,

Colin has raised a valid point regarding the bypass valve diaphragms, which are very likely torn or damaged by now. However, as he also said, that is another story. Most important thing is to find and cure leaks, then make the various vacuum driven units either functional or excluded, at least for now.

Regards,

Simon.
Last edited by vee12eman on Mon Aug 06, 2018 4:40 am, edited 1 time in total.
Simon S-Y
Series III FHC

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Holeshot
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#44 Re: Vacuum Pipes on series 3

Post by Holeshot » Sat Aug 04, 2018 5:30 am

Hi Simon/Colin.
Thanks for all your attention.
This is all very interesting.
Since reading the latest 3 posts I haven’t been able to look under the LH rear carb to check for the retard feed to the distributor (and check whether capped) but shall do so ASAP.

So, in summary, if my distributor has the original vacuum retard facility (with vacuum feed exiting towards the rear of the car) then this should under no circumstances be connected to any inlet manifold.....only to the under-carb tapping?
If the tapping that feeds to the vacuum retard isn’t to be used, what *should* be connected to it(if anything)?

The ignition system is a brand new SNGB upgrade with the standard vacuum retard.
However, I recently(mileage wise) had some cosmetic work done under the bonnet where much was dismantled. Beforehand it ran, like I said, pretty well, but since getting it back, a load of issues have cropped up.
Before speaking to you, I assumed that all things were put back where they were, but now consider that this may not be the case, and the tube to the vacuum retard could well have been put back in the wrong place.
I have been running the car recently where it runs smoothly with the new ignition so thought things were OK.
One thing that has been causing me concern and was going to look into it was that if I stick my foot to the floor to accelerate, it starts to feel like it’s not running in all 12 cylinders and loses power & response. Could this be anything to do with this vacuum?
Sorry for asking all these things as normally I’d just go out and experiment with the vacuum feeds and tell you the results but the car has the exhaust manifold off at the moment (another story!) so can’t do anything.

I’ll let you know my findings on the tapping below the carb.

Cheers, Hilton
Hilton - V12 2+2

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lowact
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#45 Re: Vacuum Pipes on series 3

Post by lowact » Sat Aug 04, 2018 7:38 am

Aha, u have a non std distributor! If the vacuum connection on the distributor is pointing towards the rear of the car you have a vacuum advance unit, not a vacuum retard unit. Note we are talking about the connection on the distributor vacuum unit, not the tapping on the manifold, the direction the manifold tapping points is irrelevant.

If u have a vacuum advance unit, the connection that you had, to the manifold, is correct. One of the features of the new SNGB distributors is they are designed to look like the original (retard) units. I.e. it might be an advance unit disguised as a retard unit. To be absolutely certain what u have, take off the distributor cap, so u can see inside while u suck on the vacuum line. If the mechanism moves clockwise it is an advance unit, connect to the manifold as u had it, cap the tapping under the LH carb.

Also, I'm imagining there would have been instructions with the new SNGB unit that should say exactly how the vacuum to yr new distributor should be connected?

Gross vacuum leak would cause the acceleration issue u describe. If this still occurs, i wouldn't say yr running smoothly?
Regards,
ColinL
'72 OTS manual V12

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Holeshot
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#46 Re: Vacuum Pipes on series 3

Post by Holeshot » Sat Aug 04, 2018 7:52 am

Just checked under the LH rear carb and the tapping has been blanked off.
So I should disconnect the vacuum feed the the distributor vacuum retard then, right?
Thanks,
Hilton.
Hilton - V12 2+2

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#47 Re: Vacuum Pipes on series 3

Post by Holeshot » Sat Aug 04, 2018 7:59 am

Sorry Colin.
Just posted that last reply before I read your last post. Be back in a mo. Cheers, Hilton
Hilton - V12 2+2

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42south
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#48 Re: Vacuum Pipes on series 3

Post by 42south » Sat Aug 04, 2018 9:34 am

Hilton
The Sng distributor has a vacuum retard unit as per the original set up. Just blank it off,and the port under the left hand rear carb.
You don’t need anything connected to the port under the carb.

Cheers
Mark
Mark Brown
1971 S3 Etype
Son: when I grow up, I want to be a pilot
Dad: You’ll have to choose.

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#49 Re: Vacuum Pipes on series 3

Post by Holeshot » Sat Aug 04, 2018 5:01 pm

Thanks Mark,
It was my understanding that the SNGB ignition was a direct replacement for the original ie. retard so left the vacuum pipes as they were. I shall remove the vacuum pipe that currently runs to the inlet manifold and blank everything off. Can’t think why it should have been connected to this in the first place.
Colin - maybe I’ve overstated things when I said it runs smoothly. I did a 150 mile round trip a few weekends ago where it ran beautifully apart from the one time it had that power loss - I’ll see if changing the vacuum set up cures things.
Simon - I forgot to mention about the temp sensor.
I pulled one out from the housing and it’s casing and tried to test it, but hot air with hair drier failed to make any difference in sucking resistance so presume it’s knackered. I found that oldstockspares in Devon have them in stock but am waiting to hear back from them. I’ll let you know how I get on. If they do actually have them then I’ll buy a pair.

Cheers, Hilton
Hilton - V12 2+2

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#50 Re: Vacuum Pipes on series 3

Post by lowact » Sat Aug 04, 2018 10:46 pm

Dirty fuel filter another likely cause.
Regards,
ColinL
'72 OTS manual V12

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#51 Re: Vacuum Pipes on series 3

Post by Holeshot » Sun Aug 05, 2018 3:23 pm

Good thinking Colin.
I stuck a new filter in a couple of weeks ago just in case.
Still got the random weird power loss.....
Once I’ve found a place that sells an exhaust manifold that actually fits properly, I’ll get the car running and test out all the above advice and see where I get.

Thanks again,
Hilton.
Hilton - V12 2+2

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vee12eman
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#52 Re: Vacuum Pipes on series 3

Post by vee12eman » Mon Aug 06, 2018 4:52 am

Hi Hilton,

Good luck with the temperature sensors, I definitely feel they had positive effects on my car, reducing warm up time, though I did not check scientifically.

I note you have other issues and components removed. When you come to rebuild, take time to ensure there are no air leaks. I used very small smears of silicon sealant on most air pipes, also using new pipes/tubes and clamps. I actually spent some evenings doing this and was rewarded with a much better running car.

All vacuum system components are designed to improve the car in some way, but many have questionable success in achieving this and if they go wrong can cause more troubles than their benefits ever gave. The general consensus appears to be that most, if not all, could safely be disconnected and blanked off with little or no negative effects and even some positive ones. I chose to make them work, for my sins!

Regards,

Simon.
Simon S-Y
Series III FHC

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#53 Re: Vacuum Pipes on series 3

Post by Holeshot » Tue Aug 07, 2018 2:53 pm

Hi Simon,

It's been so useful for me to hear everyone's advice. Just on this one small detail, I've learned such a lot about things that up to now have seemed like a 'black art'!

Perhaps for me, a little knowledge may be a dangerous thing, but I believe that now I can try things out with an understanding of what is right and wrong and what does what.

I'm all ready to reassemble the car once I've overcome a badly fitting exhaust manifold. Once I've got the part it's an evening's job and then I can address the vacuum pipes and see what difference they make to the car's running.
I'm actually quite excited!

I'll endeavour to sort the temperature sensor facility out - if for nothing more than to actually witness them working & see what difference they make!

Keep you posted.

Cheers, Hilton.
Hilton - V12 2+2

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Adamski
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#54 Re: Vacuum Pipes on series 3

Post by Adamski » Tue Aug 07, 2018 7:27 pm

The by pass valves or anti pop valves have an adjuster that can be found under the brass plugs, that I have removed. Assuming the diaphragms are intact and the gaskets sealed you can crank them up as opposed to blanking them. I used a syringe and vacuum gauges to get an idea of what vacuum they were popping at however if you crank the screws up the only effect will be some popping of the exhaust on over run. Much better than having them affect the vacuum and mixture. Alternatively what many have done in the past is to remove the vacuum source to all four but you still need to be sure they aren't leaking. The temperature control valve is best cranked up on all four as it can seriously weaken the mixture if set too slack. They were an emission fudge.
Adam
S3 V12 E Type FHC Manual 1972-owned since 1978

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jagwit
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#55 Re: Vacuum Pipes on series 3

Post by jagwit » Sat Aug 11, 2018 4:22 pm

Best Regards
Philip
71 E-type V12 Coupe,
80 XJS (EFI by Megasquirt & EDIS-6 + 5sp manual overdrive)
73 Jensen Interceptor
74 Interceptor (EFI by Megasquirt + overdrive 4sp auto)

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