Jumping and spitting under acceleration

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Holeshot
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#1 Jumping and spitting under acceleration

Post by Holeshot » Fri May 18, 2018 9:41 am

I've got a bit of a conundrum and need your expert advice!

Recently the car's been running a bit lumpy/sluggish and spitting a bit til really warmed up, so I when checking the diaphragms in the Strombergs, I found one had a tiny split so I thought "Bingo!! This is it!" Replaced it and all seemed good upon start up, with it running better than it ever has - lovely and smooth. Then I took it for a test drive and the lumpiness had gone and it seemed more lively but the spitting seems to have manifested itself more because of this.
It seems to rev more eagerly, but sometimeseven under gentle acceleration, it hesitates/jumps and spits - sometimes quite badly.
I checked the dashpots and in one, the oil seems to have emulsified. I'll change the oil in it this evening and take it for a drive but can't think that this will improve things but would be interesting to see if it goes milky again - I wonder what would cause this? Also, the carb slide/piston was quite blackened.
Also when I came back from the test, the lower exhaust pipe was blowing a bit more from the lower manifold joint, but don't think this would cause anything other than some popping on the overrun....or would it?

I'm baffled - can anyone help me please?

Cheers,
Hilton.
Hilton - V12 2+2

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jagwit
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#2 Re: Jumping and spitting under acceleration

Post by jagwit » Fri May 18, 2018 11:05 am

What ignition system does your car have?
Best Regards
Philip
71 E-type V12 Coupe,
83 DD6, 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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#3 Re: Jumping and spitting under acceleration

Post by Holeshot » Fri May 18, 2018 11:51 am

It's the original standard one (sorry, can't remember the make)
Hilton - V12 2+2

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#4 Re: Jumping and spitting under acceleration

Post by jagwit » Fri May 18, 2018 3:04 pm

In that case it will be the Lucas OPUS system - notorious for the trouble it brings with old age.

Regardless of what the actual cause is of your trouble, please consider upgrading the ignition system to a modern one by default for reliability and peace of mind. The easiest upgrade is to fit the used dual coil ignition system (dissy, dual coils and ignition module) from an HE XJS or XJ12 or Daimler Double 6. This is basically a "plug and play" solution. Doing so also gives you the benefit of getting vacuum advance which will decrease fuel consumption by at least 20% (open road). Some will vehemently insist that you MUST drill one carb to get so-called "ported vacuum" but I am just as convinced that is not necessary (unless you HAVE to meet certain emissions tests). I run my car with vacuum supplied directly from the manifolds and it runs fine under all circumstances.

Another option is to replace the OPUS electronic bits of your existing distributor with modern electronics like Lumenition or Pertronix etc. You should consider to also get a vacuum advance module to replace the vacuum retard module on your car (if you want that economy gain). My own V12 E has the Lumenition upgrade and runs sweetly (installed by previous owner.)
Best Regards
Philip
71 E-type V12 Coupe,
83 DD6, 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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#5 Re: Jumping and spitting under acceleration

Post by Holeshot » Fri May 18, 2018 6:26 pm

Thanks so much.
Yes, I’ve often thought about replacing for a modern version but I use the car so irregularly and when I do use it, it runs OK and the moment passes.
Proabably time to think a bit more seriously about it now.

Really interesting to hear your thoughts about it.

From how the car’s behaving, it just seemed to me that it was the carburation that was the problem, but that may not be the case.

Thanks again 🍺
Hilton - V12 2+2

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#6 Re: Jumping and spitting under acceleration

Post by 42south » Fri May 18, 2018 8:21 pm

Hi
The classic Opus failure mode normally doesn’t start until after the amplifier warms up.
Your problem is with a cold engine so may indeed be carburettor related, have you looked at the colour of your plugs? On my V12 if I put the choke in too early when cold, the car will spit back through the carbs on acceleration.
In my opinion the best option for ignition upgrade is the kit offered by SNG, with this you get a rebuilt HE distributor, new ballast resistor and coil, and the later HE amplifier chip nicely packaged in an original pre HE casing. You may think this looks expensive, but you do get money back when you send in your old distributor and amp. Also if you buy second hand bits as Philip suggests, the distributor will almost certainly need rebuilding.
Regards
Mark
I just reread your post and another possibility came to mind. when the orings in the bottom of the dashpot oil tube failed in mine to the extent that they wouldn't hold oil, I had the symptoms that you describe, backfiring etc with any attempt to accelerate.
The guy who looks after mine reckons that ATF fluid is better than oil for the dashpots. similar viscosity to the recommended oil which is 30wt(I think).
Mark Brown
1971 S3 Etype
When my ship comes in it will probably be at the airport.

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#7 Re: Jumping and spitting under acceleration

Post by Holeshot » Sun May 20, 2018 10:44 am

Thanks for the replies and advice so far guys, and I’m sorry that the info I’m giving may be a bit muddled.
Anyway, here’s an update after replacing dashpot oil and another diaphragm and also giving the distributor a brush up and drop of oil. Checked the plugs and they’re a perfect shad except for one which was a bit oily (one serviced by the carb with the now new dashpot oil.

So....It starts well. Runs OK when under choke with the usual hesitancy until corrected by the right choke setting, but generally running acceptably (though an occasional tiny spit under mild ‘warming-up’ acceleration which I wouldn’t normally find worrying).
However, when the cars getting warmer, the spitting gets progressively worse to the point where I only dare use the lightest of throttle for fear of super-jumpiness/embarrassment in traffic. This combines with an erratic running of bad response and flatness.
In summary, not a pleasant drive.

Reflecting on both Philip & Mark’s advice above(thanks guys) I’m now accepting that it may well be the ignition system. I’m not convinced that carbs can slip so far out of whack in such a short period(mileage-wise) other than rubber components perishing or dirt blockages whereas its more likely ignition components deteriorate over time(car doesn’t do many miles but languishes in a garage). It just seems more like the ignition is the culprit.

I’m now thinking that I will heed your advice and am considering the SNG Barrett ignition replacement kit which even if it isn’t the fix for the problem will ultimately address the hot start issues this car has always been vulnerable to. Advice on this would be most welcome!! At least in fitting this, it will eliminate the ignition from the equation if the problem continues?

Btw Mark...I’m not sure where the O-rings are at the bottom of the dashpot oil tube are. Looked on the carb diagram but couldn’t figure them out, sorry.

Anyway....will take it for a spin today just to see if anything else manifests itself to give more of a clue. But to be honest, I don’t really like taking it too far as I’m starting to worry it may not get me back!!!

Thanks again.
Hilton.
Last edited by Holeshot on Sun May 20, 2018 4:20 pm, edited 1 time in total.
Hilton - V12 2+2

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#8 Re: Jumping and spitting under acceleration

Post by jagwit » Sun May 20, 2018 11:36 am

Holeshot wrote:
Sun May 20, 2018 10:44 am
I’m now thinking that I will heed your advice and am considering the SNG Barrett inhibition replacement kit.

I don’t really like taking it too far
If you do go this route, I believe (on hearsay) that the SNG dissy comes standard with a vacuum RETARD module - exactly like the original. This is good if originality is your thing but its bad from an efficiency / fuel economy perspective. (Weirdly, the retard module is what was needed to meet the emissions specs of those days)

If you want the benefits that vacuum advance can bring, I think you may have to purchase the vacuum advance module as a seperate item.

Once its sorted, there is no reason you can not take the V12 cross-continent all the way to Japan. Mine is like that.
Best Regards
Philip
71 E-type V12 Coupe,
83 DD6, 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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#9 Re: Jumping and spitting under acceleration

Post by angelw » Sun May 20, 2018 12:24 pm

Hilton Wrote:
I’m not sure where the O-rings are at the bottom of the dashpot oil tube are. Looked on the carb diagram but couldn’t figure them out, sorry.
Hello Hilton,
The O ring sits in an annular groove in the circumference of the Metering Needle adjusting screw (brass screw). You will find this screw at the bottom of the bore of the Dash Pot Tube. It has a dished, star type washer, the points of its legs an interference fit in the bore of the tube, sitting directly above the screw. This star washer supplies resistance to the movement of the screw, so that when it is turned Counter Clockwise (viewed from open end of bore), it moves the Metering Needle toward the bottom of the carburetor.

To renew this O ring, obviously the Metering Needle adjusting screw needs to be removed from its location at the bottom of the Dash Pot tube. Proceed as follows:

1. Remove Air Piston from carburetor body and clean thoroughly, paying particular attention to where the Metering Needle is housed in the face of the Air Piston.

2. Remove Metering Needle retaining grub screw (small Minus Screw Driver required). See attached picture below for location.

3. Use special tool, shown in attached pictures below to eject Metering Needle until the thread of the adjusting screw has disengaged with the internal thread of the Metering Needle. The screw will be turned in a Counter Clockwise direction (viewed from open end of Dash Pot bore) to move the Metering Needle in ejection direction. It won't move vary far; perhaps 5mm. If the adjusting screw is hard to rotate, soak the assembly in carburetor cleaner to help loosen any dried fuel varnish and carbon that may be holding it.

4. Once the adjusting screw has disengaged from the end of the Metering Needle, attempt to withdraw the Metering Needle from the face of the Air Piston. It may be necessary to reengaging the adjusting screw and move the the Metering Needle in and out axially to allow it to move freely in its bore. Once the Metering Needle is moving freely, eject it as far as possible and withdraw using fingers, or by any means available to you that will not damage the Metering Needle in any way.

5. With the Metering Needle removed, arrange the Air Piston vertically (Metering Needle bore upper most), with the Dash Pot end of the aluminum body of the Air Piston supported.

6. Use a length of hardwood dowel, slightly smaller in diameter than the bore from whence the Metering Needle was removed, to either drift or press the adjusting screw along the length of the Dash Pot tube until the retaining star washer and the adjusting screw can be recovered from the end of the tube.

The retaining star washer is slightly dished, with the bottom of the dish facing the bottom of the Dash Pot Tube. This is ideal for installing the washer in the Dash Pot tube, but not so good when removing it. The points of the legs of the washer tend to try and dig into the bore of the Dash Pot Tube and cut shallow grooves in the bore. This is a common occurrence when performing this operation and hard to stop from happening, once its started. About all you can do is lube the bore well with sticky lubricant containing a high degree of Extreme Pressure additives.

Once you have the adjusting screw in your hand, the method of replacing the O ring will be obvious.

Regards,

Bill

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#10 Re: Jumping and spitting under acceleration

Post by 42south » Sun May 20, 2018 9:49 pm

Hi Guys
Hilton to answer your questions

Hot starting, is improved with the SNG kit, but the best technique I find is to try a start holding a little accelerator, if this doesn't work then push the accelerator to the floor and crank till she starts with a satisfying roar, generally about 2-3 seconds of crank.

Dashpot Oring, Bill has given an excellent account of how to go about replacing the Orings, best to do all 4 at once. They are available through SNG, buy the little star washers as well.
You didn't mention whether your dashpots still hold oil, this would explain the symptoms if they don't.

The SNG distributor kit. yes it does still have the retard vacuum module as per the original. I would get the kit fitted first then in the future look to changing to a vacuum advance module, one change at a time. There is plenty of advice on the forum if you search.
Mark Brown
1971 S3 Etype
When my ship comes in it will probably be at the airport.

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#11 Re: Jumping and spitting under acceleration

Post by Holeshot » Mon May 21, 2018 11:39 am

Again, thanks for the great replies - so nice to get this response - I think we all know how comforting it is to get help when you're trying to figure something out that you're confused about, so cheers guys :drinkingcheers:

Thanks Bil for the impressive explanation of the O-ring situation.
I've checked and it seems as though mine do actually retain the oil sufficiently, so I think best not to touch these for the moment, but thanks for taking the time to post such brilliant instructions.

I've just placed an order with M.C Wilkinsons for their Ignition Replacement Kit. SNG Barretts had a 6 week+ wait. I trust these are much the same units.
I'll receive this tomorrow so hope to get it fitted quickly and fingers crossed for a positive result.

Mark - I've tried every which way to start the car when hot(after being left for an hour or so) and although sometimes it would start OK, mostly it was a heart-in-mouth moment when turning the key as generally it would be a full 60 second whirring starter motor moment hoping the battery wouldn't wind down, followed by a massive sense of relief when it would stutter into life......usually with an audience just to add a bit more stress!
Like you mention, the foot-to-the-floor method seemed to just about do it in the end, accompanied by mentally praying to my God of choice...
As you advise, I'll fit the kit and see if I feel the need for vacuum advance module - thanks for the support.

I'll let you all know how the Ignition swap goes - hopefully useful for anyone embarking on a similar choice.

Cheers,
Hilton.
Hilton - V12 2+2

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#12 Re: Jumping and spitting under acceleration

Post by Holeshot » Tue May 22, 2018 10:58 am

Super service from MC Wilkinsons.

This arrived this morning (next day delivery) and turns out it's the SNG Barrett item - same price etc.
It's a glorious thing to behold.....bit like Christmas!
I removed the old system last night so am just a little bit excited about getting going on this.
Will keep you posted.
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#13 Re: Jumping and spitting under acceleration

Post by jagwit » Tue May 22, 2018 11:23 am

Excellent!! I do hope that you will find an immediate improvement.

That vacuum retard module on the side of that dissy is such a horrible thing :thumbdown: . I become nauseous just looking at it.

No wonder that V12 E-types are so notoriously thirsty....
Best Regards
Philip
71 E-type V12 Coupe,
83 DD6, 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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#14 Re: Jumping and spitting under acceleration

Post by Holeshot » Tue May 22, 2018 11:32 am

jagwit wrote:
Tue May 22, 2018 11:23 am
Excellent!! I do hope that you will find an immediate improvement.

That vacuum retard module on the side of that dissy is such a horrible thing :thumbdown: . I become nauseous just looking at it.

No wonder that V12 E-types are so notoriously thirsty....
You'll be the first to know Philip!
My heart will be in my mouth on the test drive :wow:

LOL at the pesky VRM!! Sorry to taunt you with it :wink:

Cheers,
Hilton.
Hilton - V12 2+2

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#15 Re: Jumping and spitting under acceleration

Post by 42south » Tue May 22, 2018 9:19 pm

Hi Hilton
The Amp mounts in the valley where the original was. Don't worry about this as the internals of the amp are now a GM solid state chip, not the original style circuit board with its heat sensitive components. So the comments about moving the amp to the front of the engine for extra cooling dont apply to this amp.
Heaven forbid that you should ever have another amp problem, but the internal chip is available on the internet for around $25USD.
Cheers
Mark
Mark Brown
1971 S3 Etype
When my ship comes in it will probably be at the airport.

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#16 Re: Jumping and spitting under acceleration

Post by Woolfi » Tue May 22, 2018 11:16 pm

"Some will vehemently insist that you MUST drill one carb to get so-called "ported vacuum" but I am just as convinced that is not necessary (unless you HAVE to meet certain emissions tests). I run my car with vacuum supplied directly from the manifolds and it runs fine under all circumstances."
This is 100% wrong. If you have an advance capsule and the rubber hose is attached BEHIND the carb, the vaccuum is max at idle. Therfore you will have 10 degree plus 16 degree = 26 degree pre ignition before TDC. But the motor need sroundabout 10 degree at idle.
By opening the butterfly the vaccuum will drop and the amount of preignition will decline. The motor is saving gas, if the preignition is rising with opening the butterfly . After a certain point, the preignition shall decline. Otherwise there will be knocking.
In my own EV12 the privious owner has mounted a advance capsule and connected to the vaccuum behind the carb. Because of roundabout 25 degree of preignition at idle, the idle was very bad. I was searching for nearly three years, why the idle was bad.
Regards Wolfgang Gatza

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#17 Re: Jumping and spitting under acceleration

Post by 42south » Tue May 22, 2018 11:39 pm

Hi Woolfi
This topic has had lots of discussion on the board.
I had my carb ported as per the original Jaguar idea which has the port on top of the carb entering the carb just ahead of the butterfly on the air cleaner side.
This gives little or no vacuum at Idle, moderate vacuum at part throttle cruise, which is where you want the extra ignition advance, and very little vacuum at wide open throttle, which is where you dont want too much advance.
If you made a big mistake and connected the advance vacuum unit to the retard port, which is underneath the left rear carb and enters the carb behind the butterfly, on the engine side, then you would get the conditions you describe.
Here is a link I found with pictures of the porting

http://www.pclarkson.plus.com/Ignition3.html

Or have I misunderstood your post?
Cheers
Mark
Last edited by 42south on Wed May 23, 2018 9:49 am, edited 1 time in total.
Mark Brown
1971 S3 Etype
When my ship comes in it will probably be at the airport.

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#18 Re: Jumping and spitting under acceleration

Post by jagwit » Wed May 23, 2018 7:45 am

Hilton, I post the following mainly for amusement value (us petrol heads can be too serious at times) but at the same time there is some underlying seriousness as well which may result in your thread being "hijacked". This is your thread on your topic, so at least from my side I will try to avoid this from happening.
Woolfi wrote:
Tue May 22, 2018 11:16 pm
Philip Lochner wrote:"Some will vehemently insist that you MUST drill one carb to get so-called "ported vacuum" but I am just as convinced that is not necessary (unless you HAVE to meet certain emissions tests). I run my car with vacuum supplied directly from the manifolds and it runs fine under all circumstances."
This is 100% wrong.
Thank you Wolfgang!!! :lol: I was beginning to worry that nobody would "vehemently insist" for ported vacuum....

Now let's see how much confusion and amusement can result by how much I AGREE with you. :mrgreen:

Woolfi wrote:
Tue May 22, 2018 11:16 pm
If you have an advance capsule and the rubber hose is attached BEHIND the carb, the vaccuum is max at idle.
I fully agree.

Woolfi wrote:
Tue May 22, 2018 11:16 pm
Therfore you will have 10 degree plus 16 degree = 26 degree pre ignition before TDC.
I fully agree (IF the engine was set to 10º without vacuum advance and if full vacuum advance adds 16º)

Woolfi wrote:
Tue May 22, 2018 11:16 pm
But the motor needs roundabout 10 degree at idle.
I agree - with one minute change:

But the motor needs roundabout 10 degree at idle speed.

Woolfi wrote:
Tue May 22, 2018 11:16 pm
By opening the butterfly the vaccuum will drop and the amount of preignition will decline.
I fully agree. (I presume this statement relates to my case where the vacuum advance is connected to full manifold pressure?)


(I presume the following applies to the case where we have ported vacuum)
Woolfi wrote:
Tue May 22, 2018 11:16 pm
The motor is saving gas, if the preignition is rising with opening the butterfly . After a certain point, the preignition shall decline.
I fully agree.

Woolfi wrote:
Tue May 22, 2018 11:16 pm
Otherwise there will be knocking.
I fully agree.


So.....!!!! It seems that I have agreed with everything you said, yet I stand by my view. So where do our views digress then??? :scratchheadyellow: :?: :bigrin:
Best Regards
Philip
71 E-type V12 Coupe,
83 DD6, 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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#19 Re: Jumping and spitting under acceleration

Post by Holeshot » Fri May 25, 2018 10:15 am

Well, I fitted the kit last night and started her up briefly.
All sounds good and seems to be working OK.
Strangely, it seems quieter.....and this was inside the garage too! Hmmmm....

I didn't get a chance to warm up the engine as it was quite late, but next I'd like to set the timing with a strobe.

With a cursory look last night, I couldn't readily see the timing plate, but any tips or pointers would be very much appreciated in locating it and the subsequent timing process.

Quite relieved it started tho 8-)
Hilton - V12 2+2

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#20 Re: Jumping and spitting under acceleration

Post by jagwit » Fri May 25, 2018 1:24 pm

Well done Hilton!

The different sound could be the result of the timing being different. It could also be that its getting better and more consistent spark. Fact is something did change.

Now for tuning:
The timing mark is obviously on the crank pulley and the reference plate is mounted to the sump underneath the crank pulley. Yep, you need a pit, or a lift, or ramps, or jack up the front of the car to be able to set timing.

1) With vacuum pipe to dissy disconnected and plugged;
2) Set timing to whatever the manual specifies (which is 4º AFTER TDC with engine idling, or 12º BEFORE TDC with engine stationary).

I presume 4º ATDC is with vacuum connected to the vacuum retard module (manual does not specify this). Here you can already see how BAD that vacuum retard curse is!! Your engine will be better off (more efficient) just not connecting the vacuum pipe at all - ever. You can confirm this by connecting and disconnecting the vacuum line to the vacuum retard module. You should find that the engine picks up speed when you disconnect it and will drop in idle speed when you connect it. Anyone willing to have a go at explaining WHY this happens?

My recommendation (if you are willing to accept the African's recommendation, the same one who seemingly, erroneously believes that ported vacuum is not needed :roll: ) is to set the timing to 12º BTDC with engine idling and vacuum disconnected (permanently, until you fit the vacuum advance module.)

3) It would be prudent to also re-set the carbs at this point - if you can (or knows someone who can - who REALLY can... and setting by ear does NOT qualify as "REALLY"....) If they don't have some decent, operational carb balancing gauge and know how to use it, stay away.
Best Regards
Philip
71 E-type V12 Coupe,
83 DD6, 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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