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I once again appeal to the brilliant collective mind of the forum to give me an opinion on a slight running fault.

Previous posts provided me with answers  enough to help me renew metering unit and injectors. The latter were KMI brand. I have now had to buy nine new or reconditioned ones, since three of my first replacement six surprisingly turned out to be  faulted 'fresh-from-the-box', after firing up. Only then did the motor run very well, and comfortably rev as far as 5K.   There now remains a persistent niggling  slight exhaust pop at the very split second that the right foot touches the throttle pedal. The fault is greatest when throttling up from a tick over,  but nevertheless happens even at usual roadspeeds..  

If I assume that the injectors themselves are now beyond suspicion, I would like to know if such a fault could perhaps be  consistent  with a maladjustment of the butterflies (I have tried to set these at a near uniform clearance of about 2 thou,  but have not used any flow gauges to properly check);  and/or with  air leak(s)  from the slight but apparent evident wear between 'fly spindles and their bearings in the manifold  casting.  

Many thanks

Mark B.

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Hi Mark

firstly, once you get the PI working properly it will stay that way for ages, as long as you use the car regularly.

i had some issues with mine when i bought it at the end of 2012, it’s run beautifully ever since.

i would recommend setting the throttle butterflies with the flow gauge, and also replacing the throttle spindle linkages and bushes unless they have been renewed already.

these measures are cheap to do and make a real difference.

i’m unsure what you mean by ‘pop’ is there hessitation on opening the throttle or an actual ‘pop’ noise from the exhaust?

whereabouts are you located Mark, someone local might help!

steve

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53 minutes ago, Markboston said:

I once again appeal to the brilliant collective mind of the forum to give me an opinion on a slight running fault.

Previous posts provided me with answers  enough to help me renew metering unit and injectors. The latter were KMI brand. I have now had to buy nine new or reconditioned ones, since three of my first replacement six surprisingly turned out to be  faulted 'fresh-from-the-box', after firing up. Only then did the motor run very well, and comfortably rev as far as 5K.   There now remains a persistent niggling  slight exhaust pop at the very split second that the right foot touches the throttle pedal. The fault is greatest when throttling up from a tick over,  but nevertheless happens even at usual roadspeeds..  

If I assume that the injectors themselves are now beyond suspicion, I would like to know if such a fault could perhaps be  consistent  with a maladjustment of the butterflies (I have tried to set these at a near uniform clearance of about 2 thou,  but have not used any flow gauges to properly check);  and/or with  air leak(s)  from the slight but apparent evident wear between 'fly spindles and their bearings in the manifold  casting.  

Many thanks

Mark B.

Are you certain that the tappets are correctly adjusted and the valves are seated properly? I assume we are talking about spiting back through the inlet manifold or popping in the exhaust. Please advise which it is as it could be an ignition fault?

Bruce.

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Thank you Steve's and Aston. Yes, popping seems within  exhaust rather than up in manifold -and is very brief (one or two  explosions)  only happening the  instant of acceleration. :  Have now ordered a flow gauge from amazon to check butterflies.  Re bushes- was not aware there are bushings in the manifold casting...  But there is some play about spindles.  Will check valve clearances again but believed correct. 

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These are the links and bushes i refer too :post-9473-0-71651700-1494784810_thumb.jpg

 

the original bushes deteriorate and allow a lot of flexing and lost motion, the original linkages are triky to set.

steve

 

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Steve: Thanks again for the quick help and kind photo.   I just checked up from it. The linkage 'gantry' has what look like fairly new white nylon bushes throughout- thanks to the last owner, that is. There is more or less no play at all in the combined movement of this set up, so the air gauge check will be next,  Mark BTW am based in Eastbourne.

Edited by Markboston
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I suspect it is MU mixture. One issue with the Lucas system is that it has no way of transiently enriching the mixture at the instant you open the throttle. When you do this there is a transient lean spike in the mixture. Some carbs cover this with an accelerator pump which literally squirts fuel into the engine. EFI systems cover it by transient enrichment at initial throttle openings.  Lucas and triumph attempted to get around this issu with PI by setting it on the rich side, which is why when you follow a PI car it can smell like a petrol station. It is possible that yours is running too weak to cover this transient lean period. Two reasons for this couple be:

1) an air leak in then manifold (or around the injectors)

2) the MU set a little to lean. 

I experimented with my MU which was rebuilt and set up as standard by Neil Ferguson.  I was actually able to lean out the mixture a little from standard (giving marginally better mpg) but if I went to far the first sign was popping on snap throttle opening. 

Tim

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My timing was out due to the marks on the pulley no longer being accurate, I used a simple plastic screw in piston stop so I could find TDC and then set it up correctly from there, and used the adjuster on the distributor to fine tune for the current fuel.

Gareth

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Tim thank you very much for that. Yes, as you now point out, the fault is rather like having a carburetter set slightly too lean. I do not yet know how to adjust the mixture - the M unit is a new exchange from Rimmer. Once I have checked the air flows for balance I will do some homework on MU adjustment. I am only just beginning to realize how simplistic  the Lucas system actually is.  But I am sure as you mention there must be  air-leaks via the butterfly spindles -which presumably cannot be fixed except by heroic intervention - and which might be causing a too-lean mixture at the first instant of acceleration. The plugs, btw, are a light biscuit and in themselves look acceptable by the old standards of colour and deposits I believe. Mark.

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Very valid point on timimg, i made a tdc tool out of an old spark plug and my pulley marks were 8 degrees out.

so you might try retarding the ignition a little and see if this cures.

good point also on the lean mixture, these setups need to run a little rich as explained.

i get about 25mpg in normal use, 30 when driving like a granny and 20 when ‘enthusiastic’, this is with appropriately rich mixture

keep at it Mark, very rewarding when you fix it !

steve

 

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post-9473-0-54928800-1514739882_thumb.jpeg

tdc tool, spark plug with big bolt araldited in and rounded end.

inset, rotate crank gently clockwise to touch, mark pulley.

rotate crank anti-clockwise to touch, mark crank

tdc is midpoint between marks

simples!

steve

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No Problem Mark...

The system is pretty simple, but adjustment without a good reading of mixture is risky. I have an air-fuel meter that goes on the end of the exhaust. This is invaluable as you see the real time mixture as you drive and when you adjust the MU you can actually see what you have done. Saying that, as far as I remember richening the mixture at high manifold vacuum (e.g. Closed throttle) is a case only changing one of the settings.

Cheers

Tim

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On 2/27/2019 at 2:15 PM, Markboston said:

I once again appeal to the brilliant collective mind of the forum to give me an opinion on a slight running fault.

Previous posts provided me with answers  enough to help me renew metering unit and injectors. The latter were KMI brand. I have now had to buy nine new or reconditioned ones, since three of my first replacement six surprisingly turned out to be  faulted 'fresh-from-the-box', after firing up. Only then did the motor run very well, and comfortably rev as far as 5K.   There now remains a persistent niggling  slight exhaust pop at the very split second that the right foot touches the throttle pedal. The fault is greatest when throttling up from a tick over,  but nevertheless happens even at usual roadspeeds..  

If I assume that the injectors themselves are now beyond suspicion, I would like to know if such a fault could perhaps be  consistent  with a maladjustment of the butterflies (I have tried to set these at a near uniform clearance of about 2 thou,  but have not used any flow gauges to properly check);  and/or with  air leak(s)  from the slight but apparent evident wear between 'fly spindles and their bearings in the manifold  casting.  

Many thanks

Mark B.

Hi Mark!

2 years ago I bought I bought 6 re-con injectors from Moss, 4 failed very quickly, they were KMI ones. So having dealt with KMI in the past I spoke to them directly. The fault was they were not holding pressure due to the ' O' rings being of the wrong compound and they s/b green in colour and not black. It turned out that they were very oil stock as KMI had changed the compound 3 years before. Moss were selling old stock? They were all changed and no problems since, therefore where did you buy yours from? I would check yours?

Bruce.

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Hi Bruce, Mine came from Rimmers. I did call them to ask if faulted units were often seen,  but was told a rarity. Of course  I did not want to make too much fuss- its incredible even to be able to buy parts for 50 year old cars off-the-shelf so easily,  in the larger picture!  But three out of six being  faulty and I'm not so sure that standards of the original equipment are quite maintained.... I expect you, like me, have bought 'Lucas' ignition condensers from China that simply do not work at all... and the spring on a recent set of  contact points was so mis-shapen that it craftily shorted itself out.. took me ages to realize..  Mark 

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For injectors i would recommend having them reconditioned by Neil Fergusen

he’s super helpful, reasonably priced, and quick to ship

i’ve had two sets in two cars, present ones running faultlessly for 8 years now!

steve

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21 hours ago, Markboston said:

Hi Bruce, Mine came from Rimmers. I did call them to ask if faulted units were often seen,  but was told a rarity. Of course  I did not want to make too much fuss- its incredible even to be able to buy parts for 50 year old cars off-the-shelf so easily,  in the larger picture!  But three out of six being  faulty and I'm not so sure that standards of the original equipment are quite maintained.... I expect you, like me, have bought 'Lucas' ignition condensers from China that simply do not work at all... and the spring on a recent set of  contact points was so mis-shapen that it craftily shorted itself out.. took me ages to realize..  Mark 

Hi Mark,

The points & condenser issues are well known, this why I would only deal with the DD on this subject. Regarding injectors the 'O' ring compound is critical as modern 99 octane V Power is very aggressive and there has to be a good knowledge of Aerospace compounds that are resistant to liquids like Skydrol which has a habit of destroying most rubber type compounds. Therefore I would be happier if PTFE 'O' rings were used instead of Viton type B. Years ago when I was sent to CAV on an apprentice exchange scheme, CAV then were thinking about using PTFE 'O' rings as they manufactured the Lucas injectors and there were too many returns with 'O' ring faults and that was using leaded fuel in those days.

Bruce.

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Well done  to all unseen register friends for so kindly helping with your knowledge and experience. I am delighted to say that the present issue was fixed by following your advice.

Having bought an STE air gauge (Amazon 40 quid) I checked the flows. Much disparity between the throttle pairs, even though I had previously attempted to set the butterflies  with about a 2tho gap to the choke wall. Just a little adjustment on the control links made big differences to the air flow. But I think the real culprit was a butterfly (number 4) which was not neatly tightened down on the arbour and had sort of shifted by an invisible fraction to allow about 4 times as much air to pass as its pair. Presumably this made a local weak mixture, with exhaust pop, every time the gas pedal was touched. I fixed it by backing off the two retaining screws and wedging the fly shut against a 2 thou feeler. The engine seems to perform much more smoothly, and without predictable backfire, as can be imagined. The car had a six into one stainless  single-bore exhaust system put on it by the last owner. I am not a fan of  the hollow gurgling sounds these make on the overrun - too much like a motorbike for my ears- but the car itself behaves  fabulously well now,  Many thanks until the next crisis! Mark.

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