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Wondering if you guys could help me w some advice. 

I got my MU rebuilt by Prestige a few months back.  Reinstalled by a local outfit and since then the TR has been running beautifully smooth when cold but as she warms up, runs like a pig, especially when under load.  Almost undrivable.

Taking the TR to another group who specialise in race spec'ing and rebuilds, it turns out the MU which was holding vacuum before, isn't now. 1st assumption was the diaphragm (would have been somewhat disappointing following a recondition) but seems it is actually leaking at the threads around the top (as indicated).

Should this be something that is expected after a rebuild? Something my local outfit should have looked at or should I expect that a unit sent literally across the world should not have "teething issues" like this.  Essentially: how much tuning is still required after these are rebuilt?

Cheers all

Matt the kiwi

 

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Hi Matt,

Sorry to hear of your problems. I'm surprised there is leakage at the cap retaining screws after a reconditioning. I'm sure Prestige would have tested for vacuum before sending it back to you. Are you sure nobody "tuned" it during installation? I'm always amazed at how many people think they can improve the tuning using the concentric adjustment screws under that tempting-to remove cover!

Anyway, should be pretty easy to fix. A bit of threadlock on the screws and Bob is your proverbial. The screws only hold on the cover so, even if the threads are totally stuffed by a monkey over-tightening them, you should be able to achieve a vacuum seal. BTW there's no need for an airtight seal between the cover and control unit body, only around the threads.

Good luck from over the Tasman,
John

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Peter Bower in Sydney rebuilt my MU and injectors about 3 years ago. They were tested and calibrated on his bench test equipment before they were returned  .

I just  reinstalled the MU & injectors , bled  the injector lines and did a final tighten of the keeper plates. The engines run perfectly ever since.  

Amongst Peter's test reports was one detailing my MU's fuelling rate vs manifold vacuum so I would imagine his vacuum test rig would have picked up leaks like caused your problem- I suspect your leak was masked by the cold enrichment lever.

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Matt,

Don't forget that the vacuum hose connections can leak into the same compartment, and that an old hose can leak along its length.

The cover over the adjustment lock nuts, as shown in your pic, is held down by two set screws, whose thread does communicate with the depression chamber, but there is no other way through, save for the bush that carries the adjusting screws.   There is no need for a gasket on the cover, so if it is the screw threads that are leaking, then some sealant, loctite or perhaps some teflon tape, should do the trick.

John

PS Ah! JohnC is ahead of me!  Do you have the Lucas Pi manual?   It's online at http://www.lucasinjection.com/MANUALS.htm or the Wheatsheaf Press in Cheshire, UK used to sell facsimile copies. 

Edited by john.r.davies
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10 minutes ago, john.r.davies said:

Don't forget that the vacuum hose connections can leak into the same compartment, and that an old hose can leak along its length.

Good point. If the hose connections leak (or the hose itself) it would give the same symptom. As the engine needs a richer mixture when cold that could explain why things are good when cold but bad when hot.

John

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The holes in my cap have been filled with Araldite, but make sure the screws that hold the black cap on are not too long and push the plugs out again, I have also made a gasket for the top black cover, from a bike inner tube as I could never get the 3 screw adjusters inside air tight. Just nipped up enough to make further adjustments.

Checked with a vacuum pump at the manifold.

John

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17 hours ago, john.r.davies said:

There is no need for a gasket on the cover, so if it is the screw threads that are leaking, then some sealant, loctite or perhaps some teflon tape, should do the trick.

Sorry my bad: seal leak is indeed in the screw threads underneath, not the cover itself.

17 hours ago, john.r.davies said:

Don't forget that the vacuum hose connections can leak into the same compartment, and that an old hose can leak along its length.

Understanding is that they excluded this and leak was sorted with sealant on the threads like recommended above.  A new hose might be in the off'ing in near future anyway.

17 hours ago, Mike C said:

Amongst Peter's test reports was one detailing my MU's fuelling rate vs manifold vacuum so I would imagine his vacuum test rig would have picked up leaks like caused your problem- I suspect your leak was masked by the cold enrichment lever.

Never saw this and maybe that's part of my question.  Leak must have been masked by the cold enrichment as you say and was much, much worse when the car had been in traffic. I thought initially that this might be a dodgy fuel pump, but in retrospect the in the heat the MU threads may have opened enough to unmask the leak fully.  What I'm confused by is why the leak exists when it didn't previously and whether it's a rebuild thing or something I should fairly expect a garage who are familiar with Triumphs to know about.  I'm somewhat irked that I've sent a unit off to Wales to get fixed and it's come back both better and much worse.  Yet it's taken a team familiar with elderly cars and race cars a few days to track down the issue even though they've never seen Lucas PI before and asked for all the manuals so they could get properly familiar with it!

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Hi Matt,

the MU leaks at several positions, especially at the banjo in the middle of the diaphragm,

the two bolts that hold the cap and the three setting bolts under the cap. Besides the big cap to mu body

hold down with 4 bolts nothing should leak because it is sealed with the round edge of the diaphragm underneath.

 

Up to a normal amount leaking is pretty normal and is compensated by the suction of the manifolds.

The question what remains is "What is normal" difficult to judge from here but I would see the problem

not in this area. Definitely if okay there is nothing to feel or hear when engine is running.

 

My first recommendation to far away friends is to buy a complete ignition system from simon bbc,

complete with a Lucas sports coil and high tension leads to test. Take it with points and it will be under

100 Euros. Plug this in with a separate 12V line from the battery to first make sure the problem is not

ignition related.

 

My second recommendation is to fit a wideband AFR sensor to find out what goes on when engine is cold

and what will differ when getting warm. The easiest solution can be a locked enrichment system what can be

starting under the square plastic plate beside the mu where the lever arm is located. Does it fully come back

to the full load setting screw at the bottom?

 

You may remove the injectors and let the pump running. Check if they keep tight and do not let fuel. That is an indication of a problem with the sealing inside the mu.

 

Good luck and keep us informed!

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Matt,

Recall that Lucas Pi regulates fuel supply according to inlet vacuum.    The less the vacuum the more fuel, in other words the more open the throttles, the more fuel is injected.

So a leak into the depression chamber is interpreted as Wide Open Throttle, all the time.     Fine, if the engine is cold, but far to rich except at WOT at any other time.    I had a similar problem, started well, idled fine, but stumbled and missed when warmed and used on the public road, UNLESS I used WOT.     Turned out to be that the choke cable was jamming and holding the choke lever open.   Those symptioms so similar, is it worth checking that your choke cable closes the lever fully?

 

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17 hours ago, john.r.davies said:

Those symptioms so similar, is it worth checking that your choke cable closes the lever fully?

Thanks JRD. It does close fully, had been checking off the “usual suspects” mentioned on the forum

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1 hour ago, matttnz said:

Thanks JRD. It does close fully, had been checking off the “usual suspects” mentioned on the forum

Have you checked your idle vacuum by say connecting a vacuum gauge to the brake booster connection? Mine has been at 10 inches Hg since the engine was built up in the mid 1990's. Peter Bower needed the vacuum figure and the fact that my engine displacement is 2.7L to recalibrate my MU.

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The team who are working on it have done so and confirmed it was leaking, solved by sealant (assuming loctite or similar) across the threads.

This does raise whether the MU needs calibration or whether it was done but unfortunately I received no such documentation as you did (and New South Wales is a h**l of a lot closer than Old North Wales... :/ ).  I figured that sending it to the people who know these best would give me the best chance of a well setup MU for the next 10y or so.  Perhaps I was wrong.  The accepted wisdom I've taken is that if you send it to people who know what they're doing: all is well and don't touch it.  However, having tried this option, EFI conversion is looking awfully tempting... Would make it the only local EFI and I'd be the "learning experience" in NZ.

As far as I know the engine hasn't been bored out.  It was reconditioned in the late 90s and hasn't covered many miles since (20K or so and many by myself).  Compression is still quite even and no thrust float so I'm figuring it's got some miles left before I need to play there.

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There should be minimal leakage down the screw threads that hold the cap on.

The cap does not itself form a seal - it’s there to stop tampering with the mixture adjustment mechanism. If the screws are missing then there will be a significant leak, enough to affect the mixture. The sealant on the screws is more about indicating tampering for warranty purposes.

Other parts of the metering unit can leak. Check the vacuum pipe and if it is ok the metering unit seal should hold to the “tongue test” Suck on the pipe, hold your tongue against it and the vacuum should hold for while. If it does seek other causes of running rich such as vacuum leaks elsewhere and the max fuel lever holding on. The rollers can come off the inside but hard to confirm without disturbing the warranty seals.

 

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39 minutes ago, Andy Moltu said:

There should be minimal leakage down the screw threads that hold the cap on.

The cap does not itself form a seal - it’s there to stop tampering with the mixture adjustment mechanism. If the screws are missing then there will be a significant leak, enough to affect the mixture. The sealant on the screws is more about indicating tampering for warranty purposes.

Other parts of the metering unit can leak. Check the vacuum pipe and if it is ok the metering unit seal should hold to the “tongue test” Suck on the pipe, hold your tongue against it and the vacuum should hold for while. If it does seek other causes of running rich such as vacuum leaks elsewhere and the max fuel lever holding on. The rollers can come off the inside but hard to confirm without disturbing the warranty seals.

 

The original M/Us had a grey sealant on those screws applied by the factory as I have a genuine Lucas re-con M/U as a spare?

Bruce.

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Given that your local team has isolated the screws as the problem, is all well now? If you ever do remove the screws, it might be worth checking that they are actually the right ones...

BTW +1 for Peter Bower here in Sydney. He's a lovely bloke and, more importantly, really knows his stuff around old PI systems of many types. You can find him here.

John

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Hello Matt, I am also in AKL/Whangarei NZ with a TR6 with MU problems so may be able to help. Firstly are you in the NZ TR Register as the Technical chap Ken is absolutely brilliant at helping and very experienced (with around 6 TRs of his own to maintain), so can I suggest you contact him for help locally. secondly and after Kens help with my two MU's active plus spare, I believe that these should be setup by the OH facility which perforce must have a test bench for that task, and after this the unit should only require installation, timing to the engine and no other adjustments should be needed. This assumes an engine pulling good vacuum which mine wasn't.  As you found with the screws leaking (mine did likewise) these cars a a bugger if the vacuum is not there as they go to full rich and quickly wet plugs - lose ignition and its all over really. I have a permanently installed vacuum gauge now, and after head overhaul with new valves guides rockers shaft etc I now have good vacuum close to 9in Hg. The other problem area in my experience is the 6 butterflies and multiple linkages making it very hard to set up. I am looking to install an improved mechanism in due course.  Let me know prmwilsonatgmaildotcom if I can help locally.  Cheers Peter   JohnC thanks very much for the link to Peter Bower - I now have someone to send my MUs. Great.

 

PS does anyone out there know how much end float you should have on the rotating sleeve of the MU - un installed and push/pull on the drive end - I am getting quite a few mm yet cannot see how this is normally controlled. Ok normally the metering end is pushing back but that doesn't seem a satisfactory result. Thanks in advance Gents.

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1 hour ago, peter wilson said:

PS does anyone out there know how much end float you should have on the rotating sleeve of the MU - un installed and push/pull on the drive end - I am getting quite a few mm yet cannot see how this is normally controlled. Ok normally the metering end is pushing back but that doesn't seem a satisfactory result. Thanks in advance Gents.

Hmmm. I understand the question but I'm not sure why you're worried. It's a few years since I pulled one apart, but I think the rotor is held by fuel pressure against a retainer plate at the end where the plastic dog engages. If I'm correct, it can't go the other way, so there's no end-float to calculate, only alignment with the sleeve openings. If that's wrong, you have problems best described by that well-known Hi-Lux ad (antipodean reference only).

BTW do you have a copy of the Lucas manual for the PI unit?

John

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2 hours ago, peter wilson said:

Hello Matt, I am also in AKL/Whangarei NZ with a TR6 with MU problems so may be able to help. Firstly are you in the NZ TR Register as the Technical chap Ken is absolutely brilliant at helping and very experienced (with around 6 TRs of his own to maintain), so can I suggest you contact him for help locally. secondly and after Kens help with my two MU's active plus spare, I believe that these should be setup by the OH facility which perforce must have a test bench for that task, and after this the unit should only require installation, timing to the engine and no other adjustments should be needed. This assumes an engine pulling good vacuum which mine wasn't.  As you found with the screws leaking (mine did likewise) these cars a a bugger if the vacuum is not there as they go to full rich and quickly wet plugs - lose ignition and its all over really. I have a permanently installed vacuum gauge now, and after head overhaul with new valves guides rockers shaft etc I now have good vacuum close to 9in Hg. The other problem area in my experience is the 6 butterflies and multiple linkages making it very hard to set up. I am looking to install an improved mechanism in due course.  Let me know prmwilsonatgmaildotcom if I can help locally.  Cheers Peter   JohnC thanks very much for the link to Peter Bower - I now have someone to send my MUs. Great.

 

PS does anyone out there know how much end float you should have on the rotating sleeve of the MU - un installed and push/pull on the drive end - I am getting quite a few mm yet cannot see how this is normally controlled. Ok normally the metering end is pushing back but that doesn't seem a satisfactory result. Thanks in advance Gents.

Welcome to the forum. Vitessesteve has the manuals John is talking about here:

http://vitessesteve.co.uk/LucasStuff/Lucas_Petrol_Injection_Manuals.htm

If you haven't already got copies.

 

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Hello JohnC and MikeC, Many thanks for your input. Yes I have those manuals and have pored over them in the past year but is still seems a bit of a mystery the MU. I have separated my spare unit and find it has lots of end float and even with good or full vacuum pulling the rollers right up the ramp there is still considerable end float. This can result in the outlet port not aligning completely with the rotating sleeve port which you would think would be an issue, as well its hard to imagine why having the rotating sleeves moving considerably doesn't in some way effect the effective stroke of the metering variable end stop.. But this is all just for my understanding. My main problem is cylinder 2 packed it in while on a trip and is not pushing fuel through - with the motor running on 4 1/2 and cracking the line at the injector there is no fuel coming out. Tried a brand new banjo bolt and still no good. Injectors are overhauled ones within 3hrs of running.  No pulse on 2 or 5. What is it with those two cylinders that they are the ones that typically drop out??  My MU has been overhauled new seals o-rings etc. It is driving me crazy.  Any help gratefully accepted!! Cheers Peter

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Most of my injector problems have been with 2 and 5, maybe it's because 2 and 5 have check valves built into the banjo bolts that leak or break up?

I  prime  my injectors by holding them with the line grading up ,spark  plugs out , "choke" full , on then bleed each of  them into a jar until  I see a good spray pattern- you might need to pull the tips with your fingernails to get this. I have a suspicion that if any air is left in an injector line the fuel from the MU pulses against the air without actually clearing it from the line.

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Hi Peter,

I've gone back to my spare unit and the PI Manual, and I wonder if your unit is missing something? At the distributor drive end the rotor should have a retaining plate (item no. 58 in Fig 18 in the manual), and at the CU end there should be a thrust plate (item no. 51). Each is secured to the rotor by two small screws, and they trap the sleeve between them, effectively limiting linear movement between sleeve and rotor. I can't see how you could get misalignment if both ends of the sleeve are constrained in this way. Worth checking?

John

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Hello John,

I have those gross controls over the end float in place yet there is still significant 0.7mm float. I have done a short video showing this. Of course I might be chasing my tail here. I agree that the fuel pressure must have some effect, yet so must the skew gear drive. All in all I expect this moves around significantly in operation. Mainly although I am worried about port alignment its more the effect on the metering - I cant help feeling this has to be affected by this linear movement. The shuttle wont know the difference between the end stop being moved by the metering mechanism ramp and rollers etc, or by the whole rotating sleeves moving due to this end float. I am sorely tempted to shim this to get say 10thou or so maximum. Here is the video link:

Cheers Peter Wilson

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And Mike yes I believe you are absolutely correct that any air then just absorbs the pulse like an air damper and the injector doesn't fire in that it need a good 55psi to break open. But that doesn't explain why I get no flow from the line when I crack it with the engine running on whatever other cylinders decide they want to.?? 

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One last quandrary - normally the various official Triumph publications state MU timing to be opening up  with a full hole being allowable. Eg this is from  the Fault Cards.

image.png.8c41c356cbb7bbd0ee6e2100e6cc2cbb.png

 

My latest installation gave me completely open hole (cyl 6) at TDC which I had been taking as allowable (Above bottom left situation). Now in the latest info the blue book there is conflicting information.

Petrol Injection System Fault Diagnosis.  image.png.2737597cbdaf850375d73dba09d23106.png

 

Which document would you trust on this??  Cheers Peter

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