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Two cautionary tales!


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I figure Id highlight a few things Ive found over the last few days to hopefully stop someone else having the same issues.

 

 

1) FACT:- a 0.75" rear brake seal DOES fit into a 0.7" rear cylinder. At least the kit I had did. Measuring the seals (both 0.75" and 0.7") are both identical, the only difference in the set I had was that the 0.75" has no recess/cavity behind the seal, where as the 0.7" seal does. Means the 0.7" seal can compress/retract further.

The net result for me was that I couldnt get the drum back on. The piston would not retract far enough for the shoes to retract sufficiently for the drum to fit.

I`ll see if I can get a few pics to illustrate better.

 

2) After replacing my brake master and servo, the car was running like a dog. Checking everything resulted in nothing untoward, until I checked the CO levels.

It would seem that the old servo was leaking (I suspect around the NRV as the servo diaphragm is good), and so letting in air.

I set the MU up with this leak (unknowingly) so when the leak no longer existed, the MU ran alot leaner.The engine was running alot hotter and the plugs were very glazed indicating a too lean mixture.

Worth considering if you change your servo, checking the CO as it could mean a premature end to your engine if it overheats.

 

Hope the above helps someone out!

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  • 1 month later...

Hi Andrew,

 

I was searching for "servo leaks" and found this thread:

 

What I don't understand is, when the MU was set up with an unknown leak, then it should run richer, after the leak is removed, as the additional amount of air sucked in by the engine is gone.

Or , am I misunderstanding sth.? (Unfortunately I have Webers, not (yet) injection.)

 

Thanks for clearing up.

 

Best Regards,

Patrick

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Patrick,

 

I wont admit to being an expert with MU's etc, but the higher the vacuum seen at the MU, the less fuel is delivered (highest vacuum is seen when throttle bodies are shut)

So with a (small) leak in my cars vacuum system, I set the new MU to deliver the correct (3.5%) CO at idle.

When the vacuum leak was fixed, this caused the vacuum to increase slightly, and therefore the MU delivered LESS fuel, making the engine run lean (plugs were white) across the total rev range.

A slight re-adjustment of the MU saw the idle CO go from <2.5% back up to ~3.5%.

 

Just remembered I had a good link in my bookmarks ..

 

http://t2000.kvaleberg.org/t_pi.html

 

scroll down to the TR6 PI cam tables. You can see the stages of vacuum vs fuel delivery.

 

Hope it makes sense.

 

Andrew

Edited by AndrewP
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Hi Andrew.

 

I have a co reading of 6.5 at tickover I would like to get it down to 3.5 and wondered how and what you adjust at the MU to bring the co level down.

 

I have done a fuel pressure test and got a reading of 7.3 bar at the MU I am not sure but I believe this equates to 105.85 psi at the conversion rate 1 bar =14.5 psi is this good or would you up it a bit.

 

Any information would be helpful. Regards John.

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Patrick,

 

I wont admit to being an expert with MU's etc, but the higher the vacuum seen at the MU, the less fuel is delivered (highest vacuum is seen when throttle bodies are shut)

So with a (small) leak in my cars vacuum system, I set the new MU to deliver the correct (3.5%) CO at idle.

When the vacuum leak was fixed, this caused the vacuum to increase slightly, and therefore the MU delivered LESS fuel, making the engine run lean (plugs were white) across the total rev range.

A slight re-adjustment of the MU saw the idle CO go from <2.5% back up to ~3.5%.

 

Just remembered I had a good link in my bookmarks ..

 

http://t2000.kvaleberg.org/t_pi.html

 

scroll down to the TR6 PI cam tables. You can see the stages of vacuum vs fuel delivery.

 

Hope it makes sense.

 

Andrew

 

 

 

Andrew,

 

thanks for your explanation. That makes perfect sense to me. The regulating impact of the vacuum on the MU is probably of higher impact, than the fact that you got rid of the air leak.

 

I was in deed trying to suck a vacuum into the servo, but the resistance stayed constant. I could suck for a minute and the resistance did not increase.

So I assume that I do as well have a (small) leak, or at the anti return valve or at the membrane.

Also, when I push the brake pedal with constant effort, while the engine is running and stop the engine, then I feel within 1-2 seconds how the servo effect goes away and the pedal pushes my foot back.

 

I think I'll better buy a new brake servo then.

 

Cheers,

Patrick

Edited by roulli
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John,

I think the recommended pressure is 108PSI with everything running (lights, heater etc). I`ll be honest..Im not sure how finitely critical the last few PSI are, so perhaps someone else can chime in.

Either way, your CO is high. Ive replied in another thread today with a few caveats and warnings so taking all those into account, if you want to simply adjust uniformly your fuel delivery across the whole range (i.e not changing the fuel 'curve') at all, then you need to do is to slacken locknut A1

Then move the whole shaft that the locknut was locking clockwise (I think) 1/4 of a turn. Make sure A2 and A3 all move together so as to adjust all together. Check the CO.

If you refer to the link above, 1/2 way down there is a nice pic of the MU and the control unit. You can see that by adjusting A1, you move, for a given vacuum (bottom axis) the fuel delivered (dotted line).

Perhaps an easier to understand diagram is here:-

 

http://www.lucasinjection.com/Lucas%20Mk2%20manual%20page%2024.htm

 

Anyway...as I said, do it slowly, check the CO and plugs regularly and its better to run slightly rich (not too much to wash the bores of their oil) than lean as things get hot pretty quickly. You do not want a plug breaking up and a loose electrode in the combustion chamber. Pistons + valve + debris = $$$$

 

Hope it helps

 

Andrew

Edited by AndrewP
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Hi Andrew.

Many thanks for your reply I have had the car 1971 cp checked again today the co readings were 6.77 at tickover and 10 at 2500rpm.

 

I looked at the Lucas diagram as you suggested and wondered if it is possible to do the adjustment with the MU still fitted to the car.

Would I have to undo the four screws and take the complete top off or could I undo the two screws and just take the coned part off.

Also would I need any gaskets etc.

 

The car starts very easily and runs smooth picks up straight away with no hesitation the exhaust smells a bit rich I wonder if I am being a bit picky and should stop worrying and just use it I would value yours and other members opinion.

 

Regards John.

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John,

 

It can all be done in situ, MU in car and running engine.

Just remove the black (or green sometimes?) cone to expose the adjusting rings. You will need to blank/block off the holes that the screws go into on the MU however as they go through into the vacuum chamber. Remember though...your not adjusting the lock ring, but the shaft the lock ring is holding in place.

The best thing Ive found with a CO meter is it gives you a definite value to always go back to. You say its 6.77% CO, so theres your starting and a value to go back to. Without the CO meter youd be guessing all the time.

Id say give it a go. If you do it slowly, going for a test drive each time, then you will be fine. Id aim for around 4-5% to begin with and see how it drives. Check the plugs as well for further confirmation that everything is happy internally.

For what its worth, another cheapish tool Ive found to be a worthwhile investment is an air flow meter. Again, gives you a visual check if the butterflies are all balanced and a figure to achieve on all 3 throttle bodies. Maybe not an issue on yours if its smooth however.

 

Cheers

Edited by AndrewP
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Hi Andrew.

Many thanks for your reply the plugs were a bit on the black side when I checked them. I bought one of those old crypton synchro meters on e-bay last night a friend of mine has one that we used to set the butterflies up on mine and his car found it to be very useful.

 

Regard John.

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Hi Andrew.

Many thanks for your help I followed your advice and adjusted the MU today I turned the shaft anti-clockwise a quarter of a turn at a time then checked the co levels.

 

I ended up turning it one complete turn and now have a co reading of 4.55 at tickover and 5.70 at 2500rpm.

 

Will take it out on a run next then check plug colour just need a dry weekend.

 

Thanks and regards John.

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