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Paul Coleman

Running lean

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I took my car back for its MOT after it failed on emissions (and steering) a couple of weeks ago. Initially the CO was 0.067% (very very low) and HC was 2857ppm.

 

So I used a colour tune and twiddled the mixture screws to get a blue flame and now I have CO=2.1% and HC=1067ppm which is a pass.

 

It still failed on the steering but that's another story.

 

My problem is that it's popping and the back box of the SJ stainless steel exhaust gets so hot you can't touch the rear valance. I rang SJ and they said it was too lean but the mixture screws are wound out a fair way on all carbs.

 

I took the exhaust off and resealed it as I'm pretty sure it was leaking between the manifold and the middle section. The carbs have been stripped, cleaned and rebuilt with a new rebuild kit.

 

Does anybody know what else I could check before my car melts?

 

Thanks, Paul.

Edited by Paul Coleman

Lotus Esprit [meaning] a 1:1 scale Airfix kit with a propensity to catch fire

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How close is the silencer to the valence?

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Very!

 

But it shouldn't be that hot in the first place.

Edited by Paul Coleman

Lotus Esprit [meaning] a 1:1 scale Airfix kit with a propensity to catch fire

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The CO is only just in the acceptable range for your car. (2-3% I think for your 907) I would aim for something nearer to 3% and see where that leaves you.  (Mine runs like s*** on anything less than 3.5 -4%)     

 

I am assuming your ignition timing is correct and you have the correct distributor fitted.  As suggested maybe your silencer is too near the valance?   I doubt your exhaust is as hot as a Turbo exhaust after a quick run  

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Take it to an expert. Cheaper than a rebuild with a new set of pistons.


'A pound of rubber is worth a Ton of engineering.'- Jim Endruweit quoting Colin Chapman.

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Hi Paul,

 

Have you carried out a compression test? I had a problem many years back with my ex turbo HC, it was popping like a trooper on overrun and it turned out to be the exhaust valves needing to be replaced. It still ran very well and the mechanic was amazed it ran at all.

 

cheers

 

-Chris

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I did do a cold compression testand got 160psi +/-2psi on all cylinders. I ran out of patience and ability in the end and it's now with SJ Sportscars waiting to be looked at...


Lotus Esprit [meaning] a 1:1 scale Airfix kit with a propensity to catch fire

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Chi-chink but a running esprit...


Something I learned about cars or planes, it all works until it doesn't anymore...sometime there is no way around it!

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Not quite!

 

It turns out that the head gasket is leaking in about 8 places. Steve reckons the liner nip is too high despite me having the engine rebuilt by an engine builders that have been in business for 40 years. I'm now looking at a bill for the best part of £2,000 to get SJ to fix the problem or the alternative is to pull the engine myself and take it back to the people I paid to rebuild it. Neither option appeals!

 

My original problem of back firing seems to have been caused by distributors. My original was worn so I bought a new one but the curve is completely wrong according to SJ (even though I gave them the figures and asked if they could match it). It has 25 degrees of advance between idle and max revs when it should only have 16.

Edited by Paul Coleman

Lotus Esprit [meaning] a 1:1 scale Airfix kit with a propensity to catch fire

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Feel for your frustrations. Very difficult to find someone you can trust with these engines outside the Lotus circle.

Though, admittedly, it's not exactly rocket science is it?


'A pound of rubber is worth a Ton of engineering.'- Jim Endruweit quoting Colin Chapman.

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Sorry about your problems. Out of interest did they fit new liners or move them around when rebuilding the engine. If they kept the same orientation then the clamping pressure from the cylinder head should seat them properly. But, why would a leaky head gasket cause overheating of the exhaust box??

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Virtually everything in the engine is new.

 

The head gasket leak didn't cause the backfiring and hot exhaust, that was caused by worn and faulty distributors (both new and old).


Lotus Esprit [meaning] a 1:1 scale Airfix kit with a propensity to catch fire

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How does SJs know that the gasket is leaking in about 8 places. Have there been telltale signs such as large amounts of steam coming from exhaust, mayo under oil filler cap or water getting into oil.  

If the dizzy problem has been fixed I would be inclined to run it a while before throwing £2k at it.

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There were traces of coolant on the engine and I wasn't sure where it was coming from. The MOT tester picked it up as a leak. I'm not going to have SJ do it. I'll drop the engine if necessary and return it to the engine builders who did it for me.

Edited by Paul Coleman

Lotus Esprit [meaning] a 1:1 scale Airfix kit with a propensity to catch fire

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OK so head gasket has gone. Dont blame you not paying out another £2k to get it fixed - might not be the liners that are out. You could take the head off without removing the engine just to verify that nip is out. As Scott says if they skimmed the head and didnt do a proper job then that could be the problem. Also an incorrect head gasket. 

If you simply return the whole lot to the original rebuilders they are likely deny it was anything to do with them and say it was how you drove the car..

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Driving it any way you like won't make the head gasket go, I think your choice is the right one. I would want to be there when they open it and re-measure the nip. If they are half decent it shouldn't cost you an arm. But then again, all the work of bringing them the engine won't go away...

Just imagine getting somebody who knows what he's doing on this side of the pond...

Good luck.


Something I learned about cars or planes, it all works until it doesn't anymore...sometime there is no way around it!

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They did skim the head but it was virtually nothing and the head hadn't been skimmed before.

 

If I open it up to have a look and then take it back to the engine builders they will probably not want to know - which I can understand. So I'll probably take it to them and see what they say. If it's within the next three weeks I'll go with it as I'm off work until the 24th.

 

They are a reputable company and have been in the business over 40 years. The chap who built the engine for me has been doing it for 50 years.

 

All the spares including the head gasket came from SJ Sportscars. It had new pistons, shells, liners, valves, valve guides and all gaskets and belts.

Edited by Paul Coleman

Lotus Esprit [meaning] a 1:1 scale Airfix kit with a propensity to catch fire

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Paul

 

Really sorry to hear of these troubles. Im sure once you get the head off all will become clear. Hopefully it will be something simple.

 

Once sorted and you get your dizzy issue sorted you will be up and running.

 

Buddsy


 

"Belief is the enemy of knowing" - Crrow777

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Talking to Steve at SJ he said that although the workshop manual says the nip should be between 0.003" and 0.005" he usually aims for 0.002" and if it's 0.006" it will leak.


Lotus Esprit [meaning] a 1:1 scale Airfix kit with a propensity to catch fire

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Dear Coleman,

 

I did not answer until now, because I think I have not enough Information about the Situation but

I would not blame anyone but maybe we Germans make the diagnostic be bit more straight forward.

 

So:

 

First question: was the popping at and before your first visit for MOT?

It is not the first time I use different Setups for MOT (TÜV) and driving.

 

Is the popping at iddle only or at higher revs under load also?

 

Color Tune is one thing but what about the vacuum balance and amount of air flow for each cylinder?

 

If you have Color Tune what does it look like while popping appears?

(If you can manage to balance vacuum and firing perfect you should not worry any more about Head Gasket and liners and so on.

If not it will start another Task)

 

You worked on the gasket for the exhaust - Keep more an eye on the sealing on the path from the carbs to cylinder head.

 

And again Keep cool - with your compression values it should be possible to overcome the problem without pumping to much money to experts.

 

But think about - every Esprit which burns down raises the value of the remaining!

 

regards

 

Mad_Wolf

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Dear Coleman,

 

 

reading your popping and hot exhaust I have got several answers.

But why 2 topic's?

 

 

 

So you have balanced your carbs and you had the popping before - right?

Left is the question at which condition the popping appears and what the Color Tunes Shows at this point.

 

If you have the feeling that the exhaust system itself makes the problem take it complete of - make a heat sheald and let the Motor run.

If the flames are all the same on the 4 cylinders you might be right.

 

 

 

regards

 

Mad_Wolf

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