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Dellorto Carbs Issues

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17 hours ago, Drawfiler said:

If it runs ok at lowbrevs, have you tried the car under load, it might just be possible it is runnig on two cylinders only, this will give you farts and bangs and lousy running under power.but will run ok at tickover speeds. I know this from experience! Check you have not swapped two leads over, you will get the right vac readings, perfect timing on no 1 and high HC readings.

Having had similar issues as above and changing everything from the battery to the plugs and doing all the possible combinations including stripping and cleaning the carbs, I found the best solution for me was to refit the rotor and trigger wheel several times until it fired consistently on 4 cylinders under load on the road. This did eventually stop all the misfiring banging etc. All is almost well and the only ongoing issue is the rev counter returning to tick over in 2 stages ,presumably a vac leak somewhere.......all suggestions welcome as to a cure.

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John, Have you checked that spark is actually going to each cylinder? If you put the timing light pickup on each lead  and it triggers then all good. I had a faulty magnetic trigger wheel in the distributor which caused the ignition module to not sense for two cylinders.

Also, have you done a static check that when the engine is in the position when ignition should happen(around 9deg BTDC) that the distributor rotor is in a position to actually line up with the metal conductor inside the distributor cap? If the distributor has been put back slightly off position it could work unreliably at best.

I also had serious spitting and stuff and timing was the issue.

Are you using the original Lumenition? Mine degraded significantly causing significant voltage losses. A new Powerspark/Accuspark unit worked fine, but did have a false start with aforementioned magnetic trigger.  

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Its the original Lumenition, I'm happy that its working as it should do. I have spent a fair bit of time on the phone to Steve their technical guy and he sent me the installation/testing and commissioning documentation for the systems when I first got the car, then spent some time later going through it, with me working on the car and him on the other end of the phone, also had a long chat to him Thursday afternoon regarding DWELL angle, the Éclat is 64.5 degrees and the Elite is 60.8 degrees. I did fit an Accuspark to my S1 elite which worked ok, so I will bear it in mind, rain has stopped play at the moment as I can't get the car out of the garage and my wife, Caroline has stopped me playing in the garage. Next plan is to do a voltage check between the two cars, as their both S2's and fitted with the same set up, I would expect them to be more or less identical.

CO for the Éclat is 2.16% and HC 1280ppm, which the mot tester has passed in the past. The Elite is CO 7.72% and HC 1810ppm


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If your happy that you have no vacuum leaks, your ignition wires are all measuring correcty, and that the dizzy cap and rotor arm are fine, try this one from leftfield:

try richening it up a bit. Although this sounds stupid for countering a high HC score, if you've gone too lean on a cylinder, it wont catch at idle, resulting in unburnt mixture going down the exhaust.


Also, check that the choke is returning properly.


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Might be worth just checking your cam timing as it's poss that the belt can jump a tooth or two when the engine backfires. only on the square tooth belt though. It did happen to mine so now have the later round tooth belt and wheels.

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On 17/07/2019 at 20:35, The Nut said:

These are out side the MOT limits, HC is excessively high, CO has been coming down as the mixture screws has been screwed in to bring down the rich mixture.  but car cuts out when the mixture gets too lean.

Any one got any suggestions on getting the HC down.

Regards to all John

This is why I prefer a Colortune to set the idle mixtures, it allows you to see what's happening in each cylinder as it's firing. :thumbup:


John W

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Hi to all, spitting and  backfiring solved.  a photo speaks a thousand words. these bits were found in the colortune which we used this afternoon. Ran the engine with no.2 plug out and had a black confetti shower,

I going to stand in the corner and hang my head in shame, still got high HC & CO but car running well. Work in progress as they say.



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Fwiw, another vote for the contrary step of richening the mixture.

my carbs (912 in an Esprit S3) were set at six and a half full turns out, and emissions were never a problem.....that said, last time it was tested was in '93 and running on four star.😳, and the exhaust routing is obviously different.

You could also make sure you're running on BP ultimate to clean it up.  A tree surgeon friend was advised by Stihl to only use that quality of fuel after he started to feel ill from the fumes at the end of a days work, even though he's 50ft up in the open air and near the coast! It made a huge difference.

I'll be watching closely as I'm almost at the point of getting mine running consistently now...

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Hi to all, 

The plan now for the Elite  is to run some redex through the engine and then put in a  couple of gallons of premium petrol and see what it does, CO is currently 5.58 and HC 2500, LAMBDA 1.105, this after using the color tune to set the mixtures

The Éclat is running at  CO 2.16 and HC 1320,  LAMBDA 1.282, as they the same engine and carbs, going to use this as bench mark to aim for.

Watch this space, John


I didn't answer your question, it looks like the remains of some blue paper towel I used to put in the inlets when I took off the inlet manifold, it was to stop getting bits of dirt in the cylinders.  You can see it in one of the earlier posts.


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