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Brandt

Misfiring Turbo engine

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Check the true diameter of the slow running jets. They can block up with varnish from evaporated petrol..then you have your lean mixture up to the point where the main jets kick in. I had just such a misfire and finally cured it by cleaning out the slow running jets with a piece of calibrated guitar string, of exactly the correct o.d. as the jets intended i.d. Before that,I'd tried everything, ignition, timing, carburetter adjustment, balancing, the works. After, it all came together, balancing was simple and all the misfiring had gone..it had misfired between 3000 and 4000rpm..just where you sit at legal motorway cruise, which was an infernal nuisance...but the misfire did clear if you gave it a bootful of throttle/accelerator pump/main jet. Definitely worth a check..if it's the same as mine, you cannot clear the jets by compressed air blast or any of the solvents I tried. Needed to be physically cleaned out.

Spitting back through the carbs. is definitely a sign of weak mixture..given that the ignition timing is not overly advanced. The needle jets probably won't affect the slow running, if they are too small then you might get too little fuel in the float chamber to sustain high RPM.

Edited by molemot

Scientists investigate that which already is; Engineers create that which has never been." - Albert Einstein

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Brandt

I dont think the needle jets will be your problem, although its probably better to have them stock.

There is only one carb adjustment for the lower revs range - The mixture screws. I assume you, or your dyno man have tried adjusting these (anti clockwise to enrich)? As you say, spitting back through the carbs suggests you are running weak. Do you know you idle CO2? The book suggests around 1% - but I need more like 2.5-3% to get it pulling nicely.

Apart from the 'gummy' jet theory suggested by John, its probably also worth checking float height, fuel pressure, the fuel regulator, although none of these would really explain why there is no fuel starvation at high revs.

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Hi Brandt

Just a thought, but are you sure that the carbs are for a turbo. The turbo carbs have a ball bearing that shuts off the pump curcit when on boost, also check the pressurisation of the fuel bowl, if there is a leak and the bowls are not pressurising uner boost this could lead to a lean condition. However i would not have thought that it would go rich at the top end if this was the case. Worth a check.

Andy

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I think it's time you bought The Book..."How to build and power tune Weber and Dellorto DCOE,DCO/SP and DHLA Carburetters" in the SpeedPro series, written by Des Hammill. It was this book that gave me the clue about the jets being reduced in size..as the jet sizes listed showed that the Lotus standard jets were right at the small end of those suitable for Esprit sized engines...so I thought it's a marginal deal, then, and any obstruction and you'll be way weak. Added to which, it's a good read with bags of information and some splendid colour illustrations which makes everything clear. Cost me twenty quid and worth every penny!!


Scientists investigate that which already is; Engineers create that which has never been." - Albert Einstein

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Sorry to hear about your problems Brandt. Will email you later today. What have you heard about the 87 HC any more news? Roger.

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Hi All

John, I've got Des Hamilton's book. Only wish it explained the actual operation of the carbs better, but at least the Lotus manual does that. I have found a nice link (http://www.sideways-technologies.co.uk/for...l?m-1201970113/) describing how to test the actual fuel level in the carbs, and that I will do tomorrow. I know it something small somewhere; but WHERE??

Roger, welcome back to Africa!

Kind regards

Brandt

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An interesting link, Brandt...my feeling about your problem is still the same..you have a restriction somewhere in the slow running system; either the jets are varnished up...use an old guitar string you've measured with a micrometer or digital vernier caliper as a gauge tool/reamer until you have the correct sized hole through the jet...or it could be the progression holes behind the butterfly which have got blocked...they were on mine; when I found that I thought I'd found the problem, but no...it took clearing the jets to the correct diameter to fix things. At least, once you've got it right, you'll know as much as anybody else about Dell'Ortos!!


Scientists investigate that which already is; Engineers create that which has never been." - Albert Einstein

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Hi Everyone

Well, it seems I've got the Lotus Esprit going :sofa:

Unfortunately I've changed a bunch of stuff in the same go, so I

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