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Paul Coleman

Unable to setup Dellortos on an S1

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I've been trying to setup the Dellorto carbs on my S1 for longer than I care to remember and I've got them somewhere near but something's not right.

 

I've used a colour tune and Carbtune 4 channel manometer. The timing is set to 8 degrees BTDC as per the manual.

 

It ticks over at around 950rpm on the dash gauge and the timing looks pretty solid. However, it pops occasionally on some of the cylinders whilst ticking over and when I rev it the popping gets more frequent and also occurs when I release the throttle. You can see white flashes through the colour tune when it pops.

 

The carbs have been balanced using the manometer and they're pretty close showing about 40% deflection of the rods.

 

I'm running out of patience with this thing and earlier this week I took it for an MOT which it failed miserably on emissions. The CO was 0.067% (max=4.5%) and the HC was 2875ppm (max=1200ppm). However, when I put the colour tune on it some of the cylinders were nowhere near a nice bunsen burner blue flame.

 

The engine has been rebuilt by an engine builders and has new everything virtually.

 

Has anybody had any similar experiences?

 

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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I assume all your jets are as per the manual?  As you note, your CO is incredibly low - I'm suprised it runs.  Also if its sort of 'coughing/spitting back at the carbs,, that's another indication you are simply running too weak - resulting in misfiring and unburnt fuel (high HC).  I would be looking to open the mixture screws....   Ideally you need to persuade your local garage to use an analyser as you adjust.  

 

NB - I think your colourtune will be all over the place until you get close, 

Edited by 910Esprit

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All the jets are as stated in the workshop manual - I checked them all the 4th time I pulled them apart to clean them!

 

I fitted a new rebuild kit and put over 100psi through all the passage ways when I had them apart.

 

I had tried setting them using just the carbtune manometer and had managed to get 40% deflection on all rods and had balanced them using the air bypass screws and the carb to carb balance linkage. I then took it to the MOT and got the readings I stated previously. However, when I put the colour tune on it yesterday a couple of the cylinders were sparking but I couldn't see any kind of flame in there so I'm assuming those cylinders were so far out it was dumping unburnt fuel straight out of the exhaust, hence the high HC reading.

 

I don't have any real experience of doing this so it's all new and I'm learning as I go. Yesterday I managed to get a bunsen burner blue flame on all cylinders but I do get the occasional popping at tickover and when I rev it.

 

At tickover it feels like the engine wants to rev more but something's kind of holding it back?


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

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What about the float levels & the mounting O rings, are they correct, in good condition & correctly fitted?

 

When you rebuilt the carbs did you fit new spindle bearings, at high mileages they can wear & randomly leak air?


Cheers,

John W

http://jonwatkins.co.uk

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40% deflection means nothing really - you are looking for the same deflection across all 4 cylinders - Use a vacuum gauge if you want to check the vacuum at idle.   I'm assuming that your valve timing is correct and the ignition components are in good condition.   I still think you need to get your CO normalised before you worry about the HC.   Its either that low because you have the mixture screws pretty much screwed in, there is a blockage in your idle circuits or some other issue that's stopping fuel flowing

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Virtually everything is new and yes I did replace the bearings on the throttle spindles.

 

I've been using a 4 channel manometer (Carbtune) to balance them and they're pretty good - even if I do say so myself ;)

 

Just the popping that I need to get rid of. I will try to richen the mixture a bit more and see if that helps.


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

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