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Rich midrange on DHLA 40

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the car in question is a ´71 Lotus Europa with a modified Renault engine bored out to 1760ccm. The car just went back on the road with this engine. At the moment its running fairly rich. The Problem is that while revving the engine on a steady speed (3500 rpm and above) just maintaining speed i have a afr reading of 12.3-12.8. 

The car is fitted with early 40 Dhla(no letter, 3 progression holes)

Idle jet 45

Idle emulsion tube .2 

Main jet 126

emulsion tube .5

air correction 180

choke 33mm


I would say that the .5 emulsion tube is to big(it came with the carbs). I´ve searched a lot over the last few weeks, but i just dont know how big the difference would be with .6 emulsion tubes. The idle circuit is good apart from a too rich emulsion tube, a 40 idle jet was too lean.  


Thank you for your help

Greetings from Germany


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I have a copy of this book. If i go by the book i would need a .6 emulsion tube. The only thing that i have noticed is that a Alpine A110 1600(similar engine just smaller capacity) uses a .5 emulsion tube even though it doesn't suit the capacity of the engine.  

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When testing the 40 idle jets i had a different adjustment for the mixture screws. The change was next to nothing. I´ve done a bit more testing. Going off throttle at about 4000 rpm the afr reading is still 13.8. Going off throttle at even higher rpm the engine goes lean as you would expect(afr shows about 16) but going richer when falling below 4500 rpm. To me it looks like the main jet is to big. I will do some more testing with different mixture screw settings

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  • 3 months later...

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