Lotus Elan

Dellorto Choke Size

PostPost by: William2 » Thu Jun 15, 2017 10:40 am

For an SE spec engine there appear to be two different choke sizes listed for Dellorto carbs, 30 and 32mm. Can anyone confirm which size is best?
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PostPost by: rgh0 » Thu Jun 15, 2017 10:52 am

Dellortos were never standard factory fitment to SE engines as far as I am aware as by the time they were introduced all engines were Sprint specification. However 32mm chokes were standard on Weber SE engines and I would start with that if I had an SE engine with Dellorto carbs. 30mm chokes were used on standard B cam 105hp engines, though there appear to be some Lotus recommendations to try 30mm chokes in SE engines to help solve problems. I have never understood or researched this as 32 mm chokes work well on most SE engines I have seen when tuned properly. I presume at some stage Lotus generated settings for 30 and 32 mm choke Dellortos when they move to these in the early 70's to provide a reference to earlier owners who moved their car to Dellortos which I presume was the dealer supplied replacement part at the time for earlier cars with Weber carb problems

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PostPost by: nigelrbfurness » Mon Jun 19, 2017 8:34 am

The original 32mm choke setting on the first Weber S/E engines caused some engines to stumble (flat spot) slightly around 1700-2000 rpm. This became worse as the engines got a few miles on them. The original settings for the Dellortos on the 907 engines when fitted to the Jensen Healey (first application) also showed this problem. Both were solved, with some slight loss of top-end BHP, by reducing the choke size. On the 907, some other jet changes were needed too. It seems to be a problem when moving from the slow-running jets onto the main jets and a careful or knowledgeable driver could probably drive through the flat-spot successfully. However, the choke reduction was a factory recommended change which I remember applying to several cars with complete success in terms of improving everyday driveability. Likewise with the JH.

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1970 S4SE/1760cc big valve/SA-AX block, L2s, 45DCOEs, 1978 Jensen GT, 1962 AH Sprite, Alfa-Romeo 159, 1966 Bristol Bus, 1947 AEC Regal bus.
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