Lotus Elan

3000rpm hunting

PostPost by: vstibbard » Sat Jul 15, 2017 8:57 am

Any suggestions the Elan has 1594cc 11.6:1 with new 45DCOE152 Webers, running 34m chokes, and tuned on the dyno, making ~155bhp on BP's Ultimate 98 octane fuel. The car is road registered an used for track days. Running on highway at part throttle 3000rpm with carb's right at the idle to main transition it starts to hunt/slight flat spot.

Overall the dyno tuning was to ensure it was safe for track use and not leaning out excessively, detonating etc, mixtures are spot on under those conditions, it idles at 800rpm, pulls like a train, and you can crack the throttles from off idle with no hesitation.

I can't details of what Lotus did to resolve a similar issue on the S4/Sprints when fitted with DCOE31's and the 33mm chokes, I'd like to try a similar approach to resolve the issue as first step Does any one know what the changes were?

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PostPost by: miked » Sun Jul 23, 2017 8:20 am

Hi Vaughan, It was to go down to 30mm chokes and 200 air correctors according to Miles Wilkins book. With loss of top end power.
I went from 31's to 151' s on a Sprint spec due to balance problems. With all the same jets etc swapped over I had the biggest stumble imaginable in the same area. So bad I thought it was electrical. I changed idle jets to richen and in the end reduced chokes sizes to 30 to cure it.
Others will know more but there is a difference in 151 and 152 carbs versus the original. Maybe due to position and number of progression holes. I believe reduced chokes size increases air velocity to pull more idle circuit fuel. I suppose you won't want to be losing top end so won't want to reduce chokes sizes. Looks like it will be idle jets mods. As I say, don't know much so others will give more detail.
Mike :(

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PostPost by: vstibbard » Sat Jul 29, 2017 10:23 pm

Hi Mike,

Thanks for sharing your experience, as the the new owner seems to be using the car on road more than track, reducing choke size would be the right direction, maybe even back to 40's for the 45's, either way it will get even more responsive down low.

I'll share the end result


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