Lotus Elan

DCOE 18 vs 27

PostPost by: donselan » Fri Oct 11, 2019 9:17 pm

While trying to tune my carbs I have just noticed after 3 years of ownership that I have different carbs mounted on 45/6646. The rear is a 40DCOE18 while the front is a 40DCOE27.

What is the difference? Does it represent different stock jetting?

Until recently the car ran well so I am only now trying to improve the tuning. I am wondering if during a rebuild the previous owner installed the 27 because that was what he could lay his hands on. Hopefully he re-jetted the carbs to match.

Any suggestions?
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PostPost by: el-saturn » Fri Oct 11, 2019 9:29 pm

both should either be 18s (early) or 31s - your 27 is wrong and new jets won't get you where you wanna be - sandy
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PostPost by: donselan » Fri Oct 11, 2019 9:41 pm

Thanks Sandy,
I realize they should be matched but what is the difference? Is it a physical difference? Why only 18s or 31s? What is different about a 27 that makes it unsuitable for the Elan?
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PostPost by: Craven » Sat Oct 12, 2019 12:02 am

Usually it’s the size and position of the progression holes that is difference between early numbered bodies type . I know 28’s are Alfa’s so probably a 27 is, 18 & 31are original Lotus fitment.
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PostPost by: prezoom » Sat Oct 12, 2019 2:39 am

I am currently running 24's on my S2. Have sets of 18's and 31's, but the progression hole placement on the 24's seems to make for a better transition from the idle jets to the main jets, with less of a bog. The 152G (5 progression holes) carbs on the Zetec Plus2, work without any hesitation or bog. Keith's first gen VF tubes added a significant amount of poke over the original E tubes with the jetting I had worked out for the standard E tubes. Just installed his second gen VF tubes in the Elan, so Saturday will be the first real test of those tubes.
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PostPost by: oldchieft » Sat Oct 12, 2019 7:41 am

it could be the cover was damaged and swopped for a spare and the bodies are as built.

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PostPost by: nmauduit » Sat Oct 12, 2019 8:09 am

prezoom wrote:I am currently running 24's on my S2. Have sets of 18's and 31's, but the progression hole placement on the 24's seems to make for a better transition from the idle jets to the main jets, with less of a bog. The 152G (5 progression holes) carbs on the Zetec Plus2, work without any hesitation or bog. Keith's first gen VF tubes added a significant amount of poke over the original E tubes with the jetting I had worked out for the standard E tubes. Just installed his second gen VF tubes in the Elan, so Saturday will be the first real test of those tubes.


At the end of a dyno session I've had a go at a set of later tubes from KF (AB tubes #4 he selected based on the description of the build) I had purchased this the summer, with the best settings I eventually retained for the engine (idle 40F8 main 135 air 180) and the outcome was lower by at least 5hp on the whole curve from 2000 on with respect to E16 emulsion tube, so did not push further.

I'd be interested in the outcome of your tests...
Last edited by nmauduit on Sat Oct 12, 2019 12:40 pm, edited 1 time in total.
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PostPost by: Grizzly » Sat Oct 12, 2019 9:34 am

As Jon suggests it's likely the top cover just got changed as it's quite common for the float pivot to break.

As already suggested check the progression holes are the same size / position, things like the breather hole is present in the front of the main body casting and of course the jet sizes are the same.
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PostPost by: donselan » Sun Oct 13, 2019 6:24 pm

Thanks for all of the explanations and suggestions. I think it will be a winter project to compare progression holes size and position between the two carbs. I would love it if it turned out that they are the same and that it is only a replacement top cover.

Thanks again.
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PostPost by: cabc26b » Mon Oct 14, 2019 12:31 am

The 27's were used on 1600 cc alfa's - beyond the progression holes look at the accelerator pump - stroke differences can exist and also the 27's dont run the same pump jets as the 18 -
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PostPost by: types26/36 » Mon Oct 14, 2019 3:54 pm

Original specs for Alfa's with DCOE 27's.
And the pump strokes.
Attachments
pump-stroke.jpg and
33-002-copy.jpg and
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PostPost by: donselan » Wed Oct 16, 2019 11:52 am

Thanks for the great information. Now I have something specific to check.

Proof again that this is a great forum.

Thanks,
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