Lotus Elan

Weber jetting

PostPost by: seniorchristo » Fri Nov 03, 2017 4:18 pm

Keith Franck has been studying, experimenting, and modifying Weber carbs, particularly the DCOE variety for at least 15 years. He runs a forum called sidedraft central
https://groups.yahoo.com/neo/groups/sid ... ntral/info
The website is somewhat disjointed but there is a lot of good info there.

He has designed and manufactured a number of jet and emulsion tube replacements which some Elan.net members have purchased and used with success.

Keith has just recently developed a VF tube (Venturi Fountain main circuit tube) which along with a spacer, is a direct replacement for the existing emulsion tube. Keith has used these tubes in his basically stock S2 Elan and reports the performance results are amazing with the performance gains especially noticeable at full power. My interest in improving carb performance is mostly to eliminate off idle/transition flat spot stumble but these tubes look like a win/win possibility. Has anyone here been following these developments?
Chris :)
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PostPost by: Hawksfield » Fri Nov 03, 2017 4:49 pm

Hi

I have set up my float levels using the Keith Franck method what a difference it made
Then set balance with 4 way balancer
See his tuning sheet


Weber_DCOE_Tuning_White_Paper.pdf
(96.98 KiB) Downloaded 684 times
Regards

John

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PostPost by: prezoom » Sat Nov 04, 2017 12:01 am

I have been following his attempts at making the DCOEs perform better since 2006. Ken at Bean's put me on to his original white paper on setting float levels back then, which I did on the S2. Managed to retrieve all of his posts on this site before he started sidedraftcentral, and get all of the posts from that site today.

It always seems something better comes along, though, this time I think he may have hit the jackpot with the new tubes. Interestingly, when I installed the 152G's on the Zetec, and set the floats to the suggested 25mm, the car has absolutely no hesitation anywhere. With an aluminum flywheel, I would think any hesitation would be seriously amplified, so I am quite pleased with my low cost choice.

Without an Inovate or other measuring device, I cannot determine the nature of the fuel mixture on the Zetec. Have yet to do a decent mileage check, but it does not seem to be overly thirsty. I have a set of 24s that I would like to try modifying the progression holes to those like the 152Gs, and try on the S2 to see if it behaves like the Zetec. My 18s and 31s would not be touched.
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PostPost by: RichardHawkins » Sat Nov 04, 2017 6:36 pm

Chris,

Like you I have been following Keith's work for a few years, and hoping that he will produce a definitive solution, which he seems to have done with these VF tubes. Keith is a perfectionist, and keeps improving something that is already good. In a way I hope he is satisfied and can now find time to work on other features of his car. My car is a long term restoration project, and I oscillate between favouring fuel injection or Keith's alterations. Currently I favour Keith.

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PostPost by: Certified Lotus » Sat Nov 04, 2017 8:05 pm

Chris, greatly appreciate the research you have done on this. Will order a pair for my S1 to see if I can remove the ?stumble? at low rpm.
Glen
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PostPost by: seniorchristo » Sat Nov 04, 2017 9:56 pm

Hi Glen
I don't think these tubes are the definitive solution for low RPM stumble but they are probably a good starting point. Keith has other products which directly address the stumble/flat spot issue but they require considerable research to determine which size is appropriate to your particular engine. The more I study Weber carbs, the more I realize what a complex subject it is, even for the experts. Kudos to Keith for all his hard work. :)
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PostPost by: seniorchristo » Sat Nov 04, 2017 9:59 pm

Glen
You will need (4) tubes, two per carb. :)
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PostPost by: nigelrbfurness » Sun Nov 05, 2017 9:24 am

The float heights are critical in tuning out the low-end "stumble" mentioned in this thread. It took me some time - well a few hours - of careful adjustment but now my car drives perfectly smoothly from idle to mains just using standard weber jets and carefully adjusted float levels. If your carbs are correctly jetted as per the engine specs and you still have this problem, then examining the fuel level in the float chamber should be high on your list.

Nigel F.
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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PostPost by: Certified Lotus » Sun Nov 05, 2017 11:12 am

Thanks Chris and Nigel for the more detailed info. Guess I?m going to become intimate with my Weber carbs. Winter project along with the rebuild of my 72 Europa (which also has Weber?s).
Glen
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PostPost by: elancoupe » Sun Nov 05, 2017 11:21 am

Nigel is spot on, correct fuel level in the carb is VERY important. In conjunction with a recurve of my dizzy, proper fuel height made a massive improvement in my driveability.

Chris can attest to how well mine performs now :D :D
Mike
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PostPost by: Craven » Sun Nov 05, 2017 11:33 am

nigelrbfurness wrote:The float heights are critical in tuning out the low-end "stumble" mentioned in this thread. It took me some time - well a few hours - of careful adjustment but now my car drives perfectly smoothly from idle to mains just using standard weber jets and carefully adjusted float levels. If your carbs are correctly jetted as per the engine specs and you still have this problem, then examining the fuel level in the float chamber should be high on your list.

Nigel F.

Playing around with Webers over some 50 years, one of the best improvements I made to the earlier carb?s, 18?s 31?s era, was to use the later moulded plastic floats. This did need the height of the needle valve mounting reduced but the improvement in fuel level control was very beneficial in maintaining the extremely high level needed, without flooding.
BTW, Weber has over the years produced over 50, yes fifty, different emulsion tube designs for the DCOE carb.
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PostPost by: Chancer » Sun Nov 05, 2017 2:33 pm

One design but 50 different calibrations.

Keith's ones sound like a new design.

Spanish ones aside are their good and bad model numbers, are some more suitable for certain engines? Why do people insist on the "correct" carb numbers for the twin-cam engine? If they have the same chokes, jets, emulsion tubes etc is ther really any difference? - progression hole drillings perhaps?

I am back in the UK at the moment and trying to reclaim my garage after more than a decade, I came across 3 sets of DCOE carbs, will post the model numbers later, I would like to know where they originated and what if any engine they are best suited to.
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PostPost by: seniorchristo » Sun Nov 05, 2017 2:38 pm

elancoupe wrote:Chris can attest to how well mine performs now

Mike
Yes I can!. Perhaps I'll race you over to Cleveland next summer! :)
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PostPost by: prezoom » Sun Nov 05, 2017 5:06 pm

In looking at my 18s, 24s, and 31s, they each have different pattern of progression holes, though each have three.
Rob Walker
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1964 Elva Mk4T Coupe (awaiting restoration)
1965 Ford Falcon Ranchero, 302,AOD,9",rack and pinion,disc,etc,etc,etc
1954 Nash Healey LeMans Coupe

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PostPost by: Craven » Sun Nov 05, 2017 5:56 pm

prezoom wrote:In looking at my 18s, 24s, and 31s, they each have different pattern of progression holes, though each have three.

Not only does the pattern change, this give different throttle plate angles at each hole, the progression hole diameter itself is also varied.
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