Lotus Elan

Carbtune II connection to Webbers

PostPost by: Peter +2 » Sun Jan 07, 2018 10:07 pm

Will do.

Peter
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PostPost by: Esprit2 » Mon Jan 08, 2018 3:56 am

Only a rare few vintage DCOEs models (dash numbers) have vacuum ports for connecting manometers, as well as the Air Bleed Screws for balancing the two throats of a single carb. Yours don't. As others have noted, the current 40DCOE-151 and 45DCOE-152, as well as the similar DCOM have the vacuum ports.

Not to mess-up anyone else's plans for your Carbtune II, but I'd recommend that you hang onto it for a while. I've not tried either of these options yet, but I've been toying with the following ways to connect to my one 45DCOE-9 (I have lots of Dellortos that I really prefer, and just this one pesky DCOE that won't accept the Carbtune).

1) Use the Lotus OEM soft mounts with the thick, die cast spacer plate. Then drill a small (~ 0.5mm/ 0.020") dia thru-hole, vertically on the centerline. Follow that with a shallow hole (more of a counterbore) that's tapped M5 to accept the Carbtune's thread-in hose spigots... and later, M5 blanking screw plugs. You want the vacuum ports to be as close to the butterflies as possible, and short of drilling the carb body, the soft mount spacer plate is about as close as you can get.

1a) If the soft mount spacer plates are too thin for the required M5 hole size, then have a machine shop make up a set of thicker plates. They're not rocket science, and a little thicker won't mess-up anything.

1b) Make your own hose spigots with a smaller metric threads. Something that will safely fit into the width that's available on the soft mount spacer plate. I've made lots of 5mm spigots using 5mm thick-wall brass tubing. Cut to length (non-critical, but make those in a set close to equal), thread one end, and spin a nut on to form a shoulder/ stop. Slip a thin flat washer on, followed by a stretch-fit O-ring. The threaded end needs to be long enough to stick out past the O-ring far enough to thread into the port. So, do that, but start with a smaller diameter, thick-wall brass tube. No 'machining' required, just hand tools.

2) Drill & tap each manifold runner/ end flange to accept the M5 hose spigots... similar to the soft mount plate. It's further away from the butterflies, but not all that far. 2a & 2b as above.

For 1 & 2, make certain that the holes are perpendicular to the bores. Don't free-hand drill them... it would be best to pay a shop to do it 'right'. Since it's no simple task to take the Twink's intake manifold to the shop, the soft mount spacer plate becomes a more likely candidate.

3) Pick up a second set of brass screw-covers for the Progression Hole ports. Drill & tap them to accept the M5 hose spigots. I have less confidence in this one working as well as 1 & 2. At slow idle, only one of the progression holes will be exposed to the throat and full manifold vacuum. The other progression holes will be on the 'outside' of the butterflies, and exposed to near-atmospheric pressure... reduced, but 'near' atmospheric. I'm not sure what the end result vacuum is, and how strong of a signal it will give to the manometer, but that internal passage IS under a vacuum in order to work. If the weaker vacuum is adequate to work (?), it would be an easy, low part-risk way to go. When you're done balancing, replace them with the un-modified original plugs.

I wish I could report that these ideas work. But with only that one DCOE in my collection, I've been short on motivation to get the task done. It's been a "Round Tuit", and I've never gotten around to it.

If you make the effort to adapt the 4-tube Carbtune II to your carbs, I think you'll be glad you did. It really does make balancing the carbs 'easy'.

Regards,
Tim Engel
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PostPost by: Peter +2 » Mon Jan 08, 2018 10:56 pm

Tim,

Now thats thinking outside the box and I like your suggestion as the carbs are left untouched.

That's what I like about this forum people working together to solve a problem. I certainly am reluctant to admit defeat and you have got me thinking now what did I do with the OEM spacers as I have since changed to the more modern Masab variety.

I am reluctant to go back on my offer to Richard as a deal is a deal, but I will see if I kept my original spacers and if there is a enough material to follow your suggestion at some point in the future.

Many thanks

Peter
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PostPost by: richardcox_lotus » Tue Jan 09, 2018 10:12 am

Peter if you want to rethink that’s fine as I’m not in any hurry. I just thought if you wanted to move them on & want some cash then I could help out !

Too busy re-sealing cam cover at the moment....

Regards
Richard
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PostPost by: Peter +2 » Tue Jan 09, 2018 7:23 pm

Richard

Well in that case I might just hang on to them for a while just in case I follow Tims suggestion.

Good luck with the sealent and thanks.

Peter
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