Lotus Elan

Webber Trumpets

PostPost by: carrierdave » Sun Sep 11, 2005 8:09 pm

Good evening,
When I first took my Webbers apart there was a reddish brown mastic around the trumpets. Obviously I cleaned it off and put the carbs back together without anything - As you do!!
The question is do I need to use any form of gasketing material such as RTV? The reason I ask is that today I took them off to clean and there was this green sticky residue which I can only presume to be evaporated petrol/oil.

Any comments and suggestions would be appreciated.

Thanks

David
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PostPost by: berni29 » Sun Sep 11, 2005 10:28 pm

Hi Dave

I have never come across sealant on the trumpets themselves, but before the backplate goes on I put a smear of silicone sealant on the carbs around each throat. I don't think that it would be worth doing to the actual trumpet as they are a pretty close fit and the only air that can get in is via the airbox (assuming a sealed backplate). That’s my opinion anyway!

All the best
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PostPost by: marcfuller » Mon Sep 12, 2005 3:11 am

I have an Elan manual (Brooklands- Lotus Elan Owners Workshop Manual) which states as follows on page 36-

"Weber carburetter air trumpets :
Commencing at engine No C22414, the trumpets are sealed with Hylomar SQ.32M compound. This precludes all unfiltered air from leaking into the carburetters. This sealing may be applied to earlier engines. Apply the Hylomar compound round the inner faces of the trumpet shoulders, fill the mating recesses in the carburetter air inlets with Hylomar compound, leave for 10 minutes to allow the compound to partially set and assemble the trumpets and air box to the carburetters."

Keith (type26owner) has found that gas (petrol) will also leak from the base of the trumpets at rest, causeing a hazard and smell. I believe he uses some gaskets he made up to resolve the issue rather than use sealant. Keith wrote extensively of this problem in some posting a few months ago on this bbs if you want to search.
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PostPost by: carrierdave » Mon Sep 12, 2005 9:40 pm

Thanks for the replies - I will take a look on the web and see if I can find the Hylomar compound you refer too.

Regards

David

PS Berni - Love the web site. Always look forward to your updates.
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PostPost by: berni29 » Tue Sep 13, 2005 2:09 am

Hi Dave

Thanks for the compliment. I have some more stuff to put up and will do that soon. I am going to seal my trumpets as well. One in particular (the back one) does get a bit wet.

All the best....
Racing green +2s with green tints. See it at:

www.searchsmart.co.uk/lotus
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PostPost by: type26owner » Tue Sep 13, 2005 5:27 pm

Might add that there are major differences between the air trumpets and auxiliary venturis used by Weber. The 31s have air trumpets that mount flush to the carb body without the tube extension that sticks down over the auxiliary venturi clamping it into position. Instead the flat ended trumpet contacts the upstream face end of the auxiliary venturi which has the same OD it's whole length. A flat thin (~1/64") rubber gasket ought to seal that combination up air and fuel tight.
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PostPost by: rgh0 » Wed Sep 14, 2005 11:07 am

Keith

I dont know about all 40DCOE31's but the ones that originally came on my 68 Elan, serial numbers 9521 and 9533 came with the trumpets that extended down the bores and overlapped with the auxillary venturies.

Rohan
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PostPost by: type26owner » Wed Sep 14, 2005 1:55 pm

Rohan,
That's interesting. Is it possible that these air trumpets and auxiliary venturis components are Dellorto ones that someone kludged together into the Weber carburetor body?

Reread John Passini's Weber combined works book last week and have concluded I'm at odds with some major observations and tuning principles he's stated. Additionally most of his technical comments made directly about the Elan I was not able to understand at all. He became quite obtuse with his choice of wording so much so I totally missed the point he was trying to make! :?
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PostPost by: carrierdave » Wed Sep 14, 2005 3:50 pm

Hi Keith & Rohan,
My car is a 1969 built +2s equipped with 40DCOE 31's; serial numbers “14826 & 15559” all confirmed by Lotus.
They certainly have the collar that extends down into the bores of the carburettors; as too whether or not these trumpets are standard Lotus/Webber supply I cannot say.

I have just checked a Haynes Webber Carburettor book I have that dates back 15 to 20 years ago. It shows an exploded view of the 38 – 48DCOE and clearly shows the trumpet with its collar stop and extended section that fits into the bore.

If you want to have a look I will either take a photo or try and scan it in some time.

Regards

David
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PostPost by: type26owner » Wed Sep 14, 2005 8:53 pm

As far as I can tell the auxiliary venturi and air trumpet I mentioned before are in fact old style DHLA Dellorto components which got installed in a Weber DCOE_31. The auxiliary venturi had the identical P-shaped retaining spring female pocket as the Weber one and that kinda baffled me (why would anyone copy that horrible design?). The exploded view of the DHLA shown here is shows the parts except these are held in with a grubscrew. This is the air trumpet though with a flange to secure it to the carb body. Sorry for adding to the confusion here but this helped me sort some of Jon Rosner's carbie woes. :) Click on the tiny picture to get an enlarged one.
http://www.lotuselan.net/publish/lpb_dellorto_carbs.shtml

Thanks Rohan and David. I never would have solved this problem without your feedback! This is exactly the stuff where my inexperience will hinder me.
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PostPost by: twincamman » Wed Sep 14, 2005 10:05 pm

I suspect someone has substituted Webbers from an alpha on your motor ----mine on the elan were from 1750 and have the bolt on velocity tubes ---the 7 has lotus carbs and has the slip in tubes -both sets are 40 doce -- ed
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