Lotus Elan

Weber carb rebuild

PostPost by: dunclentdr » Sat Aug 09, 2014 11:16 am

I have recently acquired an early ('67) Plus 2 that has been running very poorly.

Aldon inspected the carbs and diagnosed a large air leak and have subsequently fitted a replacement pair of (new) Webers, the car now runs well.

Their advice was not to spend time and money on rebuilding the original carbs but I would now like to investigate how to do that.

Does anyone have advice on whether it should be possible to fully rebuild the original carbs and if so who would be best to do so?

Thanks

David
Last edited by dunclentdr on Sat Aug 09, 2014 12:37 pm, edited 1 time in total.
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PostPost by: billwill » Sat Aug 09, 2014 11:46 am

Can I suggest that you buy a copy of this book
http://www.ebay.co.uk/itm/like/37076047 ... 108&ff19=0

It will enable you to decide if the job is worth doing and whether or not to do the job yourself. You can buy parts from Q.E.D or Burton Motorsport, but a whole body might not be available new.
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PostPost by: bill308 » Sat Aug 09, 2014 8:43 pm

Hi David.

Did Aldon indicate the source of the air leak?

Possibilities include:

Leakage past the throttle shaft bearings - new sealed bearings or renewing the leather seals may be possible
Warped base leakage do to over tightening - it is possible to machine the base flat
twisted throttle shaft - it could be replaced or carefully bent back into spec.

There may be other possibilities, but the above probably require the services of a specialist. Special Weber tools are no longer available to facilitate removal of the throttle shaft and drilling of a hole for the pump jet pin. The shaft seals may be repacked with grease, but I'm not sure how effective this is. A good machinist can mill the bottom flat, but perhaps some sealant might be all that is necessary.

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PostPost by: silverlink » Sat Aug 09, 2014 9:11 pm

Hi David,
Have just got my Webers back after total overhaul and they look totally stunning. They were sent to RPM at Market Weighton tel no 01430 872145 ask for Neil. Cost was around ?230 and for that he totally dismantled them ultrasonically cleaned them checked all the jets and moving parts replacing anything that needed to be. Finally the bodies were cleaned to look like new.
Give Neil a call he'll go over it all with you.
Cheers
Ian
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PostPost by: mbell » Sun Aug 10, 2014 9:39 pm

You should be able to rebuild them. For a garage they simply don't want to mess around them, rather bolt in a new set and get the car going. Can't blame them for that, it's a fiddly time consuming job.

Rebuild kits are pretty cheap and just takes time to strip them down clean everything and rebuild.

The weber that came on my car were missing all the jets/holders and had a few wasp nests (!!) in them. I've stripped them not knowing anything and got them up and running. Still need to balance them and fine tune them and took a a couple of goes but an interesting thing to do. Especially as no pressure with having working carbs on the car at the minute.
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PostPost by: Bob » Sun Sep 14, 2014 6:42 pm

Hi,
I am doing some research I need to clean up and rebuild my own 40 DCOE's on my S4 I found this on the web
https://www.youtube.com/watch?v=4dxO1TPWhlE
there are others in the series
Hope this helps.

What I need to do is clean them I cannot find anywhere that does small part hydro blasting, what i have thought about doing is using baking soda solution in a spray attachment to my power spray, anybody tried it?

Bob
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PostPost by: Galwaylotus » Tue Sep 16, 2014 1:00 pm

I rebuilt mine with no problems. It helps to have the Weber manual so that you understand what each circuit does. Float levels should be set per Keith Franck's method, more accurate than the factory method!
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PostPost by: bill308 » Thu Sep 18, 2014 12:45 am

Can you describe Keith's method for setting the float heights?

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PostPost by: mbell » Thu Sep 18, 2014 4:17 am

You set the fuel level to 25mm from the top of the main circuit jet holder. This is 2mm below the hole to the intake throat on the carb.

I use a pointed end mini screw driver and Mark it 25mm from the tip with tape .then slide this down the jet holder and watch for the shimmer of the fuel when it touches. From this you can see if the fuel level needs adjusting up or down and roughly how much.
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PostPost by: prezoom » Thu Sep 18, 2014 3:47 pm

Keith's original method was using a short section, between 2 and 3 inches, of an acrylic rod, with both ends polished. I believe he then used a bored out nylon nut that was a firm slip fit over the rod. The rod should be just small enough in diameter to fit down into the emulsion tube well, without dragging. Remove the emulsion tubes from the carb body. By resting the nut on the top of the flat surface where the emulsion tube is fitted, then slide the rod down until it contacts the fuel in the emulsion tube well. You can see the top of the rod darken when the rod just contacts the fuel. Remove the rod and nut from the well and measure the distance from the under side of the nut to the end of the rod. This measurement should be 25mm. Most hobby stores carry acrylic rod, or a shop that deals in plastics.

You also have to make sure that the fitting of the float to the retaining/pivot pin in the top of the carb is not loose or sloppy. Snug enough to allow free movement of the floats, but not so tight as to bind. For me, this has been the most effective method of setting the float level.

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PostPost by: KevJ+2 » Sat Sep 27, 2014 12:50 pm

After reading these replies and watching the very interesting Weber videos, I got distracted from other bodywork jobs and decided to strip down my 40-31s.
All seems do-able apart from (so far) an inspection cover brass screw being churned off :evil:
But my two questions (so far) are -
What can I do to remove the venturi plugs on the outside body. I can't find any information on these as they normally seem to be held in by screws and either wire or a double lock tab?
Also, is it best to change any jets due to possible wear or just clean, inspect and refit and use the service kits?
I'm really tempted to do this myself as it's not rocket science but needs to be right.
Regards,
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PostPost by: Galwaylotus » Sat Sep 27, 2014 2:04 pm

I just checked my jets. They didn't need cleaning but if yours do something like an ultrasonic bath should be used. Certainly avoid using any metal items on the bore. The Weber Tuning Manual (available from Webcon http://www.webcon.co.uk is invaluable for doing the rebuild. It gives an explanation of the various circuits and what each is for as well as helping with the settings. Fuel level in the float bowl should be set per Keith Franck's method as it's more accurate than the Weber method. Another good book is Des Hamill's "How to Build and Power Tune Weber and Dellorto Carburettors". Amazon carries this one.
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PostPost by: rgh0 » Sat Sep 27, 2014 11:14 pm

KevJ+2 wrote:What can I do to remove the venturi plugs on the outside body. I can't find any information on these as they normally seem to be held in by screws and either wire or a double lock tab?
Also, is it best to change any jets due to possible wear or just clean, inspect and refit and use the service kits?
I'm really tempted to do this myself as it's not rocket science but needs to be right.
Regards,
Kev.


The venturis in the DCOE 40 31's are held in by an internal spring clip, there is no external screw to lock them in place as there is on some other Webers. You can just pull them out from the front of the carb. They come out in two sections.

The jets don't wear unless they have been abused during previous cleaning attempts, so provided they are clean and undamaged they should be Ok.

cheers
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PostPost by: KevJ+2 » Sun Sep 28, 2014 9:23 am

Thanks Rohan, I have a workshop manual for the webers but nothing on the spring clips. If there seems to be no movement on the spindles, is it best to leave them be, lubricate the bearings, or change them anyway for new sealed ones? Can you think of anything else to change whilst things are stripped, other than using a service kit?
Regards,
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PostPost by: AHM » Sun Sep 28, 2014 9:40 am

Changing the bearings is making a rod for your own back!
Lubricate them and make sure that the new leather seals prevent vacuum leaks.

Many say that the choke (enrichment device) has little or no effect. Make sure that the cross drillings are clear and you will find it has a huge effect! lotus-carbs-f40/weber-cross-drilling-size-t30358.html
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