Lotus Elan

fuel dribble into airbox

PostPost by: Roy Gillett » Tue Apr 21, 2009 7:52 am

I have a small dribble of fuel from the cylinder no. 3 bellmouth interface with the airbox backplate into the bottom of the airbox. It occurs only when the engine is running (or has just run). My question is where is it coming from? I have renewed the gasket between the front of the carb and the back of the backplate, which seems to have stemmed it but I can't see where it might be coming from and why. Any Ideas?

Roy
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PostPost by: cabc26b » Tue Apr 21, 2009 1:29 pm

Not quite sure what a amount a small dribble is , but when I last had fuel leaking back in to airbox and or out of the carb mouth it was float and or needle valve related.

George
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PostPost by: rgh0 » Thu Apr 23, 2009 11:05 am

The leak is caused by fuel leaking though the gap between the carb body and the secondary venturi insert. The 40DCOE has a spring that holds the insert in place firmly up against the carb body where it matches the main jet passage that supplies fuel to the secondary venturi but this spring looses tension over time and a leak results around the outside of the venturi insert as you observe when the einge is running on the main jet.

Even with a good spring you can experience a leak so making up a small gasket to seal the inserts at the carb mouth is sometimes needed.

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PostPost by: Roy Gillett » Sat Apr 25, 2009 7:53 am

Thanks Rohan,

I should have made it clear that I have Dellortos on my car. I know they are very similar to Webers, does the same apply? I have replaced the gasket between the airbox backplate and the carb. Will that do the job you describe? Finally I have a pair of old Webers (not really serviceable) Can I canibalise them for a spring to locate the venturi (if that is the way Dellortos are built)?

Many thanks.

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PostPost by: alan71 » Sat Apr 25, 2009 9:01 am

On the Dellortos it's held in place with a screw and lock nut.

Alan
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PostPost by: rgh0 » Sat Apr 25, 2009 9:33 am

Hi Roy

The Dellortos usually dont leak and the screw lock used in them seals better than the Weber spring . Check that the locking screw is tight as it clamps the secondary venturi into place and normally ensures it does not leak by pushing the seondary venturi againt the carb body where the fuel passage is located.

The gasket between the carb and airbox does not seal the end of the carb between the body and the secondary venturi. If you have a leak you need to try to seal the venturi with a sealant or gasket.

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PostPost by: Roy Gillett » Tue Apr 28, 2009 8:21 am

Thanks everyone,

It never ceases to impress me how much knowledge there is around in this forum and how generous people are with sharing it. I have checked over the nut securing the venturis on all the chokes of my Dellortos and though none appeared loose, backing them off and retightening seems to have stopped the dribble. AND I understand a bit more about the way Dellortos are put together.

Thanks again

Roy
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PostPost by: elansprint71 » Wed Jun 20, 2012 10:57 am

I have the same problem with a dribble from one Dellorto choke only- cyl #2. I nipped up the aux venturi screw and lock nut (it seemed tight already) and I also checked the float level; it was drooping to 25mm, which seems correct but was closing the valve at about 20mm, rather the 15-17mm (depending on which guru you read). I set it, as best I can , because this is a fiddle, to about 16mm.

Could the float level have anything at all to do with this leak, seeing as the other choke does not seem to have the leak? I can't run the engine until I've got a cam-cover gasket from CN later today.

If not- any other suggestions?
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