Lotus Elan

Leaking Stromberg choke

PostPost by: Harvey » Tue Nov 02, 2010 11:58 pm

Gas gathers and slowly drips off the fast idle cam on the front Stromberg of my 1971 +2S. I have noticed this after the engine is turned off and the car sits overnight. I have not checked it while the engine is running and I suspect it does not do so then.

I have disassembled the choke and replaced the two gaskets holding the spacer block and the choke to the carb body but it still leaks. I have also corrected the float heighth to ensure that gas level is not so high that it might spillover into the choke. But the choke still leaks.

I suspect the spacer between the choke disc and the carb body may have something to do with the leak because I cannot find a picture of this 1/2" thick piece of metal in either the +2 workshop manual or in the Haynes Stromberg book. The spacer has a brass pipe at the top which connects via plastic tubing to a brass pipe on the rear carb. This was fitted to the car when I bought it from the PO 12 years ago. Is this a breather of some sort? I have spoken to two knowledgeable Lotus people about this spacer and tubing and neither one could explain what function it serves. If the forum members cannot help me my plan is to remove the spacer and seal off the rear carb brass pipe and the hole in the front carb that lines up with the spacer tube.
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PostPost by: billwill » Wed Nov 03, 2010 2:35 am

Sounds like a home made balance tube. (supply a photo?)


Discussion on this forum has indicated that a balance tube is essential for strombergs lotus twin cam.
Bill Williams

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PostPost by: Harvey » Wed Nov 03, 2010 4:22 am

Bill,

Thanks for your reply. I will post a picture of the spacer and plastic coupling between the carbs tomorrow. You should know, however, that the U.S. emissions equipment has been removed from the car and a Euro high crossover pipe manifold had been fitted to the car by PO.
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PostPost by: 69S4 » Wed Nov 03, 2010 7:42 am

Hi Harvey

Your description of the spacers and connecting tubes does sound odd. Unless the US versions have extra bits I'm not aware of (quite possible!) the whole assembly shouldn't be there. The choke system is very simple being just a small casting covering a metal disc with a number of different size holes that rotates to allow fuel through the holes. A spring holds the disc against the carb body and an external spring on the spindle returns it to the off position. Stick a cable on and that's it. No spacers or connection between the two carbs other than the cable.

There is a small hole (1/2mm?) in the casting and over a period of time I've noticed a very small amount of staining from fuel weepage but I've never seen liquid fuel there. Post a picture if you can.
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PostPost by: oldelanman » Wed Nov 03, 2010 7:50 am

Harvey wrote:Bill,

Thanks for your reply. I will post a picture of the spacer and plastic coupling between the carbs tomorrow. You should know, however, that the U.S. emissions equipment has been removed from the car and a Euro high crossover pipe manifold had been fitted to the car by PO.


Hi Harvey,
From the diagram in the workshop manual it looks like the rear carb did not have a choke in the federal emissions set-up. Did the PO fit one when converting to the european spec ? If not maybe what you have is an attempt to make the front choke serve both carbs.

Regards,
Roger
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PostPost by: Harvey » Thu Nov 04, 2010 12:37 am

I am attaching a picture of the spacer and plastic tubing between the carbs. You guys are right, only the front carb has a choke.
Attachments
lotus choke 003.jpg and
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PostPost by: oldelanman » Thu Nov 04, 2010 5:05 pm

Hi Harvey,
You could try sending your pic to Burlen or Gower and Lee and see if they recognize that set up - maybe from an installation on another car of the period - but it does not look like original Elan to me. The body of your front carb also looks different from mine, the casting is not the same on the choke side above the fuel inlet connection. I was under the impression that emission and standard carbs had the same basic body but with additional external controls on the emission version - they certainly look identical in the workshop manual - but I could well be wrong on that. Your brass tube connection to the rear carb looks to be where the idle trim screw would normally be - do you have a trim screw on the front carb ?

If it were my car I would be inclined to remove the spacer and pipe and plug the holes. You would also need to shorten or re-drill and tap the throttle lever so that the fast idle adjusting screw lines up with the cam on the choke lever again once the spacer is removed. Incidentally, does your throttle lever look as though it's been extended ? That would be an indication that the installation was "home made" and not original but if it looks unmodified then maybe it was part of an original installation - albeit possibly on another car.

You could also fit a choke to the rear carb while you are at it to complete the "europeanisation" but maybe you don't need a choke at all in your part of the world ?

Regards,
Attachments
Carburettor choke assemby 003.jpg and
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PostPost by: Harvey » Thu Nov 04, 2010 8:01 pm

Roger,

I have no idle trim screw on either carb. You are right about the "spacer" being a fitting to allow the front carb choke to serve both carbs. When the choke is rotated and the starter activated petrol flows from the fitting tube through the plastic line to the rear carb tube. I'm embarrassed to say I have owned the car for 12 years and didn't realize this. When the choke is rotated, gas leaks from the underside of the choke body where the body joins the fitting even though I just fit a new gasket at that joint. It looks like I will have to find some sealant to smear on the gasket that is impervious to petrol.

Although the climate in the Sierra foothills of Northern California is mostly mild, winter temps can drop below 0 centigrade so I'd like to keep my choke.

Thank you for your help. I think my answer is as near as my sealant store.

Harvey
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