Lotus Elan

Stromberg running rich

PostPost by: Heuer » Fri Aug 13, 2010 11:22 am

Just had the spark plugs out of my Elan and the front two are text book sandy brown, the rear two are black. Having read the manual I understand there is no fuel mixture adjustment on the ZS carbs so does this mean a rebuild or could it just be the needle in the rear carb needs re-setting? The carbs were re-built in 1995 when the car was restored (by Peter Day) and have only done 5,000 miles since. So is there a quick fix or do I order a full rebuild kit (?30 per carb) or get them professionally re-done by Burlen?

Thanks

David
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PostPost by: 69S4 » Fri Aug 13, 2010 1:27 pm

Is this something that has just changed recently? Usually when the carbs starts to wear out the various seals to admit more air weakening the mixture. If it's running richer (and you haven't touched anything :lol: ) then a few possibilities come to mind immediately. Firstly, have you checked that the choke mechanism is returning to the off position? Check the cable is free and the return spring is working properly.

Next, the extra fuel is coming from the float chamber - either through a problem with the float height or the needle valve. I would have thought though that you'd have noticed something more than just sooty plugs if the prob was in this area - flooding for example.

Thirdly, a problem with the needle. They are adjustable up or down but that's not a tuning aid, it's to allow for eg variation in jet height. If only one carb is playing up it could be a broken needle (not in the bit you see but in the part that's fixed into the air valve. (That was the cause of my running rich problem).
Stuart Holding
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PostPost by: Esprit2 » Fri Aug 13, 2010 7:39 pm

What Stuart said, but I'd put a priority on checking the float heights and weights first.

A float that leaks or absorbs fuel will get heavy and ride lower in the fuel... heavier = richer mixture. Weigh both floats on an accurate gram scale. They should both be the spec weight, and they should be the same weight.

Then set the float height. Again, both should be to spec, and both should be the same. Be accurate.

Regards,
Tim Engel
Last edited by Esprit2 on Sun Aug 15, 2010 4:32 am, edited 1 time in total.
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PostPost by: ivor badger » Sun Aug 15, 2010 12:51 am

Check the rubber diaphram. Take the rubber and centre boss needle holder out and hold it up to the light. Gently stretch the rubber diaphram and see if there are any holes. Don't remove the diaphram from the centre boss as you will never get it back on, that old they grow.
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PostPost by: Heuer » Sun Aug 15, 2010 10:01 am

Many thanks for the input. I will investigate all these options.

David
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E-Type S1 OTS
E-Type S1 FHC
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