Lotus Elan

40DCOE carburettors

PostPost by: ken douch » Mon Jun 20, 2005 5:27 pm

What are the features of a -18 unit and where else is it used? Do modern fuels affect the rubber and gaskets on older carburettors? Do owners find the recommended jets optimum? Using a pair of 45DCOE9 assemblies with 34mm chokes with a 1600cc L1cam, improved top end power at the expense of tractability.I have reverted to 40 bodies with 33mm chokes which makes the car more pleasant to drive on the road.
I would like to hear of other owners experience.
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PostPost by: type26owner » Tue Jun 21, 2005 1:55 am

Welcome Ken,
I might be able help a little. I'll answer the questions in the same order you asked them.

Don't know exactly but my 26 had the -18s as stock.

Nope no problems, in fact you can slightly modify the new style rubber cover gasket and use it on the older carbies to stop the weeping from the paper gaskets.

The stock mainstack jets (115main & 200air) with 30mm chokes and F11 emulsion tubes are problematic and run like crud. I recommend 100 main and 120 air correctors. The 120 size air corrector has about 1/3 the area that the 200 one does. This adds enough air to get adequate two-phase flow but does not wipe out the vacuum signal from the auxiliary venturi at the same time.

Do you have problems? If so describe them and I'll point you in the right direction so you'll know how to fix them quickly.

I've posted tons of info here on this forum but the search capability is next to none so it's pretty much useless now.
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PostPost by: rgh0 » Tue Jun 21, 2005 11:33 am


You can get good road usability up to 36mm chokes at least in 45DCOE's but it requires good tuning to get the off idle transition to the main jets working properly. L1 cams are not great for road use with a big hole in the torque curve around 3000 rpm so carb and ignition timing setup is even more critical.

The listed Weber setups used by Lotus over the years for 30mm, 32mm and 33mm chokes are all problematic to some degree and need tuning to get to work properly with modern fuels. They probably also really needed it when Lotus first came up with the settings. Of the standard setups I find the 33mm one used in sprints works the best in a standard road engine with the matching sprint cams for Australian fuels.

Keith has done lots of setup work for his current Californian fuels. Not sure how well the specific seting would translate to other locations. However his tuning techniques can be used to establish the best setup for any location and fuel witout spending lots of money on dyno time.

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