Lotus Elan

carburation

PostPost by: worzel » Wed Jul 12, 2006 8:34 am

Morning all!

Not an elan problem but I've not had any response from the Excel owner forum so apologies.

I've run a non se excel as an everyday car since 2000 without real problems but have never been able to work out the following-

The car always runs faultlessly- idles pefectly "flat" (if that's the correct expression), never fouls plugs, no flat spots etc but why do the idle screws on the forwardmost carb require a lot more turns outwards than the other?

I first thought that maybe the previous owner had opened up the air bleed screws by too much and that to compensate for the increased airflow the mixture strength had to be increased (if this is how they work that is) but starting from scratch and closing them all down then rebalancing the airflows disproved this.

All jets are correct, as are chokes, float heights, no air leaks, compressions equal, valve clearances to half thou from maker spec- in short I've checked all of the obvious. My elan uses similar dellortos and these I bought new about 8 years ago. The idle screws on these are all approx the same turns out.

Any ideas ?

In anticipation- thanks for the input.

John
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PostPost by: rgh0 » Wed Jul 12, 2006 10:08 am

John
I dont see the same problem on the Delortos on my Esprit or Plus 2. A few extra things I would check you have not mentioned.


Checked the actual throttle plate position The relationship of the throttle plate to the idle fuel entry can affect how open the screw needs to be to get the same flow. However if you have substabtially different throttle plate postions at idle you would need very different bypass settings to get acceptable idle flow balance so I suspect this is not your problem.

You also need to check idle air flow balance to confirm that each throat is actually drawing identical air flow. If air flows are equal then fuel flow through the idle screw should also be identical and if everything else is the same you should have the same number of turns open approximately.

The next thing to check is whether the size of the holes in the carb that the idle screw seats in are the same and the idle screws are identical and not worn in the tapered area. If the holes are smaller in one carb then more turns open required to get the same fuel flow. If the tapered area of the idle screw is worn on a couple this could affect it. Damage to the tapers and holes normally occur if they are inadvertently overtightened down fully closed.


An interesting academic exercise but provided the car runs right it does not really matter why

Rohan
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