Lotus Elan

Dirty Plugs And A Miss-fire

PostPost by: Hamish Coutts » Tue Jul 20, 2004 12:39 pm

Hi guys,

Got an Elan +2 S130. I'm having trouble with sooty and sometimes oily plugs.

Set up is Lumenition (original), sports coil (doubtful of vintage but it has a white top), new NGK plugs and Delorto carbs (I am told that these were overhauled 3 years ago). Fuel is supplied by a Facet red top pump via a filter king regulator.
All plugs seem to be equally sooty. Engine sometimes runs on 3 cylinders when cold and missfires a lot at anything over 5k revs.
New o-rings, thackray washers (set at 40 thou gap) and nylocs have been fitted recently though the trouble was there before that.

Any ideas?

Regards,

Hamish. <_<
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PostPost by: types26/36 » Tue Jul 20, 2004 1:22 pm

Carbs flooding? (needle/seats leaking) fuel pressure to high? float level incorrect?
floats punctured?............incorrect jets? idle jets to big? mixture not set correctly?
I've read reports Dellorto's are prone to flooding when standing overnight, some have resorted to fitting electro shut off fuel valves.
rgds Brian.
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PostPost by: types26/36 » Tue Jul 20, 2004 1:25 pm

Oh! lets not forget air filter blocked.
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PostPost by: worzel » Tue Jul 20, 2004 6:37 pm

Try the dizzy- is it advancing?

I've always found Dellortos seem to start on three cylinders when cold (or it certainly sounds like it) then they pick up. When cold try holding it at 2000 revs for about 20 seconds and see if then idles normally.Unfortunately it's difficult to diagnose at a distance but when it starts to misfire next time pull out the choke- if the problem disappears/reduces you're too weak (could be wrongly jetted- if it gets worse you're running too rich.

I'd try the simple things first- servo pick up leaks, headlight pick up leaks, as others have suggested sticking floats/needle valves, blocked main jets, plug gaps etc are the things to look at.

Good luck

John
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PostPost by: gjz30075 » Tue Jul 20, 2004 10:38 pm

I would try a new set of plug wires. Might be the weak link in your ignition system, if plugs are new and coil and lumination are working. Ignition system should be top working order before going to the fuel system.
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PostPost by: Hamish Coutts » Tue Jul 20, 2004 10:38 pm

Thanks for the replies, really appreciate them.
So far have cleaned the plugs and cooked them with a blow lamp and guess what - fires on all 4 on tick over, sounds very docile actually.
Floats OK and fuel levels seem ok in float chambers. Not sure about fuel pressure as can't check that and also don't know what the pressure should be - any ideas?

Still misses at 5k+ though. Could this be due to the carbs vibrating too much and foaming the fuel in the float chambers? Is 40thou the correct gap for the thackrays? They seem to have enough movement.

Also does anyone think that it's worthwhile replacing the coil/ignition system? If so what coil etc. - or is that just pouring money down the drain? What about a decent set of plug leads as I don't know how old the present set are?



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PostPost by: 1964 S1 » Wed Jul 21, 2004 4:25 am

Are your lights bright at night? I'm running original old generators and notice a definite rich running and high rpm bobbling problem if my batteries get low. Webers or Strombergs. A good battery/charge and highway drive have cured it more than once.
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PostPost by: gjz30075 » Wed Jul 21, 2004 6:21 am

I think the thackerys call for .035 but I'm sure .040 will do the trick, too, as long as the 'O' rings are in good shape. The high rpm miss could be the coil. They're relatively cheap so its worth replacing.

Greg Z.
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PostPost by: types26/36 » Wed Jul 21, 2004 6:41 am

Could be wrong here but as far as I remember fuel pressure shoul be approx 2.5 to 3.0 psi, you would need a gauge to check.
40thou is fine although I doubt its frothing as I've seen solid mounted carbs running O.K.
Its worth checking the dist cap and leads for resistence particularly if you have suppression caps/leads, you dont really want more then about 10k ohms but you need a meter to check this.
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PostPost by: Hamish Coutts » Wed Jul 21, 2004 8:39 pm

Thanks for all your replies - really usefull advice and much appreciated. Hope I can reciprocate.

Best regards,

Hamish.

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PostPost by: SteveMaddison » Fri Jul 23, 2004 11:13 am

Suggest you also check rotor arm and points. Had lots of problems with miss fire and poor running.

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PostPost by: paul_mescall » Fri Jul 23, 2004 1:38 pm

Having had the same problem for many years, after sorting the ignition system and petrol system I still had the problem, my solution has been to run with a 1mm lower float level than book and 1 hotter NGK plugs. I cannot remember the number as it has been so long since I had to change them.
Champion plugs I found failed(carbon short) much more quickly than NGK plugs.
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