Lotus Elan

plug fouling and smoke

PostPost by: tdafforn » Wed Jun 29, 2005 9:14 pm

Dear All,
Got in the car this morning and found that it was running on three cylinders, drove the 3 miles to work hoping that it was just an ignition fault due to dampness (we've been having lots of thunder storms!). Unfortunately it didn't clear. Got home and pulled the ignition leads in turn and identified the duff cylinder. Switched leads no change. Then notices that if I pulled the lead off the plug a little until I could hear it "click" the car ran on four cylinders. Pulled the plug, it was wet and quite sooted up. I replaced the plug and we're back on four. went for a drive and had a load of black smoke which eventually cleared. I now think the reason the plugs fouled was me running the car on the choke for too long during warm up while checking the colling system after a core plug replacement.
The questions are:
1) why did pulling the lead partially off revive the cylinder
2) why did I get loads of black smoke out the back?

Cheers for any help
Tim
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PostPost by: hatman » Wed Jun 29, 2005 10:10 pm

Pulling the lead off the plug, creating a small gap for the elctrickery to jump, actually boosts the spark at the plug electrodes - why, I do not know (but undoubtedly someone on here will). A number of years ago I bought a gizmo that boosted the plug spark by introducing a gap (inside a transparent tube) that you adjusted for optimum performance by screwing the thing in or out. Can't say I had much success with it, from memory, but there you go.

As far as the black smoke is concerned, it seems more than likely that while you were running it on three cylinders a build up of oily cack accumulated in the duff one and this, of course, would be incinerated as soon as the new candle started doing its stuff. Does that help?
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PostPost by: types26/36 » Wed Jun 29, 2005 10:28 pm

I agree with hatman, by making the spark jump a gap the (cant think of a better word) but intensity of the spark is increased, by the sound of it your car needs a "good blast" to blow the cobwebs out. I would think your plugs are choking up and are not self cleaning which comes with not reaching a high enough temp....use of choke......short trips.......idleing along in the traffic etc.
May be a hotter??? spark plug would help, as for the smoke thats just a build up of oil/carbon because the type of driving you are doing and should clear with a bit of sprited motoring.
Brian
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PostPost by: 1964 S1 » Thu Jun 30, 2005 12:07 am

I never use the choke, with Webers or Strombergs. I feather the throttle a bit to keep 'em running during the first minute or two of driving if I come to a red light, but fortunately the first one of those is far from my house. I recommend using the choke only for an occasional cold morning start up (ie; if necessary) to avoid fouling the plugs. My two have their own starting "personalities" but generally I crank 'em over a few times to prime the system, stop, then crank while pumping the gas a bit, and more if needed, then,,, that sound we all love to hear...
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PostPost by: berni29 » Thu Jun 30, 2005 3:16 am

In 8 years of driving my plus 2, including right through winters (the car lived outside in the UK) I never used the choke once. I used to prime with a couple of strokes on the accelerator and wait a sec before churning. I did have an oversized battery though. I was looking through a mag the other day and saw a standard size battery with twice the cranking power. It uses some sort of spiral inside and was bright orange. No acid to leak either from what I remember. Expensive though. I will get one wen the car is back on the road.

All the best

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PostPost by: tdafforn » Fri Jul 01, 2005 7:34 pm

Thanks guys,
gave the car a blast today and all was OK...
My starting routine has changed since I rebuilt the carbs. Used to start after a few pumps of the accelerator. Now seems to need the choke, possibly as a result of running a little leaner..
Cheers
Tim
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PostPost by: type26owner » Fri Jul 01, 2005 10:44 pm

Tim,
The cold start choke works fine if you just tune it. The stock jet is okay only if you live above the arctic circle (way too fat). If you've got it retuned correctly it should fast idle at about 2000 rpms after about 15 seconds. This unit compensates for the lack of enough latent heat from a dead cold induction system. It's a real pleasure to have it working correctly, none of the throttle blipping is necessary. I posted this info awhile ago in this forum but finding it now is almost impossible. I'll pull the top off a carbie and pull a jet out if you wish to rejet yours. Let me know.
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PostPost by: tdafforn » Mon Jul 04, 2005 11:47 am

Hi,
these are Dellortos, do you have the jetting for them?
Would be great to have...
At the moment it actually works pretty well for starting. Turn the engine over twice to prime. Pull the choke out about 1cm and she starts on the button, no need to pump. Then put the choke in and within a block the engine has settled.
On another note, when I was investigating the plug fouling I notice that on 2 occasions a "massive" spark jumped from the engine to the brake servo on the exhaust side inner wing. Jumped all of 15 cm. Is this just the result of it not firing on the fouled plug?
Cheers
Tim
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PostPost by: type26owner » Mon Jul 04, 2005 1:44 pm

Nope, you've got me there. Likely they would be the similiar though since they both use the same Weber jetting. Can tell you how to find the right jetting the trick way though. Rather than buy every available size and then swap and suck. I used fine sized pieces of wire to partially block off the passages to downsize for testing purposes. Only had to buy one set of jets to correct the problem that way.

You HAVE to fully open the cold start units to operate it correctly on the Weber. Not doing so defeats the specialized atomizing capability of that emulsion tube unit. Suspect the Dello probably copied that too. That's why I said it will fast idle at 2000 in a few seconds if all is well. If you pull it full on and it sputters and dies that's a clue!

That plug is not just fouled. It's internal resistor has opened up to infinite resistance most likely. The spark will seek out the path of least resistance to earth itself. Have you checked your earthing strap from the engine to the chassis lately? To be safe and reduce the ground loop effect I have an earthing strap across both sides of the engine bridging the compliant mounts. Also to reduce the bad electro-chemistry effects the radiator should also be earthed. Sparks should not be jumping from the engine to earth ever.
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