Lotus Elan

Plugs after a run

PostPost by: richardcox_lotus » Fri Aug 23, 2013 3:01 pm

Thought I'd post this. Went for a run this a.m. In hot conditions, so engine temp was warm all the time really (90+). Traffic jam nonsense occasionally but a bit of motorway running as well. Total mileage about 40 miles with stop midway.

Car runs ok - is nippy & doesn't fluff too much at lights,etc. on webers & occasional pop on overrun.

Is the consensus that I'm running too lean or that they look Ok ? I don't want to richen the mixture when the car generally runs Ok.

image.jpg and
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PostPost by: Pistacchio sprint 72 » Fri Aug 23, 2013 4:17 pm

the two first ones from top of the pic are light chocolate brown and ok according to me.

However the 3rd one and fourth one at the bottom are clearly lighter. The 3rd one especially, nearly white.

So i may allow myself to think the two plugs of the bottom are fed with a leaner mixture from that carb than the other ones from the other carb.

Either it is a carb set up to do or you may have an air intake between the rear of the carb and the intake manifold.

For example a cracked o ring...


But wait to read the others diagnostic...
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PostPost by: richardcox_lotus » Fri Aug 23, 2013 6:35 pm

Forgot to add - top to bottom is cylinders 4,3,2,1. These are NGK 6's which have served me well in the past.
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PostPost by: StressCraxx » Fri Aug 23, 2013 6:39 pm

Richard,

I agree. Third one from the bottom is lean, 4th just a bit lean. It may be something as simple as idle mixture screw adjustment, but check for vac leaks too.

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PostPost by: AHM » Fri Aug 23, 2013 7:54 pm

So here is a different perspective...

It is a photo so different focus and light conditions for each plug. Also the bottom two are at a different angle.

I'm looking at the body, ceramic, centre electrode and outer electrode for each. ie no3 ceramic is white but body and both electrodes are dark so 3 looks like 2 to me.

From too to bottom
4. A little dark
3. About right
2 About right
1 A bit light

They seem quite good to me if 4 has the oil breather and 1 the vacuum take-off.

Edit. Having thought some more - Webers are fixed once you begin to open the throttle, so go for a good blast and check them, then go shopping and check them.
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PostPost by: richardcox_lotus » Fri Aug 23, 2013 8:45 pm

Ooh I didn't think of any effect of the vacuum takeoff at that end of the intake manifold.

And I do have the inlet breather by #4 - which is probably the reason it's dark.

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R
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PostPost by: rgh0 » Sat Aug 24, 2013 12:21 pm

They all look OK to me and within the good range. Most Elan's looks much richer

Why are you running "R" plugs - they cost more than standard NGK BP6ES and don't make any difference for a road car or for that matter a track car either as far as I can tell.

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PostPost by: richardcox_lotus » Sat Aug 24, 2013 1:13 pm

Hi Rohan - I got the R plugs a few years ago when I was first looking for some NGK6s. I don't recall them being more expensive at the time but I've no real thoughts about whether they are better or not. My understanding is that the R stands for "resistance" - ie they don't upset the neighbours TV as much.

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PostPost by: Pistacchio sprint 72 » Sat Aug 24, 2013 1:29 pm

It will not interfere to electronic devices in the car like autoradio...
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PostPost by: billwill » Sat Aug 24, 2013 3:53 pm

richardcox_lotus wrote:Ooh I didn't think of any effect of the vacuum takeoff at that end of the intake manifold.

And I do have the inlet breather by #4 - which is probably the reason it's dark.

Regards
R


I would only expect that to have an effect if you have a brake servo. If the vacuum is used only for headlight lifting the engine would soon suck up all the practical air from the cross-member and the mix would stabilise until each time the headlights were raised, providing a bit more air in the pods to suck out.

On the other hand a brake servo will 'use up' some of the vacuum every time it is used, letting air back into the big chamber of the servo which in turn will dilute your fuel mix on Cyl 1.
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PostPost by: Pistacchio sprint 72 » Sat Aug 24, 2013 6:01 pm

Unless there is a leak...
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PostPost by: richardcox_lotus » Sat Aug 24, 2013 7:08 pm

Yes Bill there is a Servo.

And currently it doesn't leak.

Although tomorrow's another day !!

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PostPost by: Pistacchio sprint 72 » Sat Aug 24, 2013 8:48 pm

When i meant leak for the servo, i did not meant fluid leak but for example a crack in the rubber vacum hose, this would lead to suck extra air and make the mixture leaner
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