Ignition advance and detonation - would you worry about these plugs?

[John Gervais]

I recently installed a new Distributor Doctor rebuilt/recurved dizzy, and in an effort to get the ignition timed properly, I probably check my plugs more often than I should.  These plugs have probably close to 200km (125 miles) on them.

If you look closely, and I use an 8x magnifying loupe when I examine sparkplugs, I can see a few small aluminium balls on the center electrode (detonation???), and although there is a small area where the fuel film extends completely to the electrode tip, the lopsided 'clean' area is rather prominent.  I've read that a clean-burned ring at the center electrode tip normally indicates too much distributor advance.

The lopsided clean area / fuel film blush is most pronounced on cylinders 2 and 3.

I can't hear any 'pinking' and there isn't any run-on when I turn it off. 

I realize that the air/fuel mixture is a bit on the rich side - yesterday I installed a monometallic jet carrier in the HIF, so fine tuning the mixture is next ...

So, what do you guys  think?

[John Gervais]

Trying to add a picture...  can't.

[94touring]

Should be able to.  Even if they're too big should resize.  Is it giving you an error?

[John Gervais]

Yep - I've tried reducing the size to no avail.

"An Error Has Occurred!

Your attachment couldn't be saved. This might happen because it took too long to upload or the file is bigger than the server will allow.

Please consult your server administrator for more information."

[94touring]

Hmm.  Email me the pics and let me look and give it a try.  Maybe the server is acting up at the moment.  94touring@gmail.com

edit:  I'm having the same issue.  Probably the server being buggy and will clear up shortly.   I'll keep trying and see what can be done. 

[John Gervais]

E-mail sent -

[94touring]

As suspected it fixed itself during the night.

[MiniDave]

They look pretty normal to me......

[94touring]

Oh and they look fine to me too, if anything a hair lean.  You could pull them occasionally to see if they start to erode, but if the car is timed and not pinging you're probably good to go. 

[John Gervais]

I don't think it's too lean, might be from the camera flash - here's a picture from a little bit further away.


I'm using an Innovate LM1 wideband AFR gauge (similar to the AEM) which reads (though it fluctuates wildly, I don't know how I could get it to read more steady) between 12.6 - 13.4AFR at idle and around 13.4 AFR at part throttle cruise.

Maybe the HIF piston 'vibrates'?  If so, how would I make it more stable, or maybe this is 'normal' for this type of gauge?


Hmmm.  I still can't post a picture...  Not from my 'C' drive nor my 'F' drive...

[94touring]

I just tried and it's throwing a different error than last night.  Something going on with the host server.  Not sure why it's been so buggy last two days but should clear up.  Try again in a bit and I'll keep trying too.

[John Gervais]

Super - I've E-mailed a few images which perhaps better highlight my areas of concern.  If I'm successful in posting them, great - if you're successful, great - either way, feedback from the members will be possible, valued and respected.

[94touring]

Still not working. I may have to make some calls. I'll be in the air till later tonight.

[94touring]

here ya go

[John Gervais]

Beautiful job, Dan!

I was afraid I'd have to try to post the pics and crash the website.

So, what do y'all think of the spark plugs? 

The 'distance' picture shows that the insulator is clean pretty much down to the base, and it's got a pretty darkish 'soot', so I don't think it's running too lean, but maybe has a tad too much advance? 

It's those aluminium specs that I'm worried about.  Should I be?

[MiniDave]

Why do you think they're aluminum bits?

[John Gervais]

I believe they're aluminum, as they're shiny and metallic.  I tried to scrape one off and it was bonded to the electrode rather firmly, not like the 'normal' ash crust that forms.

Edit:  Here's the advance curve from the Distributor Doctor - I don't have a scanner, so I plotted it in Excel (Woohoo!  The attachment worked!).  It looks small and unspectacular, but the camshaft is the 997 Cooper camshaft and the cylinder head is a stage 3 Calver ST (C-AHT88):

The second image is of the distributor gubbins - what I'm still struggling to understand.  It's got a 14° cam/stop and the chart says that it provides 10 degrees total mechanical advance.  So, if I set it dynamically with my timing light at 12° BTDC at 1000 rpm (measured at the crank), I should get 32° at max crankshaft rpm (say 4000 rpm and above).  12 + (10 *2) = 32.  In fact, that's pretty much what I get - but where does that 14° cam/stop come into play?  Why wouldn't it be an 8 or 10°? 

As I understand mechanical advance (by reading on the MSD website, Marcel's pages etc...) total timing is the sum of mechanical (in my case, 14° ) plus initial advance (where I set it at 1000 rpm - in my case 12° BTDC) which should be 36° at max rpm (4000 rpm and above.)  But, that's not happening as far as I can see - I've got it set at about 31° at 4000 (thereabouts - I nearly burned my hand off operating the throttle while peering over the timing light strobing on the crank pulley).

Maybe I need a masterclass or special tutelage.

[John Gervais]

Here's the original chart:

[John Gervais]

So....

Any thoughts?

[94touring]

I think you're probably fine.  If you set timing at idle, doesn't ping, sputter, run on, and the air/fuel is set with a wide band you're good to go in my book.  You could buy a knock sensor I suppose or tune it on a dyno with all the gear hooked up. 

[John Gervais]

Sounds like I'll just have to take my chances then -

I don't have access to a dyno (can't afford one - a few hundred dollars expense on the other side of the country on an unemployment benefit...).  My ears are pretty useless sometimes - small ear canals sometimes plug up, so I can't really hear squat, especially when driving it.  I hear the carb sucking and the exhaust farting, but not much in between. 

I've got the wideband installed, but haven't had much luck trying to find out 'where' it should be reading - I've got it set up between 12.4 and 13.2 AFR at idle; the Innovate Motorsports MTX-L gauge fluctuates so much that it's really hard to find out what it's measuring.  The funny thing with this is that I put a Colortune that I've had for over 10 years in it and saw that the Colortune 'Bunsen Blue' color, which can be up to interpretation, can give very broad AFR readings on the AFR meter.  Easy to tune very rich and still have the blue color...

At steady part-throttle cruise, the MTX-L is reading AFR around 13.4 (ish), on acceleration it drops to 11.5 (ish) so I imagine this is ok. 

I'm a member of the local club, but the guys don't really do anything for free...  There's very little community spirit in these parts ...

[94touring]

My major tuning has all been done on turbo rotaries.  I have a wide band installed.  I have the same 13.5 at idle (obviously fluctuates) and stays there at cruise in vacuum.  Ideally you'd shoot for stoich which is 14.5.  I just recently bought the equipment to change my maps as I have some stupid rich areas as well as a lean spot very low in vacuum.  In boost I'd like to go from 12.5 at 1psi down to 11.5.1 at 15psi.  I would think in an na car you'd probably want 14.5 low rpms and as your rpms increase have it down to 13.1, but as rich as 12.1 if you're running aggressive advance and compression.  Of course with a carb it's hard to map it that precisely, and that's where needles probably come into play. 

[John Gervais]

From what you're saying is that I've got it much too rich at idle and could probably take a bit off of the needle to give a slightly richer part throttle cruise and top-end.

I've gotten pretty good at measuring needles and taking a tad off here and there, so it looks like I'll be sorting through the tubes of needles and seeing what could take shaving. 

As to the 'shiny balls' on the spark plugs, I retarded the ignition 1 degree at 1000 rpm and I'll see if the balls continue to accumulate.

[94touring]

Where you say  "At steady part-throttle cruise, the MTX-L is reading AFR around 13.4 (ish), on acceleration it drops to 11.5 (ish) so I imagine this is ok"

I'd shoot for 14.5 at part throttle cruise which should pull full throttle to 12.5 which would be ideal.  If you're too lean at part throttle you'll know cause the car will fall flat on its face.  My lean spot in vacuum at 1300-1500 rpms I hit 15.5-16.5 and it about shuts off.  At 8000 rpms and 15psi it hits 10.1 and starts to miss.  It really needs to be leaned out up top bad. 

[94touring]

I'll also say it must be nice to have a wide band on a mini!  I spent hours tuning these dual carbs on the maroon car.  All I can go by is seat of my pants and how the plugs look.