Mixture Analysis - Expert Help Required!

[ianh1968]

Elsewhere on on this forum I made the observation that I find it very
difficult or impossible to read plugs until there is 100miles or so worth
of burn on them.

Further reading told me categorically that I was completely wrong
in this respect. Fortunately, I managed to find some comprehensive
instructions. I got them from the internet, so they'll be gospel, right,
especially if I follow them blindly like the author suggests I do.

I found a straight road, on a hill and drove to it. So far so good, don't
think I'd messed up yet. Changed the plugs. Fired it up and immediately
gunned it up to maximum revs in 3rd gear, which is 97mph on my gearbox...

I cut the engine, as per the instructions and coasted to a stop, managing
in the process to not lock up the steering. I then immediately pulled the
plugs and preserved the evidence. I then drove home again after replacing
the original set of plugs.

I didn't have the stopwatch going, but I reckon that the whole procedure
was over in about 30 seconds, and less than half a mile.

As I said before I am a complete novice at this, but I was quite shocked
at the outcome - I was expecting to see a nice golden-brown/toast/beige
sort of colour on them, you know, like they show in all the manuals etc.

Now I'm no expert on this subject, and don't claim to be, so I need a bit
of assistance here. I am sure that amongst us, someone will be able to
answer my questions.

To my untrained eye, it looks like the plug has ended up with some kind of
shiny metallic covering on it, maybe zinc. I hope that it's not molten alloy
from the top of my pistons! The shiny metal looks like it has got quite hot
at some point during the process, but other than that I am unable to draw
any firm conclusions.

I am providing a photo for reference:

Exhibit-A.jpg

Would the experts here be able to help me with the following questions:
1) The road I found was not quite straight, it had a slight curve in it.
Is this likely to have put a sort of "bend" in my results?
2) Although the strict instructions did not mention this, I used 1st and 2nd
gear before selecting 3rd as I didn't want to burn my clutch out. Is it likely
that my actions will have caused some kind of "rpm-differential bumps" in the
output data?
3) I am aiming for an A/F ratio of between 12.5:1 and 13:1, for maximum power.
Have I achieved this?
4) If not, please tell me which of the 267 SU needles available I should use.
I am using SZ at the moment. Sorry, but I don't know the exact spec of my
engine, but I do have pink furry dice, a 12" steering wheel and a "skull" gear-knob
(Hope this helps)
5) Am I using the correct heat range of plug - These are "Champion".

Any expert advice or guidance in this matter will be greatly appreciated.

Ian

*** EDIT : PLEASE SEE MY POST DATED 18/03/2014 ***

[mk1]

[Frogeye61]

You say that you are looking for 12.5 to 13:1 for best power. I would try to keep it around 13 to 13.5, but either way you would expect quite a bit more black on the plug. It looks way too light and even the outer end of the insulator looks completely white. this says too lean.

What you have done is a one-shot acceleraton mixture test. Not very accurate, but better than nothing. A few more of these will give you a better idea of the burning quality. This is only one field of the needle, maximum acceleration, of which usually most needles are too lean anyway.

A similar test, though over a bit longer time and distance would be the highway test. This should give you the cruising range of the needle, then of course there is the moderate acceleration part and the idle part.

Then you can use a web supplied computer tool like WINSU to investigate the needles available and try to match something up.

Otherwise you could just spend the money and use the facilities of a rolling road dyno. Really it's money well spent.

[Smiffy]

[Spider]

Interesting topic Ianh1968 and I'm glad you've bought it up.

Sorry, this is well beyond me to be able to offer any answers at all, however I am reading on with interest.

I do have one other question, if I may add here;- Why does it hurt when I pee?

Would the expert know if this to do with Mixture or Ignition Timing or could it be both?

[ianh1968]

Would the expert know if this to do with Mixture or Ignition Timing or could it be both?

Spider,

My personal view here is that it could be both. Say, if you've just eaten a whole pack
of "Extra Strong Mints", for example the "Mixture" may be a bit rich and will sting on
the way out.

If the "Timing" is too retarded, ie, you are peeing too late, the pee will have been
in your body longer and will have gained more heat.

Both of these things may be causing the pain.

You could continue to listen to more half-baked ideas that you get from the internet,
or if you are really desperate, go and see a doctor, preferably one with some kind of
diagnostics equipment.

Dr Ian
I am about as qualified as Dr Nick, from "the Simpsons"...

PS: Can we please try to keep to the Original Subject?

[minimans]

Nobody can tell you if it's right or wrong from one run!! do yourself a favor get booked onto a dyno and set the thing up properly. Its really money well spent no guessing involved no trying to divine the difference between golden brown and a light tan colour! Save some money and check and adjust all the basics first timing, tappets etc. no big oil leaks! operators hate having to clear up oil stains.................. You should get a three run base line and go from there.

[Spider]

Thanks ianh1968, I do value your views and certainly will take that on board, however, I would still like to hear from the expert.

[Frogeye61]

Actually I really hate crossing forums, but I thought this deserves it.
http://www.minifinity.com/forum/viewtop ... d42c7562ac
This is a link to a thread documenting locations of rolling road dynos in various parts of GB. I'm sure you will find one close by.

[1071 S]

Plug chops are an ancient and honourable way of setting mixtures. However....

Unfortunately they changed the rules when lead was demonised. We don't have lead anymore - you may, but the amount will be much reduced....and so will the colour changes you are looking for.

The good news is that suitable air/fuel meters are now available ..and affordable.

Cheers, Ian

[ianh1968]

Thank you for all your replies.

My post was NOT intended to be serious:

"Sorry, but I don't know the exact spec of my engine, but I do
have pink furry dice, a 12" steering wheel and a "skull" gear-knob
(Hope this helps)"


The idea was to gain ideas on the relevance of the visual "Plug-chop"
method that has historically been used to "tune" our engines.

I note that there are probably a minimum of two varieties of "Plug-chop":

The first, as described here, is where a brand-new set of plugs is
used, and for only a single and very brief acceleration run.

The second, would be where the plugs have a bit more colour on
them to start off with, and the "Chop" is done after a period of
running at the same load/rpm.

Others?

We don't have lead anymore - you may, but the amount will be much reduced
....and so will the colour changes you are looking for.

This is a very valid point, in fact, the chemical make-up of the fuel as a
whole will be considerably different to what it was years ago. As an
example, years ago, I used to get that black goo on the backs of my
inlet valves, but now this has gone: The detergent, perhaps?

use the facilities of a rolling road dyno. Really it's money well spent.

Nobody can tell you if it's right or wrong from one run!!
do yourself a favor get booked onto a dyno and set the thing up properly.

I completely agree with you both. I did go to one dyno, years ago, where
it was a complete waste of money. The operator had NO NEEDLES and NO
facility for adjusting my advance curve. I did not ask about this before I went...

For a few occasions I used the Aldon Automotive dyno but have now found
a very good facility much closer to where I live.

When selecting your dyno it is important to know exactly what they can
and cannot do with your engine. For example, do they have a good
selection of needles or jets etc? Can they adjust the actual curve inside
the distributor?

I would still like to hear from the expert.

Spider, I hope that you get your "medical" problem sorted...

My final conclusion here is that not even an "expert" will be able to
diagnose an engine and provide accurate advice when there is no
specification available. Even if there is a specification, if this is only
slightly different to a known spec, any advice as regards mixture needles
and/or ignition timing is going to be entirely guesswork.

Thank goodness nobody chose a needle for me...

Ian