What do these spark plugs tell you?

[variant]

Greetings,

Anyone keen on 'reading' these plugs? The picture sets below show what the same plugs looked like after running the first 500 miles & 6000 miles in a rebuilt type 3 motor burning unleaded fuel. (The file comments are self explanatory.)

[Marc]

The area of interest is actually further down inside, at the base of the insulator, when you're trying to judge whether the mixture is right. Modern gasoline contains some compounds that can complicate "reading" a plug, too, but I don't see anything you need to be concerned about. It was still burning a little oil at 500mi (the black deposit on the shell) but that's clearing up.
Unless you do a "clean" shutoff (switch off, declutch and coast to a stop when under full-load conditions) a lot of what you're looking at on the plug has more to do with driving into the garage than going down the road so you shouldn't obsess about drawing conclusions unless you see an obvious problem.

Never been a fan of Champions myself, I prefer Bosch or NGK. A healthy D-Jet engine can use a plug one step cooler than a stock carb'ed motor (a Bosch W7AC or NGK B6HS is usually right for an FI Type III)

[variant]

I'm concerned that this engine may be running too lean at high rpm - based on the fact that it has been averaging 9.14 l/100km or 25.73 mpg (US) but on the last long trip it returned 8.1 l/100km or 29.03 mpg (US), cruising at 120-130km/h or 75-80 mph. This is a completely standard motor equipped with Solex 32 PDSIT-2/-3 (version VW-118/1 & 119/1) carbs, mated to a manual transmission. (Sadly we never saw Bosch D-Jetronic FI on a type 3 in SA.) Trying to get the car onto a proper dynamometer & 4 gas analyser so see what the engine really does. I have been advised to go one heat value cooler anyway. As for the Champion plugs - loyalty from flying 2000+ hrs behind them...

[Marc]

Worst thing you can do IMO is switch back & forth between Champions and Bosch/NGK - there's just enough difference in the contours of the threads that it'll wear out the heads - so if you're happy with Champs, don't listen to me.
It certainly doesn't look to me as though you're too lean, there's ample tan coloration near the insulator tip. What I go by though is the color at the base of the insulator following a clean shutoff under hi-speed full-load operation...and as I alluded to above, even that method's not as trustworthy today as it once was due to the games the refiners are playing with the fuel composition.
One thing that's still a BIG red-flag warning, though, is the presence of any tiny purple balls on the insulator or electrodes (use a magnifying glass to look for them). They mean there's preignition/detonation going on (contributing factors are lean mixture, too much spark lead, or too low of octane). If there're no purple balls and no refrigerator-white insulators, you're probably close enough to sleep well at night.
Your carbs are the same ones we got in the US in 1967 only, before D-Jet became standard here. The link below shows their jetting (note that left & right are different).
As far as the plug heatrange selection goes, a stock carb'ed engine usually takes the warmer choice but it depends upon the type of driving you do - if 75+ MPH is normal for you, I second the suggestion to go a step cooler...what are you running now? Champion L86C would be the "warmer" option, and L82C the "cooler".

http://oacdp.org/wog69/049.png

[variant]

Thanks for that link - very intersting site. According to that list i have the correct jets in both carbs. I'll look out for the purple balls you mentioned. (Good enough reason to get a proper maglamp - eyesight not as sharp as it once was... )

[hugging corners]

NGK B6HS

isnt that a plug for points only-there is also a same plug with resistor br6hs were 2 stroke bike guys use these
when runing cdi coil instead of points.
would a resistor plug be better for lets say msd type of ignition
i know that those ngk b6hs have a hotter and coller version of the plug also

[Marc]

If you're running stock Bosch ignition leads, there are already 1KΩ resistors in the ends. With a stock ignition system, additional resistance is neither required nor desired.
NGK heat range numbers run counter to Bosch. The higher the number, the hotter the plug in Bosch; for NGK a higher number is a cooler heat range - a B8HS is cooler than a B7HS is cooler than a B6HS, etc.
NGK also makes wide-gap variants, for hi-intensity ignition systems (modern outboard motors, for example)...same plug, other than the electrode not needing to be tweaked so much for ultra-wide gap applications so it stays more parallel and the gap setting remains consistent over a longer time.

"As well as reducing electrical noise for radio, television and mobile telephones etc, many modern ignition systems require resistor plugs to stop electrical noise from interfering with the vehicle’s on-board electronic control units (ECUs). Resistor spark plugs should always be fitted where specified.

NGK automotive resistor spark plugs contain a ceramic monolithic resistor. The resistor filters out excessive electrical noise generated by the ignition system. The most effective place to situate a resistor in the high tension circuit is as close to the spark plug as possible making the spark plug an ideal place to house the resistor.

In nearly all cases – apart from some very old low output ignition systems – resistor spark plugs can be used in place of the non resistor versions with no detrimental effect on engine performance, power output or vehicle emissions.".

[FJCamper]

Hi Variant,

Do you have an oil temp gauge?

If you're running hot, you're too lean.

FJC

[variant]

I use a K-type thermocouple inserted down the oil dipstick tube and MajorTech automotive multimeter with temperature function for periodically checking the oil temp and when setting timing & CO. I find that the oil temp after cruising on the highway varies a lot according to ambient temperature but I seldom see more than about 95 deg C.

IMHO, there are far too many other factors that will result in high oil temperature which makes it an unreliable parameter for confirming AF ratio.

[FJCamper]

Hi Adriaan,

My advice is about quick, human estimation of the situation. You have good instrumentation so you don't have to guess, but this is how we do it in a road race.

Our drivers canot dwell on precise instrumentation. We change carb jets a lot, depending on circumstances. We recently ran Sebring, a 14 hour enduro. We started too lean (Solex 44mm "Kadrons" in a 1303).

We rejetted twice in the first hour, up from 160 to 190 mains, and each rejet lowered our oil temps noticiably. Your 95 C. is good for a street engine. Our lowered temp was down to 115 C.

The point is, with all else being equal, look to air/fuel ratio first.

FJC