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Inspired by the posts on ignition and AFR, I took my plugs out for a look. I have an 83 GSL, stock Nikki, about 100 miles on direct fire upgrade. I warmed it up, parked at idle for 10 sec, turned off the engine. Idle at 800 RPM.
The leading and trailing plugs are different in appearance, which seems reasonable. However on the trailing plug, I'm surprised to see there's some rust around half of the periphery where the electrodes are attached (detail below).
Is that at all normal? Otherwise, do you think the colors are normal?
Rotor 1, Leading is more gray that tan, Trailing plug is mostly beige, but shows rust
Idling won't tell you much with plug chops. That tuning should be done by ear. Set your idle to the speed you want. Then lean out the mix till the engine sounds like it wants to die. Then give it a half a turn back to the rich side and you're done.
Plug chops are best pulled when you are doing a steep grade in 5th gear. Get to the bottom of some hill (a long one is preferred) Put your car in the highest gear possible. Then pull the hill in that gear at the throttle position you want to test. When you approach the top of the hill DON'T IDLE. Shut the engine off and coast in neutral till you stop. Then you pull your hot plugs out. This will let you know generally what AFR you are going through at that particular throttle position. Idling the engine will destroy any info you can gain from a pull like this.
As for the pictured plugs... they look fine. A little lean but not too bad. If you want bump up to the next highest fuel jet size, but you did spend a long time idling before pulling them so I wouldn't make any decisions based on these plugs.
Actually looking at your plugs from idle is a good indication of the cruising AFR. Its not
perfect but consider when cruising your are mostly using the idle circuit for the most part.
The leading looks rich to me or too much oil. Are you premixing by any chance? The trailing
looks a little leaner. What you want is a nice light tan color fairly uniform on the plug
electrodes and the center ceramics.
What Q says is true, you can't just do idle to base your tuning on. You need to do a
procedure like he described for the various RPMs or conditions you want to check.
Not premixing. But I don't get on the highway as much as I'd like, mostly just local short trips, enough to warm it up, go in a shop, drive another 5 minutes back home.
I love the suggestions, so practical. Honestly don't know what I would do to tune anything other than the idle air fuel screw. Gotta go read all of Jeff20B's threads and get more educated! Is it all drilling/filling air bleeds and and different jets? That stuff is way beyond my skills.
This chestnut says there are no screws to mess with for anything above 2K rpm.
when looking at plug color, you want to look at the porcelain, and the one you can see yours is a nice brown color.
if it came out brown after a highway cruise, i'd say you might go a tad leaner. if it came out brown after some WOT action, i'd say you were just about right.
just due to the way that the rotary has the spark plugs almost in the exhaust, the plugs do not color like a piston engine. basically you want to tune it to run the best, and then plug color should just confirm you're not too lean or too rich.
for example. we tuned Fungus Mungus's car on the street, and since we ran out of time, and it was on the street, we left it rich up top. we took it to the track and it ran ok, but i really wanted to go leaner. after the first session, we pulled plugs and they were ok, but dark, so if i had remembered my jets i would have gone leaner.
if i had pulled plugs and they were white, that would have been a clue to look for fuel delivery problems, or go richer.
example 2, my car is rich too, wideband says 11:1 at WOT, but i pull plugs and they look great, so i'm considering the engine happy, and leaving it alone.
10-25-16, 02:29 PM
