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@jimvanmorrissey avatar
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Hi all -- just what this forum needs, another "please read my sparkplug" post. Anyway, I've scoured the forum and can't find anybody with these exact same symptoms.

So: this is 600km after a total engine rebuild, with a Malossi 221 running on a SI24 with all the fuel flow issues sorted. Polinibox exhaust. Ignition is at 17.5 BTDC. Squish is a hair over 1mm.

This isn't really a plug chop after WOT, this is after just puttering around town with a few drag races between the lights. I set the jetting up fairly rich for the break-in period -- sure enough, that plug is pretty brown nearly everywhere --and am about to attempt to dial in the jetting properly this weekend.

What's curious is that ash-like white ring around the tip of the electrode. Any idea what that might indicate?
Forum member supplied image with no explanatory text
@socalguy avatar
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bodgemaster
63 GL, 76 Super (x2), 74 Primavera (x2), 79 P200, 06 Fly 150
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UTC quote
The tip of the electrode supposedly gives a rough indication of timing. The conventional wisdom is that a ring >0.5mm means the timing is too advanced, but I don't know how accurate that is or why that would necessarily be so.

External inline image provided by member with no explanatory text
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UTC quote
Thanks SoCalGuy for digging that up. Will first clean this plug up and do some more riding before reading it again, just to make sure this isn't some residue from the first 100km or so when everything was a bit wonky.

Hard to understand how at 17.5 degrees this could be firing too early. Just strobed it. It's a real 17.5 degrees. Are some setups better set as low as say 16 degrees?
@charlieman22 avatar
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Nedminder
62 VBB1T Round Tail W/ leaner sidecar
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UTC quote
Jim - couple suggestions/ my $.02
1. Don't clean the plug. You will be shocked how quickly an already colored plug will alter its colors from your testing.
2. See 1.

Much better in my experience to use a colored plug - and then do your testing with different throttle positions.
If you're not going to actually cut the plug - at least run it (under load - like slightly uphill) at WOT and perhaps half and quarter throttle. Each time - kill the engine and coast.

The darkness of your plug could literally of taken shape just idling at the light for a minute or less - covering up however it looked after you raced it hard.

Colored plug, decent load (hill, 3rd gear, etc) and kill switch with coast down - will give you some good reads.

Oh - and shoot the pics without any flash, using fresh light.
Flash washes out the color significantly.

Good luck!
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bodgemaster
63 GL, 76 Super (x2), 74 Primavera (x2), 79 P200, 06 Fly 150
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UTC quote
In my experience, the burn pattern and color on the top of a freshly cleaned piston after a few miles tells you heaps about timing. Send an endoscope down the spark plug hole and take a gander.
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Thanks folks for the additional advice. @Charlieman, yes, I'm aware that it takes less than a minute of a certain kind of driving for it to leave its imprint on the plug. But would that include that white ring there on the electrode? That's the thing I find so compelling. Never saw that before.

Re looking at the piston head, I don't have an endoscope so Ill just pull the head off and see what's what. I anticipate this'll be a fully black (but dry) head, what with the jetting being intentionally on the rich side. But yeah, I'll give that a clean and see what happens with the next pattern.

And yes, future plug photos will be taken without flash!
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@christopher_55934 avatar
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2007 Stella 225
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UTC quote
SoCalGuy wrote:
The tip of the electrode supposedly gives a rough indication of timing. The conventional wisdom is that a ring >0.5mm means the timing is too advanced, but I don't know how accurate that is or why that would necessarily be so.

External inline image provided by member with no explanatory text
Is the 0.5 mm down the side or the ring on top? I thought it was down the side, by description in picture.
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Not at all, actually -- it's a little cream-coloured doughnut on the top of the electrode.
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