Read my spark plug (video)

poorman9

poorman9

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This spark plug has maybe 200 miles of riding on it. It's from the left cylinder which has started missing pretty bad lately. If I put my hand behind that exhaust I can feel it firing maybe 2/3 of the time. The plug looks kind of oily, but it isn't. That black stuff is really hard, I can't even scrape it off with my fingernail. So it's not an oil deposit, or if it is, for some reason it's crusted on there.

To really see what's going on here, click through this link, load the video in 720 or 1080 (by clicking the gear icon at the bottom) That'll give you enough detail to really see the issue.




Any ideas?


Thanks!
 
Oh, I thought oil fouling would be more... Oily.

So next question, oil in my fireing chamber would cause misfiring? I'm assuming yes. Common culpurates? Don't say valve seals. Been there lapped that.
 
Really bad oil fouling is, oily. Slight oil fouling burns and leaves a hard/shiny surface. This black scale builds on the plug's ceramic insulator, giving the spark a grounding path. You could abrasive blast the plug, or replace it, and it'll probably run fine for awhile. Could go to a hotter plug to burn-off this buildup. Ultimate fix is top-end overhaul. However, some engines brought back to life after years of sitting sometimes reseal, and the fine/light oil fouling can go away.
 
Yeah I overhauled the top end two summers ago. Honed the cylinders, new rings, new seals, new gaskets, new valves and springs. Pretty much the works. Any reason not to run hotter plugs?
 
Super-hot summertime, lean fuel mix, long periods of hi-speed driving, bad ignition timing, hi compression ratios, and oil mixing with fuel, can all lead to preignition with overly hot plugs. You just want a plug heat range that'll keep the plug clean, so edge into it one increment at a time.

This is just a band-aid fix. Could keep you going for awhile. If it gets better, great, then dial-down to cooler plug. If it gets worse, it'll be easier to find at teardown.
 
Well I tightened them down a bit, I don't think they were really loose. Also cleaned my carbs and adjusted my cam chain tension.

It doesn't seem to be missing as much, getting 150psi on both cyl. But I can put my hand behind the exahsut and feel the other side is pumping a lot harder than this one (with the black plug).

Any reason to check valve lash? Also I'm not getting any smoke at all. Shouldn't that tell me that it isn't an oil leak?
 

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