Spark plug and oil residue

My IAME 09 was running very good and during my last session, it started to bug down. Low on RPMS (mid 10 to 11) compared to 15k-16k. Went to the pits and started to look for issues, and eventually went to the spark plug. When I pulled the cable, I noticed an oily residue on the top/terminal and a little on the plug cable contact. When I pulled the plug it was very wet.
This was my 4th session of the day with about 12-14 laps on each of the previous ones. I only did about 3-4 laps before it bugged down.
Ideas/comments why this happened?
Thanks for the help.

Clean out all of the oil in the spark plug boot. Install a new plug. If there is oil under the old plug, clean it off, being careful not to push any debris into the cylinder. If the spark plug boot does not fit snuggly around the plug, replace it. Also check for arching from the plug wire to the engine.
This might be a sign of the coil beginning to fail or the oil/fuel is wrong.

Thanks for the tips. Will give them a try.

It concerns me that you found oil on the top/terminal side of the spark plug and inside the spark plug boot/cable contact. There should be no reason for oil to get to those places. The spark side of the plug can foul with fuel/oil which will compound the effect of a wet plug as more and more unburned fuel passes through the combustion chamber. Fuel fouling is usually the result of needle settings on your carb.

At one point, I had an issue with my low side needle backing out of the carb, because the o-ring was worn, not providing enough friction between the needle and the carb. The vibration from the engine allowed the needle to rotate itself loose. This in turn allowed excess fuel into the carb, which caused bogging and fouled the plug. Short term fix is to wrap a rubber band in a figure 8 fashion around the two needles. Long term fix is to replace the o-rings.

Still, getting oil under the spark plug boot is perplexing. Check the plug for cracks in the ceramic insulator. That is the only way I can think of oil getting from inside the engine out the top of the head.

That is a good point on the spark plug. I will check it to see if there is are small cracks on the insulation. I am replacing it, but will check the old one anyway.

If your spark plug isn’t tight enough it’ll leak oil and fuel and compression…

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That is a good point. I will check the tightness when I take it out this week.