912ULS soot on plugs. 100LL or carbs too rich?

[Targhee]

Hi, I recently just bought my first light sport with a 912ULS. Just had the plugs changed out as part of the 25hr inspection and all 8 were completely covered with black soot. The A&P said this was a sign of the carbs running too rich, but the plane manufacturer says it's because it was running the first 25 hours with 100LL (I just switched over to MOGAS 93 E0) and that as long as the engine is running smoothly, I should just keep going and check the plugs again at the next maintenance interval. They can't both be right. Any advice? Thanks!

 

[Dana]

 

[TFF]

 

[delta]

 

[Swampyankee]

 

[Targhee]

 

[Dana]

 

[Rockiedog2]

 

[Swampyankee]