Rough running at 2500 RPM

After 200 hrs did the spark plugs get changed and was the 100 hrs service done?

I have done a 100 hr service twice and both times changed the plugs, the last 100 hr was 25 hours ago.

Double checked the fit of the spark plug connectors on the sp and the electrical connection to their cable yet?

merry x-mas

I have cut back the plug wires 1/4" same issue. Swapped the module input plugs, the RPM drop moved to the other switch. I put the input plugs back and swithced the outputs and the RPM drop moved to the other switch. This eliminates the modules and everything before them and narrows it to down to 2 specific coils. 

Hello Walt,

now i got a brand new 912 UL with nearly the same problems, esp. a little roughness < 4600 rpm and a roughness at idle. At the RunUp at 4000 rpm there is a drop at one ignigion circuit of  approx. 50 rpm and at the other there is a drop of 150 up to 200 rpm. After a wide range of problem findings i find out that the cause was the new rotax spark plugs. For the first start with the new Rotax spark plugs this give roughness but the drop at the RunUp at 4000 is equal at 50 rpm but after a 1h flight the drop is like described before. I got a new set of the new Rotax spark plugs but the result was exactly the same. Now i am in discussion with Rotax about this. The old spark plugs from NGK are working well but i must use the new one because it is a brand new engine.

Please check which spark plugs do you use and give response.

With best regards.