912 excessive RPM drop on lane A

If the temps have dropped about the same time the excessive rpm drops occurred you could try lifting the needles for the main jet to enriched the mixture.

https://www.rotax-owner.com/en/videos-topmenu/elearning-videos/154-needle

At this point I I have suspected carburetors to be my problem from other people‘s posts. I just don’t understand how the carbs could be causing my problem. I ran the engine up to 3500 RPM and I shut off lane B so it would run on a with a 400 mag dropAnd I sprayed starting fluid in each carb so it would Richen  the mixture and it made the engine run worse on both carbs

Did you watch the video on adjusting the needle for excessive rpm drop during during mag check?

https://www.rotax-owner.com/en/videos-topmenu/elearning-videos/154-needle

 I just watch the video. Interesting that it can cause 400 mag drop. The Plane was built in San Diego bought for my guy in Louisiana and then I bought it and brought it back to Reno at 5000 Feet elevation. Oh I put approximately 40 hours on it and it ran fine until now. So if it ran fine before I don’t know why I would need to change the needlesI’m not opposed to trying it it looks simple

If you ran it 40 hours as-is without this issue at your new home station, fiddling with the carb needle jet circlip settings probably won’t solve your problem, but if you decide to have a look at them you’ll need locktite and a heat gun. The video doesn’t mention any of that but the maintenance manual does. Was the SB for replacing the circlips complied with?