I was going to do a flight this morning with my instructor (instrument lesson) and I did the run-up (It was 34F (~1C) outside, but the airplane was in a 50F hanger all night) and the drop was about 300 on the Right and a more typical 140-ish on the Left. Normally it's about the same 140-ish drop on both sides.

It was also running rough on the Right and I noticed the EGT's for #1 and #2 were much colder (Maybe 250F to 300F) than #3 and #4 (maybe a red herring).

All other engine parameters were normal (oil temp was about 130F to 135F). The engine/airplane has about 80 total hours on it and I did an oil change 2 weeks ago (oil analysis was fine).

Hmm.... It's been running fine up until now (it's been at least 20 degrees warmer until now). Maybe some plugs are fouled? Extra cold air revealed the issue? I'll pull the plugs this weekend and see what's what.

It was beautiful this morning at 6B6... Too bad we didn't fly.

Screengrab from a Rotax-Owner.com video on installing plugs. Not much thermal paste should be applied.