I gradually started realizing all was not well, a roughness at the lower RPM's, and hard starting with a reluctant idle. It seems that (at least on the internet) that the instant this issue is mentioned, you hear "you have to sync the carbs, YOU'VE SYNCED THE CARBS HAVEN'T YOU", ( in the past, I have synced my carbs about every 1000 hours, some seem to do it constantly) followed closely by "time to change the plugs" (I change them every 500 hours or so). More obscure possible reasons were a collapsed baffle in the muffler (2200 hour on mine, no way to inspect it inside, that possible reason occupied my thinking for a bit) to having prop blades not all adjusted the same pitch (assuming ground adjustable, mine isn't, so I scratched that off the list), to fooling with the needle for the mid range thingie, changing the main jetting, to rebuilding the gearbox (backlash caused by slop can be a gremlin I heard), to removing/replacing/testing the ignition system. Somewhere in this wealth of information, kind of buried, was "check the idle circuit jets." Long story short, after figuring out where they are (next to the main jet, inside the carb bowl) it was a 5 minute job to get them out, ascertain I could not see light or blow through the tiny hole they have, and then hit them with carb cleaner and some high pressure air with a hose attached to them, removed from the carb of course. After that, I could see light, and blow through them, and a test run up resulted in the long time usual instant start and smooth idle, especially with the 1" cross over tube I now have.
The clogging issue was already resolved, by taking the glass bowl type in line filter off and throwing it in the shop trash can, and replacing with my long time favorite fuel filter, a cheap pleated paper type in a metal canister, by Napa or CarQuest. They have MANY times the square inches of filter media, the other type is more of a screen, in the past, they have been all I used. Upon disassembling the glass filter (it has screw off ends, so you can get at the screen inside, which is retained by a nut on a threaded shaft), it turns out the keeper nut had backed off enough to allow the screen to have about 1/4" gap, allowing unfiltered fuel to reach the carbs, problem solved This backing off of the screen was not evident by looking at it from the outside, it was not evident until I unscrewed both ends. I can see NO reason to use those damn things anyway, like I'd going to look at it (the only supposed reason for their existence is visual inspection, that and they are kinda cool looking and shiny) during pre flight, under the cowl?! The only reason I did, was because they were out of the size of my regular style and I was too impatient to wait, and too lazy to go across town to another parts house.
My entire point of relating this issue (turns out the threaded shaft has holes, obviously meant for a cotter pin, to retain the screen, which went un noticed by me, I never thought I'd need to cotter pin the inside of a filter) is not to bad mouth a type of filter (they do suck though, having a minuscule amount of a crude filter media as compared to the pleated paper types, I have cut into one to compare and it's no contest) but to tell other Rotax fliers: at the first sign of hard starting, rough idling, and general crappiness at below 3 K RPM, before you do ANYTHING else, check the frigging the idle jets. It's quick and easy, just pop the bowls off, easy peasy, KISS!
Pic is of some test flying down the range from my place, having your engine want to die when you throttle back, while landing uphill on skis, and at the same time just getting used to a new vernier throttle installation, makes the work load much higher then normal.
