Something you might want to check is the TPS (Throttle Position Sensor). I still have my RX-1 but don't ride it as much as the other sleds I have but was getting it ready for the riding season. Last year, I cleaned and sync'd carbs like I always do but noticed when I took it for a spin, it sputtered out the hole and did not run as strong as years past. This year, I did the same but this time, after doing some research on this site, I decided to check my throttle position sensor to ensure it was not only working but was also set correct. I know in the past guys have played with this sensor adjusting the voltage (ie rotating the sensor) at idle (closed) throttle position makes the ignition timing begin its advance run earlier. All I wanted to do was ensure it was set to stock, stock TPS settings range from .710 to .775, and mine was way off that. Once I got it back to the stock position, the sled runs and idles great like it always had; although I did re-sync the carbs after the TPS adjustment. Not sure if this could be your problem but wanted to mention it.
To adjust the TPS, you loosen the 2 phillips head screws securing the TPS to the left side of the 1st carburetor on the carb rack as your sitting on the sled. With the plug still connected, slip one lead of the voltmeter into the black wire and the other lead of the voltmeter into the yellow wire. With the ignition key on and the kill switch not depressed and the engine not running and the throttle closed, see what the voltmeter says. Using the voltmeter, I also rotated the TPS forward and back to check the voltage increased and decreased as I rotated to ensure there were no bad spots (ie bad throttle position sensor).
