Hey all,

New to the forums but glad I have found this. So I've had my GS since September and I have loved every second of it (except November until late March dang snow). But have had it out and running fine for about a month now then I started to loose some power especially in first and 3rd/4th. I also began to hear a high pitched hissing coming from the engine. So I checked the easy things, oil, spark plugs, air filter... all normal and clean and oil had been changed before winter. Then I thought could be dirty carbs so I jumped on here and found a carb cleaning thread and did that, had no issues got it all back together and had the power back, at least in 1st/2nd. I didn't run it any higher than that because the high pitched hissing was back and louder than before. It also will not start without the choke like it had previously (the only time before this that I had to use the choke was twice after the winter while it was still a bit chilly). And it will not idle steady.

Sorry I was kind of all over the place but I hope I can get some insight on this because I'm dying to ride now that it is nice out again.

Thanks in advance! 

have you checked the compression?? sounds like a valve is not seating the whole way.. the hissing, does it sound like its in the intake or exhaust?  I would start there. Lapping the valves is not a bad gig.. I did it. yes it may put your bike down for a week.. Well depending how much you can work on it. There are plenty of youtube vids that will guide you.. let me know if you need more info.

Hissing could be air being sucked in around carb boots or a damaged top diaphragm.  Choke = richer which counteracts air leaks.
You have checked your valve clearances, no?

get a short tube and hold it up to your ear, move the other end all over your bike until you know EXACTLY where the hissing is coming from. (Like a Stethoscope)
I would guess an intake leak.