I believe its a 1978, but for sure its a SRX 440 L/C. I went through the carbs many of times, rebuilt the fuel pumps and check the vent in the tank. It seems to have plenty of gas going to the carbs. But when its warm up it will barely move itself. it probably doens't help that the clutch has a stall around 5-6000 rpm. It did run super fast for awhile but this started happing. I work on it last winter and still havent resolved the problem. When i first got the sled it didnt have a CDI or stator plate or the wiring. I got that all resolved. Could the issue be in the timing? When i start it, it takes a few minutes to warm up but its running a low idle. Once its warmed up you can hit the throttle and the idle will stay around 2500 rpms. I really like riding this sled since its pretty fast and i dont have much money in it (under $400). Its not in bad shape i gave it a new paint job a couple of years ago. If somenone has some heplful tips i would be happy.

when it warms up Eh!
I would do a compression check on her to see how those piston's are holding up.
You also mentioned clutch....Maybe it's just a busted spring in there could be that simple.