1996 gtx will not rev

[1955rex]

I have a 1996 gtx 800 thats got me beat. I have replaced the mpem modual, rev modual, coils,had carbs rebuilt and still gives me problems, The ski starts fine and will sometime will run fine for awhile then it will slow down to a idle. Giving it gas will not do any good, but keep unpluging the dess key it will finely go past idle and run fine???????