I read on here that retarding the timing helps to turn more r's as a cheap mod. It seemed to work for mine. (97 k5) It seemed to be alright on the bottom but stopped pulling once I got past the mid. It is a minor movement, but helped a bunch!!! I would move the timing mark back and see if it helps. What pipe are you running.
By the way I'm running 58 Pilot, 168 Main, 3rd clip position. Of course it is all relative to your elevation, temperature, fuel mixture, humidity, engine mods... everything basically. If you are close to stock then start with stock jetting.
Visually inspect reeds, air cleaner, float adjustment, silencer, carb interior. What have you already tried and then eliminated?