Especially for engine problems with a powder special you would probably be better off posting in the ZR forum since the powder special is just a long track ZR. Anyway, there is TPS (throttle position sensor), and TSS (Throttle safety switch). The TPS is the sensor on the throttle body that the computer uses to determine how much fuel to give the engine. The TSS is just a safety switch to prevent a runaway sled if the throttle gets stuck.
To test the TSS, unplug the 3 pin connector up by the handlebars that goes to the kill button. It is on a wire by itself. You will know you have the right one because you will be able to start the sled with the kill button pushed down. You will have to shut off with the key. Ride it and see if the bog is still there. If it is it wasn't because of the TSS. If the bog goes away, see this thread.
For the TPS, see the thread below.