Not sure what you mean,,,during start,air from whatever source you are using(APU,ground cart) is directed directly to the starter motor(some small turbine kind of motor) via the start valve.
If you can imagine the air has to get from the source (APU,Ground Cart, Cross bleed) to the engine. I think the JT8 has the bleed valve down stream from the start valve duct junction. So for the air to get to the start valve it has to pass through the bleed valve first. I think. This was why it was important to check the start valve had closed otherwise the engine, when on speed, could continue to drive it's own starter moter even if the bleed valve was closed.
As I say, I'm relying on memory here as I don't have the schematics handy.
