[[KSP 1.8.1-1.11.X] Interstellar Technologies]

I've tried to make a craft using the coaxial SSTO engine, but for some reason I can't control the throttle when I'm using it. even though the craft has enough power and liquid hydrogen, because I can't change the throttle the engine never works?

[[1.11.x - 1.12.3] Galaxies Unbound: A Stellar Odyssey™ [1.3.1]&[1.4.3] [27June 2023]]

Are there any good tutorials on how to get to another star?