http://www.heckflosse.nl/wheel4.htm
Look at figure 28.
You preheat at position B-you feel spring pressure(I used to do it for half a minute)...then pull the knob a little harder (to position C)while stepping on the gas pedal..and "wrrrroam"-it starts and you just get your hand off the knob-the spring will bring it back to "driving position"(D). You may also need to use the primer pump,to saturate the fuel filter housing and injection pump...air in the fuel system may also hinder starting and cause rough idling...Also check glow plugs.Good luck!