If everything is working properly, it should turn your motor over. Just a couple of things to check. First, are your compression releases working? To check, while the motor is cool....feel the compression releases in the very center top of the rocker box when you press the start button. You should feel them click down to release compression and make turning the engine easier. Next, do not use the enrichner and do not give it gas while trying to start. The enrichner will foul your plugs and giving it gas will increase compression making it harder to turn over. Just give a couple turns of the throttle before pressing the start button but none while actually trying to start it. When you say, "catch the engine" do you mean spin the motor? Do you sometimes press the start and just hear a spinning noise but the motor doesn't turn? That's another issue all together.