What Flying Horse said is good advice. Most new builders will underestimate the amount of pressure needed to disengage the clutch. Push the lever on the engine in as far as you can with your hand and adjust the cable stop so you have no slack in the cable. You'll need an inch or a little more of movement to disengage the clucth. Don't worry, the cable and hand lever can do the job. Just make the cable tight and discard the small spring that came in the kit. Use only the big one because it is a heat shield but the small one is not required and will only increase hand lever force.
Age and Treachery Will Always Triumph
Over Youth and Skill & "Charlie Don't Ride"