check the secondary...If it wont back shift, your starting out in high gear...you need that secondary to close to give you power when theres a load.
Take it off, and take it apart. If the spring tabe don't line up, thats your problem. Also check the buttons and make sure there are no deep grooves in the helix.
For reinstallation, Put the helix on the spring (Notice what holes it's in before you take it apart) Turn the movable sheath 1/3 turn counter clockwise and push the helix down, and put the snap ring on. Get a buddy to help! Once you get it together, twist the sheaths and see if theres pressure. If there is, you did it!
If nothings wrong with the secondary, i's check the primary....Post the the engine size and model and I'll tell you whats suppose to be in it for weights and spring.