I only get a click when I try to start the Razor quad bike

Thoughts -
No/poor connection between power source and motor
Motor failure
Only someone with their hands on the bike can fully diagnose.

http://www.razor.com/wp-content/uploads/2011/11/DirtQuad_Manual_v.3_12-10.pdf

I have exactly the same problem and it started right around the time the "gracious" 90-day warranty period expired.....
The battery lights had been on for days, indicating a full charge, but nothing happens when turning the throttle. Battery housing is very cumbersome to open, but I'll try to disconnect the battery next.

I need help! My son mx650 is charged, but won’t run. Put weight on it won’t move but lift rear tire off ground and runs full throttle

yes!your battery needs replacement.....throttle clicking after a full charge is a sign,...but that's after 2years or more,depending on how it's being used..your motor can go bad before then if you been riding in the rain--wet connectors in or out the motor can not get wet for any reason..a full dirt motor bike can not get full dirty with mud..mud catains water/water and electricity don't mix/////.motor/thottle/moisture.

Sounds line the stater motor gear is stuck on the fly wheel. Have a mechanic check it just to be safe.

ITP tires

The batteries should be 2 x 12v giving an output of 24v anything less than this the Razor Dirt Quad will not run. always make sure you buy genuine Razor replacement batteries.

The Main controllers always seem to be the problem on these quads. If you have a voltmeter you must check the batteries for a complete charge. You should read 24volt or around 24.60 vdc. If you have a full charge usaully 12-16 hrs by the charger supplied with the quad. Than check the output to the motor by disconnecting the motor wire and put your leads in the sockets and verify if you are getting voltage to the motor. Make sure you re-connected the battery before testing the controller output. You should see a varying voltage from 0-24 vdc when the throttle is turned. If you do not see anything at the motor lead and your batteries show charge. the controller is faulty or you have a bad connection. Un-plug and plug and connectors.

Well this post was done a long time ago, seems like you have a bad battery. you should see 24vdc. The batteries are in parallel so it adds up to 24 volts.If one of them is dead it would only show 12vdc.

sounds like the CDI box is shot. This should be located either under the seat or the left rear side of the fuel tank if memory serve me correct.Fairly cheap part 20- 25 bucks.