hello i have been trying to troubleshoot my sons quad for some time now and cannot get past this starting issue. The engine will only try to crank w spark plug removed as soon as i re-install plug i only get a quarter turn from starter. i have checked/adjusted the valve clearance to what i believe is correct(.004) many times, but no luck. is there anything else that would cause hard cranking with plug installed? also i have disconnected exhaust temporarily to exclude any blockage.

 

Put jumpers on the battery and see what it does if it cranks then try useing a 7Y battery rather the 4

 

Have you checked at the starter to make sure you are getting a good 12v? also check when trying to start. could be bad connection. Could also have a bad/week starter. have you pulled the starter apart and checked it out? they are easy to work on.

 

i have not pulled the starter, but do get strong/fast spin of starter when spark plug is removed, so i dont believe it is a starter issue. i always have jumper hooked up when working on it because the battery is constantly drained due to not running. it truly seems like the valves are out of adjustment, but they aren't. i am thinking some sort of compression issue? i have removed exhaust and air filter and still no spin until i remove spark plug...

 

Still need to check the starter under load.. Even a failing starter will work when their is no resistance on the motor.

Maby try doing the valves again. watch a few YouTube vids to make sure you did not miss something

http://forums.atvconnection.com/chin...mm-piston.html