I bought a 400ex a few months ago and haven't taken it out yet!! When I bought it it had a slight tap and was told the valves needed to be adjusted. That was done and the problem still existed. I sent the motor back and they replaced the tensioner and cam. I brought the motor back and put the bike back together and it wont start. It sounds like it wants to but just wont turn over. I even tried pulling it. What do you think is it an electrical problem or something else with the motor? It's not the timing because I checked it myself as well as others....

 

Dont know if it is the problem, but I would check the spark plug first.

 

make sure your gas is on, you have a fresh plug, the key is in it and on and the on/off switch is on and your battery is fully charges. it should fire up. If not start checking your ignition and wiring, as you might have pulled a wire loose..

 

The motor needs three things to start. Spark( at the correct time), compression, and gas.
Pull the spark plug, hook it back up to the wire, hold it against the motor, and spin it over..to check for spark.
Got spark?

 

check teh plug then look to see if your electrical system is grounded just happened to me wouldn't start..turns out it wasn't grounded plus then my plug was fouled from trying to get it to start

 

What about air? better check that airfilter.

 

i had the same tap in the top end and it eventually blew up, i bent all 4 valves boke the tenisioner chain and cam gear and when i got it back it still made the noise, i think its piston slap. right now im having a new piston put in and when i took the stock one out it looked like an egg, when its back together if it stops taping ill let you know