I have recently bought a 2003 400 EX with new 11:1 Dome top Pistons, new brain, and new coil and it currently will not start. I was thinking that the problem was due to the timing being incorrect could anyone give me any ideas to why it wont start or how I could get the quad in time. Thanks

 

When you say, new brain, I am guessing a igh rev CDI box? If that is the case, they have an advanced timing curve. I had alot of problems with my White Brothers CDI, so much, that I took it out. Try a stock CDI and a new spark plug.

 

I appreciate the help I am really new to the sport atv scene so idk if that is what i am talking about or not haha is that the box under the rear left fender if so that is what I am talking about

 

I have heard that 400ex's have problems with the timing belt wearing/slacking and the cam can skip teeth, thus retarding your timing.

 

Well ikey this may be true but the quad would run before the piston was changed along with the aftermarket cdi, so I am not sure if this is the problem. Thanks though