I have an 03' 400ex with a curtis sparks exhaust, 11:1 compression piston, k&n intake, 152 and 42 jets, and a shindengen cdi box.

I have been reading that its the cdi box that causes the weak spark and the hard start. Its about an inch or so shorter than the stock one. I put it on a friends bike and he had trouble starting his.

If this is the problem what cdi should I buy?

 

I've never heard any real compelling reason to not just run the stock cdi box. From what I gather the only upside is that you get a higher rev limit on a bike that stops making peak power well before the stock limit anyway.

 

sorry its not the stock cdi. its about an inch shorter and if its hooked up to my truck battery it starts no questions asked. it has a little higher rev limit on it and its supposedly off of some honda dirtbike. I'm not sure if it changes the ignition timing or anything and there are no numbers on it.

 

maybe a valve clearance check should be done.

 

I only have about 6 hours on it since the last valve clearance check