What causes cdi box to fail? the big red ran fine,but when trying to resart it the next day it will not fire. Also how do I know if it is truely the cdi box?

Can be any thing -- next time happens need to figure out if problem is spark or fuel --- possibles that don't throw code fuel pump. Fuel filter air filter. Egr valve crankshaft positioning sensor Ignition switch Coil Etc these are just some of reasons have scanned for possible pending codes

4_30_2013, Debug of Big Red 250ES Spark issues ...

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www.youtube.com/watch?v=YumZsSlBhhs
Apr 30, 2013 - Uploaded by Harvey Spooner
4_30_2013, Debug, of, Honda Big Red, 250ES, Spark issues,. Trying to figure out why this, Honda ATC, has ...

Do you have a teather switch ? I would suggest start by checking the resistance of the on off switch . Then procede to the cdi relay. If you do not know how to test such items let me know and I will break it down step by step.

Rarely will both coils fail. Try disconnecting blk wire with yellow stripe from cdi. Check fire again, if fire is good you !likely have a bad ign switch. If there is still no fire, you will need to test trigger, stater. Also remember the can position senor. Test denser to specs. If cambsenser can't tell cdi where number 1 piston is, there will be no fire. Let me know how it works out for you.

It is a toss up. You can check the pulse generator with an Ohm meter. A nice dealer can give you the specification. You can test a CDI box with an Ohm meter , it can test good , and still be bad. The only good way to test a CDI is part swapping with another working bike. Most dealers will not let you return an electrical part and there is a restocking fee.

3 thing cdi / magneto / coilcheck to see if you have power to the coil and cdi and get back to me

I would bet main fuse or spark box. if one spark box is bad, you lose the tach and a pair of cyls. Switch the boxes. Now do the the other cyls drop out and the tach keeps working? get a couple of spare boxes on ebay for $25-50. Also check main fuse for hairline crack.

could be stator or the coil or cdi box

i can give you a little help, the rectifier is part of the charging system. it converts110volt from your alt. to 12 volts. it sounds like you have covered all the ign. possibiltys look for something simple ,like bad connections broken wires ect.