I have a 2003 450s Foreman. It will crank and run about 5 minutes the 1st time you crank it for the day. Then it will dye and not star back. It will fire once then it quits firing all together. If you let it sit for a while it will fire again but will not fire enough to crank. It must be electrical but where do i start. Has anyone had this problem or know wahts wrong. I would appreciate all the help i can get. I hate to start buying parts i dont need if i dont have to.    

It sounds like you may have an intermittent electrical problem.  Possibly a loose connection somewhere, or a loose ground wire, or a chafed wire rubbing against bare metal causing a short circuit.  When you say it "quits firing altogether", are you using a spark tester to verify that electricity is getting to the spark plug consistently as you crank the engine?

What about the rest of the ATV? 

Carburetor not gummed up?

Air filter clean?

Spark plug in good condition and electrodes not all worn down?

If it's a fuel problem, you could wait until it dies and won't start, then loosen the intake boot and spray a little starter fluid down the into boot towards the carb.  Then reattach the boot and crank the engine.  If the engine starts and runs for a couple of seconds, then you know you have a fuel delivery problem.  Do this at your own risk, though.  Don't spray a ton of it- just spray for about a second or two.

Do you have a service manual?  The best investment you can make is to get a genuine Honda service manual ($50-something dollars?).  They usually have a troubleshooting section inside.  Otherwise you're going to probe around aimlessly and maybe you'll get lucky and find the problem.  But otherwise you might waste a bunch of time, and spend money on parts that won't fix the problem.  Good luck.  Verify every single thing is working before saying "oh, no, it couldn't be that." 

Yes I have taken the carb. off and cleaned it extremly well,new air-filter and spark plug. I also have been using a spark plug fire tester. the  first time u crank it will run ten minutes or so like a brand new one. Then it dies let it sit a few min and it will fire 1 single time then no more. Just wonder if it is the CDI box or the magneto getting hot causing it .Still just lost as an easter egg . Might check on the manual.Thanks for the help anyother advice would be helpful and appreciated.  Danny

It sounds like what you are experiencing could be a cracked circuit board inside the CDI unit or other electronic box or a cracked solder joint.  Sometimes on cars, what happens is the circuit board inside the ECU will develop a crack, due to vibration or heat, causing an open circuit.  When things are cold, the solder joint remains in contact and things work okay.  But as the circuit board heats up, the joint expands and separates, thus causing an open circuit.  What you could try doing is finding the CDI box or other electronic control unit and lightly tap repeatedly on the box with the handle of a screwdriver as the quad is warming up.  If it acts up when you tap on the CDI box, then you're probably vibrating that cracked joint enough to get it to cause an open circuit and make the engine die.

Intermittent problems are the hardest to track down.  But it sounds like you have a clue if it does it every time after about 10 minutes.  That tells you it's probably heat-related, as the engine warms up.

Still could be a loose ground wire.  Check everything.

Could be the kill switch intermittently shorting out, causing no spark at the spark plug?

I would most definitely spend the money on a factory service manual.  Otherwise you're going to be probing around, checking this and that, not really knowing what you're looking for and getting frustrated.  But if you have a manual, it'll have a wiring diagram and you can systematically eliminate certain parts of the wiring harness.  Be prepared to buy a multimeter and know how to measure volts and resistance so you can test the wiring.

Now would also be a good time to buy a tube of dielectric grease and take apart all your connections and lube them with the grease to keep them from corroding, if they haven't already done so.

I'd also buy a can of compressed air that is used for blowing the dust off of electronics.  It comes out very cold.  So when the quad acts up and the engine dies, try spraying the CDI box or other electronic box with the cold spray and cooling it down.  Then see if it starts back up.  If it does, then you've found your problem, because the cold spray made the cracked joint contract enough to have continuity again.  Unfortunately you can't open the box and re-solder the joint or repair the crack- you have to buy a whole new unit.