KX500 Wont Start!!!!

[cass]

hi guy`s can you give any ideas why my kx 500 90 wont start?  just ran- in ! out last week coughed then died, changed plug fired once then nothing. ive reset floats, checked all wiring with ohm meter within tolerences , mag & stator ok !if you put fuel down the cylinder she still wont start! pull the plug out and its still sparking ! tons off compresion full engine rebuild . surely it sould cough or fart or something? ive never had this problem with a 2 stroke in my 25 year playing with them! not check reeds yet but should still fire with a shot of petrol down the head? fresh fuel in it as well ! woodriff key is perfect and timming bang on! engine has had every seal  & bearing done as well !

[martinfan30]

Something has to be off. You only need compression, fuel and fire to light up.

How good is the spark? Fat and blue? Stator may be failing.

[tharden]

I would say your timming is off.  Maybe your flywheel had rotated on the crank some how?  If you have the three needs for a engine to run then one of the variables are off.

[Friar-Tuck]

 Have you checked to make sure the flywheel key hasn't sheared?
   EDIT!
Sorry, I see you checked the key on the flywheel...

Will she run if you pull/push start?

 
  There is another post here a fellow had the same set-up whith his 450, after tons of money replacing parts it ended up his flywheel/mag was bad.
  I'll look for the thread...  See below
Tuck\o/

[kwakman]

sometimes they pop and bang out the zorst like there gonna go when woodruff key has sheared. check here first, then timing, then fuel and filter.have you just oiled filter? sometimes if not left to dry sufficiently they dont allow air flow, hence not running.........

[Friar-Tuck]

   
Read through this thread please,  Sounds like alot of similar circumstances.
http://www.kxriders.com/forums/index.php/topic,2854.0.html
 
 Tuck\o/

[KXcam22]

Cass,
 It sounds like the flywheel.  Did you remove the flywheel to verfy the key is intact?  Let us know. There are also instances where a plug will foul enough so it won't fire under load (in the cyl) but will when removed. Cam.

[cass]

cam22,   key is perfect ! brand new plug as well ! do you think it could be cdi ? how can i test it ? what ratings should it be kicking out?

[KX500freak]

Cass,
 It sounds like the flywheel.  Did you remove the flywheel to verfy the key is intact?  Let us know. There are also instances where a plug will foul enough so it won't fire under load (in the cyl) but will when removed. Cam.

yeah had something similar today,my moped wouldn,t start good for ages..
now it was dark and i was running again 
looked down ,saw the spark escape trough a gap in the plugcap
maybe check it like that too??

[92kx5]

definitely check the CDI.

[Johnniespeed]

If you have a friend with a quad, try to pull start it. I submerged a cr250 completely under water. Took about fifty feet of pull starting to get it to fire up.( yes I dried out the air box first.)
 The fuel is known good?
  The spark is known good?
    The compression is known good?
I am sure you are getting tired of the same old questions from everyone, but good compression at the right time, good spark at the right time and the right amount of fuel in the combustion chamber at the right time. IT SHOULD RUN.
 John

[cbxracer30]

My 5 has a 44tron and sometimes the floats stick and floods the cylinder. When this happens it won't start and I have to turn off the fuel, remove the spark plug, put the bike in gear and either just push it around or pull it a bit behind quad -in gear- then put the plug back in and it fires right up. then turn the gas back on.

[KXcam22]

cass,
  Is your plug wet or dry after you try to start it multiple times? It is possible that it is the CDI. Sometimes they fail weird before they die outright.  I once had one go (non KX) under your circumstances - after a rebuild.  As I was breaking it in on a slow trail ride the bike began seizing repeatedly.  It took about 7 or 8 seizures before I got back to the truck then it wouldn't start, which I attributed to the multiple seizures.  In my shop I found no spark then tested the cdi which proved to be bad.  Last thing I suspected - I was expecting an air leak.

If you are putting gas down the plug hole and it still doens't fire then there is either, no spark, no compression, or spark at wrong time.  Those are the only 3 possibilities. Sounds like you have ruled out the first two so is has to be the third, "spark at wrong time".  That can only be sheared flywheel key, damaged impulse pickup, or bad CDI.  You have ruled out one of these so it could be, "damaged impulse pickup" or "bad CDI".  An ohm meter should verify the pickup (you might have already done this) - you can have heat issues with pickup failures but that is not the case here.  Sounds like "bad CD" is the winner.

Heres some suggestions:

1. CDIs arn't cheap. It would be nice to borrow a cdi and try it -but hard to find.
2. Try kicking it over with a timing light on the flywheel to see if it fires at the mark.

Hope this helps. Cam.

[Hillclimb#42]

 I would still want to check reeds. It seems like it would do something with fuel poured right in there, but might have to be right mixture to kick. Also, another way over obvious suggestion/question, did you swap plug out? Could have been a bad plug that you recently put in. Try not to eliminate things completely, because you already checked. Also, check jets in carb for debris, petcock for flow, 

[kxpegger]

Check the kill switch.

A buddy of mine replaced many parts including the CDI module just to find out that his kill switch was bad. His was an intermittent problem. Once the bike died the vibration would stop and the bike would usually start again. Sometimes he could ride for hours before the kill switch would act up.

The symptoms you describe don't really point to the kill switch but it may be worth a try and a cheap fix.