1985 kx500 popping sound???

[outlaw]

I race cage karts and I have a 1985 kx500. during the last race i broke a ground wire. motor popped a few times when it broke then got back to the pits and fixed the ground wire and went out for the next race and the car would idle fine but once you started to get on the throttle the car would cut out and fall on its face and pop a little. So we loaded up and brought it home. replaced coil and still having problem. took it to a kawasaki mechanic and he tested the coil, and the stator and both were perfect. tried firing it up again and again it would idle but once you give it throttle it would fall on its face and pop really loud then the motor would die. now the motor wont fire at all just pops.......there isnt much fuel in the bowl of the fuel filter so were going to replace the fuel pump and replace the ground wire because it looks a little rough. anyone got any ideas what could be my problem???

[DoldGuy]

Sounds like a sheared flywheel key.
DoldGuy

[outlaw]

When we pulled the flywheel off to take a look at the stator the flywheel key was perfect. no damadge to it at all...

[DoldGuy]

Have you put a timing light on it to see whats happening with the advance?

[Friar-Tuck]

Hey Outlaw,
  (Sorry Gold, I couldn't type this fast enough! checked the woodruff key)
 
I think I would pull the carb and verify the fuel/float level.  While the carb is off pull the reed block and have a look for cracks or chips.

 Make sure the fuel pump wasn't damaged and verify it works, (it is an impulse pump correct?)
 Check the Fuel line and vents are clear.
   If that all checked out, I'd look for good spark, the cap and plug wire look O.K.? 
  Then the kill switch,  and then  check the timing.
Whew!
  Hopefully one of the guys will recognize your symptoms and say "Oh yea that happened to me"
     Hang in there!
 Tuck\o/

 

[kxpegger]

CDI?

[Friar-Tuck]

Dang!
 Got me there Pegger My good man.  That is also a part that has to have some Kawasaki black magic thing to test it...

[outlaw]

Thats what were down to... I got the motor back on the car this morning tonight were going to check all the fuel lines and fuel pump and replace the ground wire because it looks a little rough. if its still not fixed im guess the cdi fried when the ground wire broke... which if thats the case my season might be over unless i can find someone that wants to sell it for cheap or just donate me one...

[The Flyin Hawaiian]

I was out on my 500 this past weekend, I was on a dirt road and I got on the gas in 5th when my bike popped real loud. Kinda like a backfire. I pulled the clutch in and coasted to a stop, it was idling but would rev past idle. I checked the usual stuff and ended up trucking it home. It ended up sucking a reed.

[outlaw]

we checked reeds a few nights ago and they looked perfect. 

[Polar-Bus]

I race cage karts and I have a 1985 kx500. during the last race i broke a ground wire. motor popped a few times when it broke then got back to the pits and fixed the ground wire and went out for the next race and the car would idle fine but once you started to get on the throttle the car would cut out and fall on its face and pop a little. So we loaded up and brought it home. replaced coil and still having problem. took it to a kawasaki mechanic and he tested the coil, and the stator and both were perfect. tried firing it up again and again it would idle but once you give it throttle it would fall on its face and pop really loud then the motor would die. now the motor wont fire at all just pops.......there isnt much fuel in the bowl of the fuel filter so were going to replace the fuel pump and replace the ground wire because it looks a little rough. anyone got any ideas what could be my problem???

I say it a million times check the simple things first ! Poping is primarily "lean" fuel condition. Popin however can also be ignition related, but this is more of a rare occurance. Like Doldguy commented KX500's are know to backfire and shear the FW key.  Generally from my experiences either CDI's work perfect, or they don't work at all.  Same goes with the internal ignitor. external coils go bad, and sometimes can be a PIA, as ocassionally when the coil get hot spark weakens or fails, then when cold the coil fires spark again.

I would first start out with a fresh spark plug, do a compression check, then check for adequate fuel flow. Pull the carb for a complete cleaning.

[kwakman]

polar bus is right about popping often being related to lean running.however, i have had an intermittent cdi fault early on in ownership which had me looking under all the wrong rocks.if you havent had a gasket failure/carb or fuel pipe blockage and the rest of the electrics and reeds/cage are good,try finding someone else who runs same motor and 'swap' cdi's.if you do experience flywheel woodruff key issues in future,use valve grinding paste to lap flywheel to crank,making certain to keep paste away from crankseals and clean taper and flywheel of paste properly afterwards.it won't shear again.K.

[outlaw]

So here is the latest news. We have everything back in the car. brand new ground wire. all brand new connections. its getting fuel. no blockages in the fuel lines. carb is perfectly fine. pulled the spark plug out and set it on the head of the motor only to find out we have no spark at all now. soooo my question is would it be the cdi causing the "no spark" situation. As a said earlier i took the motor to a kawasaki mechanic and he used his OHM tester and tested the coil and stator and they both tested good. pretty much the only thing left is the cdi? or am i missing something?

[Friar-Tuck]

  Sounds like your right on.
The system is only those 3 pieces, well and the flywheel .
 There was a guy here a few years ago who had a bad flywheel. They tried everything at the dealership and at home.
    A tech at the shop had a flywheel off another bike and tried it and that was it. but that was one in a jillion...
 
I don't know what early years parts interchangeability is.   The early years have a lighter flywheel and different timing curves.   
  I guess what I'm trying to say is I can't send you my cdi off my 2000 and have it work with your '85.
If you can't come up with an '85 cdi, you may have to get a whole new set-up, to the best of my knowledge.
 Let me see what I can find..
Tuck\o/

Here's one
http://www.kxriders.com/forums/index.php/topic,9470.msg74609.html#msg74609

[Polar-Bus]

So here is the latest news. We have everything back in the car. brand new ground wire. all brand new connections. its getting fuel. no blockages in the fuel lines. carb is perfectly fine. pulled the spark plug out and set it on the head of the motor only to find out we have no spark at all now. soooo my question is would it be the cdi causing the "no spark" situation. As a said earlier i took the motor to a kawasaki mechanic and he used his OHM tester and tested the coil and stator and they both tested good. pretty much the only thing left is the cdi? or am i missing something?

Like Friar commented, to test for a bad CDI you do a process of elimination by testing all the other components via the specified Ohm test. One other simple test try unplugging your kill switch. KX CDI's kill spark via a "ground out" system.