Maintenance & Technical > KX500 Original

Bike tries to grenade itself.

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booneylander:
OK so here's the problem. I took my bike out for the first big ride the other day, and as I was slowing down at one point it just started to rev the piss out of itself with the clutch pulled in. Not knowing what was going on, I hit the kill switch and nothing happenned, it just kept revving the piss out of itself. I ended up coming to a stop and then with the rear brake on I fed the clutch out in 1st gear and managed to stall the engine (without much effort). Put the kill switch back to "run" and it started up again and everything was fine.

During my whole ride it would, every now and then, seemingly quite randomly but perhaps more while decelerating, all of a sudden surge forward and want to rev itself silly again. As soon as it would I'd just lock up the rear wheel and stall the engine and then it would start itself again once I let off the brake(while rolling) and everything was fine for a while.

Doesn't seem like it has much power to rev itself, like it doesn't feel like it's staying WFO, just enough to surge ahead, feels like maybe it's staying 10-20% open or so with the throttle.

I'm thinking it's just a matter of cleaning the carb out in case the throttle is staying stuck open or something BUT, the thing that's really worrying me is that when it starts to rev itself, I can't kill it with the kill switch, which is really weird because the kill switch works perfect all other times. It's almost as if the engine is dieseling.

Anywhoo my first step will be to take the carb apart and clean it all out and check the jetting, lube the throttle cable etc.,  but I wanted to throw this problem out there in case anyone has any other ideas/theories about what the problem might be, and if there's anything in particular I need to check while the bike is apart.

It's an air-cooled '83 motor in case that makes any difference.

FactoryPhil:
Sounds like you have an air leak. Most common place is at the left crank seal or base gasket. I would find the problem before you ride it anymore.

BDI:
That sounds typical of what a bike does when It Is running out of gas It could be an air leak but given Its intermitent nature it could be a sticking float or something pluging the main jet or something else along that line. I would definately say It Is leaning out for some reason You will have to trouble shoot the bike to figure out why

Johnniespeed:
  That happened to me too, except it was on wet leaves, the bike spun around and ran over me. I still have the rear tire tracks on my pants. I thought I broke a rib that time.
   When that happened to me, it was just after a series of bumps. The throttle  did not stick, but the engine "ran away " Also the kill switch does not stop the engine. What I believe happened, is that the float or needle valve stuck shut, the engine leaned out and revved high.
  The bike has never, ever done that again. I have closely inspected the needle and seat for debris, but none was found.
   A KX500 at wide open throttle when you dont want it, is quite a surprize.     John

don46:
Had an 87 that did that, turned out the slide was worn, and when in the right spot it would stick, cleand the carb and installed a new slide, life was good again. I think the 83 used a Mikuni like the 87.

Once your bike gets above a certain RPM the kill switch will not shut it down, pretty much true with any two stroke that uses a ground to kill.

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