Bike tries to grenade itself.

[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.

[gowen]

When the bike is running super lean, it will rev itself to death and have no power, unlike WFO (which has full power). I agree with a serious air leak, do not ride until fixed or you your '83 will have serious damage.

[BDI]

 If you turn your gas off and let the bike run out of gas It will do the same thing and the kill switch will not stop It because the air fuel ratio Is lean and running on detinanatio like a deisel It needs no spark thats why the kill swith Is useless. The best way to stop It Is to hold both brakes firmly and let the clutch out

[Hillclimb#42]

 Sounds like you also may have damage to the cylinder. Cheaper to look. When they lean out like that, they are getting way hot and the cylinder is hot enough to keep it running. I agree that the slide is sticking or cable is pinched. Throttle should be "snappy". Pull it back and it should snap closed. Dirt in the throttle tube, or anything can cause it to hang. I also agree that air leaks and running out of gas causes the crazy runnin you describe. Usually though, when you are running out of gas, you run out. It usally dies with some pep, or pukes. The most important thing is get it fixed. Nobody needs to be on a K5 with a sticky slide, or any other possibilty. Nothing good can happen riding that bike. Good luck! Post your findings. My bet is the slide. Maybe someone should start a poll.

[BDI]

 Take your bike turn off the gas sit ther and let the bike idle tell It runs out of gas If your jetting is right as the float bowl emties the bike will rev to the moon and you cant do any thing about It with the kill switch. go try It if your bike does not rev up as it runs out of fuel your bike Is to fat This is a old tunig trick to find out how close your jetting Is on the pilot.your bike will do the same thing if the floats are sticking shut. as the float bowl emties out the engine will rev up I like to put the bike against a wall with the bike in gear so when the engine starts to rev I can kill the engine by letting out the clutch. This Is a trick rick peterson tought me. rick own's rpm he makes the Ice cube cylinder for the thumpers. I would star by cleaning the carb If your throttle Is sticking that will be obviuse. To look for vacume leaks use starting fluid with engine running spray starting fluid aroud the carb and intake if you have any vacume leaks the engines idle will change noticably when you spray starting fluid on it. vacume leaks usally do not come and go, sticking floats do. clean the carb and chech your throttle cable for bussted strandes up close to the throttle housing.

[booneylander]

Wow sooo much info in just one day, thanks a bunch guys for all the opinions/options.

I think my first step will be to take the carb apart and see if there's anything obvious. If I still have the same problem, the next step will be to find air leaks.

I had a look and the rubber boot between the carb and the reed is pretty badly cracked so I'm thinking that might be a source of air leaking, so I'll see if there's anything I can do to seal it up temporarily and find out if that's the problem.

[BigGreenMachine]

The boot is an easy fix. Go to the hardware store and buy some rubber tool handle dip and coat the outside of the boot with it. Seals it up great.

[fluffy]

hey i tried that shut off the gas test but my 500 just stopped. what next?

[booneylander]

Well I took the carb out and removed the boot and reed as well. The boot is cracked on the outside but the cracks don't go through so I can't imagine that would be the source of any air leaks.

Disassembling the carb is next on the list.

Just out of curiosity, what do you guys think of my plug?

[billygoat500]

that bike is definatly leaning out intermittently,check the fuel system,clean the carb. Get this fixed now!!! I have a friend that was tuning up a CAN-AM for his nephew.
He took the bike for a spin after working in it, and the idle air screw came out. he said it made more rpm's than a F1 car. he tried to use kill switch but it wouldn't shut off. (bits of carbon in chamber glowing red!!) he eventually shifted into higher gear and dumped the clutch. bike would not stall and swung around. His foot got caught in the rear sprocket and removed his leg below the knee. He said they found parts of his leg 100 feet away. Got air lifted to hospital. He now is the proud owner of a prosthetic leg wich belive it or not has a "FOX" shock absorber in it!! The moral os this story is fix that now!!!! Oh yeah is the idle screw loose???

[booneylander]

So, what's a good carb to put on this bike 

I started taking apart the carb and noticed that the slide is badly worn on the exterior of the thin skirt, on the side opposite the idle screw.

My local Kawi dealer "can't" (or doesn't feel like it's worth his time to investigate), get me a new slide, OR a new needle, or a new float, no carb rebuild kits available... his words "The bike's what? 25 years old? All the parts are sold and they aren't making any more, so I can't get you any of that stuff".

I'm not one to argue with people that stand behind counters all day, so I had a look at Ronayers and Bikebandit, and it looks like I can get what I need from there. Only problem being I'm in Canada and cross border shipping sucks, and is a hassle and all that junk.

So I got to looking on eBay and I can buy a brand new carb for anywhere between 150-300$, so I figured why not just go that route?

Anyone have any insight as to what would be THE carb to have for my older, air cooled machine?