Hey guys new guy here. Question for someone. I have a 1985 LT50 with a 2002 motor in it. Kill switch and tether work with no problems for a while when my daughter is riding. All of the sudden yesterday the ATV had the chain jump the sprocket (need new set) and idled high as can be. Neither kill switch or tether would kill the engine and to choke it. Got everything back together this morning ran fine while sitting up then all of sudden idle kicked up and the kill switches wouldn't kill it. Don't want a 4 year old on it and it take off on her and she can't kill it. Thanks for the help in advance.

 

For the runaway idle, look at the slide in the carb sticking. It doesn't take much crud or varnish to make it stick.

As for the kill switch not working, I think what's happening is when the RPMs get high enough it's running like a diesel. When an engine gets hot enough, any carbon buildup can start to glow red hot and keep the engine running without spark.

Clean or replace the plug. Get your runaway RPM issue solved (I still think cleaning the carb will be your best bet)

If it's not too difficult, pull the head and de-carbon it, and that SHOULD take care of the kill switch not doing it's job.

 

Thanks for the reply an input. Brand new cylinder and piston no carbon yet. I was thinking of of the diesel effect also. I did find a ground wire that was running on the bottom of the coil so that may have been getting heat damage. I was thinking the engine was getting hot but it's no hotter then any of my other 2 strokes I run and work on. My daughter rode it today and has not duplicated the problem with her on it.

 

With the coil and CDI being combined, Suzuki wired the kill switches into the wire running from the exciter coil to the CDI/coil. Both switches short this wire to earth, if the kill wires are not plugged into the main wire properly it won't switch off. This doesn't account for a high idle though.

 

I will check all my connections when I get home tomorrow and see if I have any that look weak. I'm thinking the high idle may have something to do with the temperature. I replaced a piece of clear fuel/vacuum line that comes off the cylinder intake fitting for the fuel tank because it melted or started to turn brown thinking it was just cheap part store hose. It just seems like everything is running and idling good now. Would running a cooler plug help on actual temperature of the motor if that was the cause? Let me add this when I did the top end rebuild it was one of the complete kits from ebay.

 

It may very well be heat related. I had a BMW R100 boxer twin many years ago that would start out normal and idle higher and higher as it got warmed up.
Turned out the intake manifold boot (the rubber between the carbs and the heads) had dry rot cracks and as the bike warmed up they expanded and sealed up.
Turned out my "normal idle" was due to a serious vacuum leak, and the "high idle" was more normal condition for where my settings were.
Only after I fixed the vacuum leak and started the bike and it went to 3000 RPM right away that I knew what and where the problem was.

 

I will check for a vacuum leak sometime this week I need to get a pressure tester anyway. It's just funny how a little 50cc has been giving me so many headache and I have a 250 4 stroke that when I rebuilt it didn't give me any problems except for my son going dad turn the key on. )

 

Update we rode for about a hour today and in hasn't duplicated the high idle again. I didn't realize how short I cut the pull cord after a few times it broke. So we installed a new cord and it started right up after a couple of pulls. So hopefully things are taken care of and I can finish making this a running project ATV for my little girl. I just wish the idiot that had before me wouldn't have put his fat butt on it and cracked the frame and then let it rust out. Lucky my partner at the Fire Station is a welder and welded it back for her. Thanks guys for the input and I will give any updates on this issue if it should arise again.

 

If you are anything like me you probably wish you had found something definitive.
I know I would always have in the back of my mind that it MIGHT act up again.
Not to make you worry of course.
On the bright side, being a 50cc, your daughter will outgrow it and most likely won't ever see any trouble with it.

Glad it's running right for you and good luck with it.

 

Yea, I like the knowing whats wrong and the diagnosing portion of repairs. I do like the people who try not diagnosing and just replacing parts till they find the problem. Hey it won't be the first time nor the last time she hits a tree. Thats the good thing about teaching her young is how to respect the trails and machine and not do stupid things.