KX85 cutting out when hot?

Loftin79
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Loftin79
A buddy has a KX85 and it runs fine up until its ride for a bit and gets hot, then it cuts out and sputters. Let it sit and cook down then it will run fine again til hot. Any ideas what it could be? Thank you
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hillbilly
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hillbilly 7/10/2016 11:16am
7/10/2016 11:16am
Loftin79 wrote:
A buddy has a KX85 and it runs fine up until its ride for a bit and gets hot, then it cuts out and sputters. Let...
A buddy has a KX85 and it runs fine up until its ride for a bit and gets hot, then it cuts out and sputters. Let it sit and cook down then it will run fine again til hot. Any ideas what it could be? Thank you
Put a new sparkplug in for sure,

Make sure coolant is full.

Drain the carb bowl. Cant recall if it has a drain screw on that model. If not just loosen the cap on the bottom of the carb and let fuel drain out in case there is some water in the bottom.

If he already has installed a new plug take it out and look at the color. If it is dark brown/black then it is going rich for some reason. A light color be lean. Both will make it misfire.

The filter has been cleaned right? When trying to diagnose a problem you never know how well the bike is maintained so it throws a lot of variables in.
kzizok
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kzizok 7/10/2016 11:30am
7/10/2016 11:30am
Loftin79 wrote:
A buddy has a KX85 and it runs fine up until its ride for a bit and gets hot, then it cuts out and sputters. Let...
A buddy has a KX85 and it runs fine up until its ride for a bit and gets hot, then it cuts out and sputters. Let it sit and cook down then it will run fine again til hot. Any ideas what it could be? Thank you
Thats it. Pretty classic with KX85 presentation.
ga_pike
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ga_pike 7/10/2016 11:31am
7/10/2016 11:31am
Loftin79 wrote:
A buddy has a KX85 and it runs fine up until its ride for a bit and gets hot, then it cuts out and sputters. Let...
A buddy has a KX85 and it runs fine up until its ride for a bit and gets hot, then it cuts out and sputters. Let it sit and cook down then it will run fine again til hot. Any ideas what it could be? Thank you
This. Had a similar problem on my RM 80 back in 1989. Eventually found the plastic cover would warp slightly and let water in, ruining the stator. It would be great until it warmed up and then run like crap.

The Shop

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scott_nz
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scott_nz 7/10/2016 11:43am
7/10/2016 11:43am
I have seen coils go as well, and when they do they miss in high rpm when hot,

best way to sort out is if you can get another bike and swap parts over, to try to get the other bike to do it,

Cygnus
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Cygnus 7/10/2016 11:52am
7/10/2016 11:52am
I would have to go with stator too.
kzizok
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kzizok 7/10/2016 12:05pm
7/10/2016 12:05pm Edited Date/Time 7/10/2016 12:05pm
We ran them fairly recently, for quite some time. Good news is, it isnt too common (unlike the Nikasil flaking).
langhammx
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langhammx 7/10/2016 12:43pm
7/10/2016 12:43pm
Loftin79 wrote:
A buddy has a KX85 and it runs fine up until its ride for a bit and gets hot, then it cuts out and sputters. Let...
A buddy has a KX85 and it runs fine up until its ride for a bit and gets hot, then it cuts out and sputters. Let it sit and cook down then it will run fine again til hot. Any ideas what it could be? Thank you
kzizok wrote:
Thats it. Pretty classic with KX85 presentation.
^^^ THIS ^^^
More than likely !!
Uncle Tony
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Uncle Tony 7/10/2016 4:24pm
7/10/2016 4:24pm Edited Date/Time 7/10/2016 4:25pm
Loftin79 wrote:
A buddy has a KX85 and it runs fine up until its ride for a bit and gets hot, then it cuts out and sputters. Let...
A buddy has a KX85 and it runs fine up until its ride for a bit and gets hot, then it cuts out and sputters. Let it sit and cook down then it will run fine again til hot. Any ideas what it could be? Thank you
kzizok wrote:
Thats it. Pretty classic with KX85 presentation.
langhammx wrote:
^^^ THIS ^^^
More than likely !!
Yup got to agree, got to take the cover off now and then especially if dad is pressure washing the Shiite out of it, let it breathe my son but the damage is done
Beast666
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Beast666 7/10/2016 4:25pm
7/10/2016 4:25pm
Stator or CDI box breaking down with temperature.
bsharkey
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bsharkey 7/10/2016 5:34pm
7/10/2016 5:34pm
got to love those stators. especially on cobra 50s
hillbilly
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hillbilly 7/10/2016 6:58pm
7/10/2016 6:58pm
Well maintained bike then yeah a stator could be it.

If the plug is old ,the filter 5 lbs of dirt on it and the oil never changed it could be simple and cheap.

Definitely pull the flywheel cover,if it is wet that's the problem most likely. Wd40 and airhose it out.
Loftin79
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Loftin79 7/10/2016 7:08pm
7/10/2016 7:08pm
Thanks for the help guys. I know the filter is cleaned, he maintains it pretty well. He will be checking stator it sounds like

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