New to this site and looking for some help.
Recently I've been having troubles with my 2015 KX250F regarding it starting. When I bought it (used) a few months ago it started on the kick like normal and ran like a dream. Not even a month into owning it, the thing would not start cold on the kick no matter how long I spent flogging it; it could only be started by rolling it. However once the bike was warm, it would start 1st or 2nd kick no problem.
Now recently the bike will not start whatsoever. Tried to roll start it and it kept a big sort of buzz but never really caught on and started. I put a new spark plug in and cleaned the air filter but no luck. It is fuel injected so I feel it may be a problem with that. My mate suggested I could need to dump the fuel and put fresh fuel in but just looking for other possibilities.
Check your valves. Probly unlikely but could be a clogged injector.
First suspect would be the valves.
When I bought the bike I was told "it just recently had new rings and valves". Possible it was done incorrectly?
They probably just need to be shimmed. A symptom of bad valve tolerances is hard starting, then eventually wont start at all. Also odd they said they replaced the rings but they were too cheap to replace the piston too. Not sure why you would go through all that trouble to get to the piston, then just to do the rings. I would check compression too.
As Rockinar said. As the engine wears, the valve clearances get tighter. Eventually it causes operating problems and usually in the form of being inconsistent at starting it. This is perfectly normal and happens to every bike eventually.
You should check your cam to bucket valve clearances. Adjust (shim) them as necessary to get back in specifications window for the gap. It is not hard to do; a little web research and a couple of youtube videos you should be in good shape.
A bad batch of fuel is possible. Easy to dump the take and try fresh.
A new spark plug surprisingly makes quite an improvement too.
I doubt it is the piston job. If it was done incorrectly, it would have quit before you able to ride it much.
1. Fresh fuel and clean lines to the injector.
Let us know how you make out. If those don't fix it, then we can get into the injector and stator type stuff.
PS: check that all wiring plugs are well connected and not loose somewhere.