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Guys, maybe somebody has experienced this. My 2018 CRF250R stalled on the track yesterday and will not start again. Have changed plug, unplugged kill switch, even changed the vortex box back to standard. It refuses to start even when I spray starting fluid directly into air intake.
Could it be a timing issue?
Its driving me crazy !

A little more background would help .... how many hours on the bike ?? , did you just pressure wash it ?? , what did the plug look like ??? , and most importantly , do you have a manual , so you can perform fuel and ignition tests ?? , depending on the hours , did you check the valves ?? , a simple check of the timing plugs will tell you if its in time (cam sprocket marks , plug on ignition side and clutch side all need to be aligned , if they are , then it's not timing)

Usually when the new gen bikes won't run its the kill switch that got water in it (yea a dirt bike you can't get wet , smart right ??) , but you said you disconnected it (not sure on the new gen if the bike will run with the kill switch disconnected since it is also a MAP switch) , does it crank over at normal speeds or is it slow cranking ?? , also , when it cranks over do the lights flash on the kill/map switch ?? , if so what is the sequence and/or how many times ??

Possible causes are Fuel Pump or Fuel Filter , Kill Switch got wet ,, Ignition connector got wet , bad engine Ground , Fuse Blown ...... Those would be my first guesses ....

Bike has run 48 hours in total. The plug had a weak orange spark, but did a test with the new one and it was a nice strong blue one. Still wouldn't start though. Bike was pressure washed 4 days ago so cannot be that either. It run 3 laps before it stalled.
The light stays on for 2 seconds and then goes out so all is good according to book.
It's due a new piston and cam chain anyway so I will pull out the engine and clean all contacts properly and check timing.

I would not pull the engine apart until you found and fixed what is stopping it from running. Adding other variables to a non-running engine could really complicate things.
I suspect you got water into something. Pressure washing can do that.

I agree with Neil , wait on teardown till you solve this issue ... and just because the MAP light is not giving a error does not mean the switch is not grounding out because of moisture inside it ...... , basically condensation leftover from the pressure wash (again , another known issue), so the moisture stays till it's removed and it can move around in there and ground out , then not ....

Also , have you tried bump starting it (get it going , preferably on a slight grade and stick it in 2nd or 3rd and dump the clutch) , see if it starts then , some people have had a issue where it ran fine , then would not start , then they bump started it , and it started fine afterwards , not sure the reason , but it is a known issue/solution ...... sometimes .......

Also , how is the engine cranking over ?? , fast or kind of sluggish ?? , the OEM batteries are known not to be all that great , it could have a weak or bad cell

If the battery is not up to scratch it can still crank fast enough to start an old carby engine but not have sufficient voltage to allow the electronics of a modern engine to run.
Since you got good spark after changing the plug I would recheck that to reconfirm spark is still ok.
If that is the case you would have to think a fuel or low compression issue.
Try a bit of starting fluid as a quick test as an example.

Good luck and don't pull it down to you have diagnosed the problem.

The engine cranks well (better with choke on) and I used an extra battery with jump cables as mine had died after all trying to start it for a long time. It feels like it's just about to start but never does. I have sprayed starter fuel directly into intake and that didn't do it either. I have also disconnected the kill switch and that didn't do it either.
But you are right, I will not pull engine out until I have got it started again

OK , the engine needs Fuel , Air , Spark , Timing , Valves Set , to run , you need to eliminate each one , first things first , take the plug out , dip it in gas, and put it right back in , and try to start it , if it fires or attempts to , your issue is fuel related , it could be a clogged or bad Injector , or the Fuel Pump , starting fluid may not start it if it is not getting any gas whatsoever ...... Next if that fails to prove anything , is Spark , you need to test the Coil output/resistance , this will tell you if the coil is working , or failing under a load , check the Stator output ......If all checks out ..... Next check Valves and at the same time check the Timing , if a intake is zeroed out (unlikely with a bike this new unless you got a ton of dirt past the air filter) it will cause it not to start .... The fact that you mention it tries more with the choke leads me to believe its fuel or valve related ,as it may be getting too much air via a open/worn valve , or as mentioned a clogged injector or weak fuel pump ....

Well, after checking everything externally ( even measured valve gaps and checked timing markings ) decided to open up the engine.
And there it was in all it's glory: a cracked piston
Amazing, considering there was a lot of compression but just happy to have finally found the fault

Wow !! ...... Well that was unexpected ......

Interesting how a stall resulted in a cracked piston or a cracked piston resulted in a stall. Probably lucky it did stop though.
Can you post a few pictures of it?
You really need to work out why it cracked.

Well, I am using a Vortex box and friends are telling me that it could be the culprit. Engine was also ported and flowed and run on a dyno with yoshimura exhaust system, by a reputable modifier. It is now in with a wiseco piston and new cam chain and runs beautiful. Trying to upload a photo of the cracked piston but it says it's too large even though it's only 260kb

Well, I am using a Vortex box and friends are telling me that it could be the culprit. Engine was also ported and flowed and run on a dyno with yoshimura exhaust system, by a reputable modifier. It is now in with a wiseco piston and new cam chain and runs beautiful. Trying to upload a photo of the cracked piston but it says it's too large even though it's only 260kb

When your bike did this, did it gradually die or just flat out stop? And did it start back up at all or not once? My 19 has the same mods as yours minus porting and it did this to me today. Already had the issue with the kill switch, that's fixed and it doesn't change when it's disconnected. My bike died, wanted to start back up and then wouldn't stay running. After going back to the pits it would start, not easily, and wouldn't stay running without staying on the throttle.
Just before I left the track, the battery sounded like it was done. I have an extra battery at home I'm going to try but I'm still fearing the worst, ie piston cracked or it's about to sieze. But if it were I would think it wouldn't have wanted to fire back up at all? So hoping it's just the battery

Well, I am using a Vortex box and friends are telling me that it could be the culprit. Engine was also ported and flowed and run on a dyno with yoshimura exhaust system, by a reputable modifier. It is now in with a wiseco piston and new cam chain and runs beautiful. Trying to upload a photo of the cracked piston but it says it's too large even though it's only 260kb

You need a Hosting Site to upload a pic , like IMGUR or similar , you post a link to the image like this
[img]https:/ /i.imgur.com/PaWWmGG.jpg?1[/img] directly into your post just like I did here

And it shows up like this ... Well ...... the guy in your pic won't look this good , but you get the idea ...