WR250R stopped running and won't start

I was riding home on a fairly hot day the tank was on reserve but there was still about 1/2 gallon in it, (I know cause I filled it up thinking I had run out of gas), I was full out going up a slight grade at around 4,000 RPM, when it felt like the bike was seizing up it was starting to slow down like it was turned off, I shifted down to get the RPM up and it kept running. I slowed down to go around a corner and it died and wouldn't start. I filled it up with gas and it still wouldn't start.

I took off the tank and injectors and gas squirts out when you crank it. I pulled the plug out and held it against the frame and there is spark, (maybe weak how do you know>. I put in a new plug. I checked the primary and secondary coil resistances. I tested the Angle Sensor which worked backwards from the book but must be okay. I looked everywhere for a loose connection (especially the places where others had problems), I checked the airbox and the pipe for obstructions.

I'll try and check the stator tonight, and check the timing??, valves?? Compression???.

I bypassed the FMF controller, same thing.

So it cranks but nothing is happening it doesn't sound like it wants to start at all. I have it on a battery tender. I know others have said they can be finicky about getting enough voltage, but I should be okay if the battery is cranking the engine??

Any ideas or thoughts on what I should try next. Bike is 08, with FMF pipe and controller, Thumper Racing Big Bore kit, kickstand switch disabled, front and rear light mods. All mods done by someone else so I don't know anything about them.

Do you hear the fuel pump priming? 08's are notorious for having fuel pump failures.

Fuel pump is priming andgas squirts out the injector when I try to start it.

A few ideas:

battery - could have lost a cell and not have enough voltage, try jump start

diagnostic mode - run through the tests and check if any codes are stored, at least one test will show voltage (12V from battery)

check/workout the engine kill switch - perhaps even spray it with wd40

try starting it with full throttle

service the air filter

check the ecu . Try to borrow one from someone who has same bike,sounds like the culprit/////

if you have good battery spark and fuel then the only things you are missing are air and COMPRESSION check compression and if it is low i would move on to timing and valves if the ecu was bad i see you having a no spark issue. as far as the kick stand switch mod goes and the tip over you would not have fuel or spark. (one or the other i am guessing i would have to check the manual or test on my own bike) so that should be fine. if it died all of a sudden like you said it sounds like a lean running or overheating issue but im assuming the overheat light was not on. i would start with compression like i said and move on to timing and valves if that is low. another thing, might me low fuel pressure just because it is getting fuel does not mean it is getting the right amount of pressure to atomize fuel correctly to start.

I had a ECU go bad on a Suzuki 4-wheeler and I had good spark at spark plug but would not start just a maybe//

Thanks for the ideas. I got an ignition spark gap tester and all tests good, so I'm thinking it can't be an electrical issue. Will do compression test tonight if I can get a tester.
Oh I also did try with full throttle. I will look up how to do diagnostic mode and see if there is any info.

Compression test failed. 30psi then 90psi with a tbs of oil dumped in the cylinder. This bike has the Thumper Big Bore kit installed and a total of 1,800 miles. Not Happy. Take the cylinder off tonight.

gotta love pancake pistons with one compression ring been there done that on my 450.

sure it will run like a bat out of hell but they do not last!!!!! that sucks man

Took of the cylinder and all three rings are welded into thier grooves on the front of the piston. The cylinder wall is gouged also. Gotta figure out why and if I should buy another Thumper kit or go back to stock or Athena. Anyone else had these Thumper Racing kits fail.

sounds like a lean seize what fuel controller are you running and do you warm the bike up or just get on it and hit the road. not warming the bike up usually caused a 4 corner seize but can also just score on the exhaust side of the piston only. i would be looking more for a lean condition since just jumping on it without warming it up unless you run the holy hell out of it cold over and over is probably not likely. i would say the piston to cylinder clearance was wrong but i didnt measure it number one and number two you would have an even seize all the way around the piston. so in my opinion and mind you i have not looked at it this is speculation with very few details you need more fuel!!!!

I'm running the FMF programmer, full FMFQ4 pipe, opened airbox. No idea what the programmer was set to. The bike was supposedly built as the demo bike by Thumper Racing to show off the new big bore kit. I bought used. I always warm up the bike and it was at the end of a long ride at near full throttle that it stopped. Just ordered all new stock parts $434.00 at onlinecycleparts and will let you all know how it goes, plus I will check the FMF programmer settings before I get it up and running.

I haven't found a single report from anyone that says they've gotten 10,000 or more miles out of one of the big bore kits and I really like to ride not order and replace parts.

With only 1800 miles, even if it wouldn't do any good, I'd be letting Thumper racing know their engine is a POS.

yeah i understand your frustration hope you get it up and running soon