I have a CBR 125 2008 that is used by my sons to ride after CBT and before their main test.
It has been faultless for the past three years and has been well looked after, currently has 24K on the clock but six months ago had the top end rebuilt with new piston Cam chain etc.

Recently we had to keep it outside of the garage for a couple of nights and it rained like hell, on attempting to start it fired but had to keep the throttle wide open to keep ticking over then it died completely and now will not start.
There are no indications of a fault code on the dash, the bike turns over, there is a spark and everything looks ok, if we put a little fuel in the piston it attempts to fire.
Looking at the spark plug we get a spark but its not damp with fuel so suspected a throttle body or fuel pump issue although we get the normal start up with the Fault indicator lighting then going off, fuel pump prime, starter motor engaging on the button and as mentioned a spark.

In an attempt to rectify the situation we have replaced:-

1. The ECM
2. The throttle body, including a new injector and sensors
3. The fuel Pump
4. Used a spare Battery....just in case the current was low
5. Checked all wiring connectors for corrosion etc
6. The spark plug with a proper NGK...again just in case

We are now at a loss as to the problem the bike has done thousands of miles without issue, the engine is good with excellent compression and many new parts.
The side stand, Clutch lever switches and lean sensor all work, their is fuel at the end of the pipe if we switch on the ignition, everything looks ok but we do not see evidence of fuel on the spark plug.
The bike is too good (and an old friend) to sell as parts, we have two members of the family hoping to learn on it, and desperate to get it working again....any help would be appreciated

 

We have now removed the Stator casing and are going to look at Pickup to ECM wiring, in addition as are checking the EHT coil,
I don't suspect either as if we put petrol in the cylinder we get an attempt to fire but going to cover all bases.
To all intensive purposes it looks like the Injector solenoid is not firing but, if we remove the cabling to the injector we see the FI Code that corresponds to an injector failure so looks like the wiring is ok.
I cannot believe that a 125 has such a complex ignition system with so many sensors, its a little overkill for an engine that can only provide 12bhp.

 

Yikes. That's quite a list going so far

If I can make a suggestion, I'd always recommend starting with the very basics before going down the parts spiral. It's a mystery, sure, but a wise mechanic once advised me to always start with the ABC's and rule each one out before going down the rabbit hole. What was the rationale for replacing the ECM? That's usually a big-ticket item. Ditto for the throttle body

Also a few things don't really add up. The bike should be just fine in the rain. There are engineers at Honda who need to make sure that the bike doesn't just die when it gets wet. So unless you see clear signs of a massive electrical fault, it shouldn't really be at the top of your list of prime suspects. We're not ruling out a massive electrical fault, but it's not necessarily where I would start

Fuel
-You had it running, but it was rough, right? Check vacuum system and ensure that all connections and hose clamps are tight
-Suspect fuel strainer. Confirm fuel pump operation (unhook a fuel line and hold a graduated cylinder under it, then prime the pump. If fuel comes out, you're getting fuel to the injectors). If no gas, suspect strainer, pump relay, or fuel pump. Troubleshoot as required (start with the strainer as it's the cheapest and can be cleaned with solvent and compressed air). You've already replaced the fuel pump, but it'd be worthwhile to check the relay as well
-You replaced the injectors, but did the old ones have evidence of gumming or other contamination? It didn't seem to make a difference, so it's moot. Keep 'em for spares
-Put fresh gas in it, especially if it's been stored
-From what you describe, fuel is definitely a prime suspect, especially if the plugs are dry

Electrical
-Ignition system is also a prime suspect at this point. It sounds like you've confirmed spark, and if so, it should be ruled out. If not, recheck spark. Troubleshoot as required
-Check all fuses. Use a multimeter. If you had a massive electrical fault, there's a small chance that a fuse has 'fused' where the terminals have melted together and instead of severing the circuit, if so, it would potentially allow a large current to damage an electrical component. It's not likely, but it's possible. What's more likely is that a fuse has blown, and electricity is not able to access the starting or ignition circuit
-You say you checked the wiring. Did you see any signs of melted plastic or burned insulation? If something melted, you'd be able to see it - especially if it's on the starting or ignition circuit. Make sure to check the common grounds if you haven't already
-With fuses and harness visually inspected, connect a fresh battery or booster pack and attempt fire
-If no change (still ticking noise) try jumping the starter to confirm that it is operational
-If it's not the starter or the fuse or the battery, we can move up to the controls. These can be damaged by weather, but it's usually an old bike problem so not something you'd expect on an '08. Verify switch operation using continuity function on your multimeter
-Since you've already got the multimeter out, the next step would be to confirm side-stand switch and neutral switch (if equipped). It sounds like you've already checked these, but it's worth double-checking as they would stop the bike from starting
-If nothing works, confirm theft deterrent system isn't the issue (if equipped)

Engine
-It sounds like a lot of mechanical work has been done on the engine already. I'd be remiss if I didn't recommend popping the valve cover off and turning it by hand to confirm timing. A sudden timing belt failure would definitely stop it from running, but you'd also have other clues that would point in that direction. Has it been modified?

Hope that helps

 

what tentacleslap says....