Bike Not Startting

[Dodgerr]

Hi, my son has a wr125x 2010 bike, he was riding it the other day and it lost power and stopped, now it will not start at all. I have checked for a spark ok, checked it is not seized, the fuel pump primes, I am at a bit of a loss any help would be appreciated.

[Tim W]

Does it have any compression? - if not then may be stuck valve/ broken ring/ holed piston...
Is the plug wet after trying to start it? - if yes then its probably electrical - Try changing the plug - it may spark when you check it but not under compression.
If not you've got a fuel blockage somewhere..

[Dodgerr]

Does it have any compression? - if not then may be stuck valve/ broken ring/ holed piston...
Is the plug wet after trying to start it? - if yes then its probably electrical - Try changing the plug - it may spark when you check it but not under compression.
If not you've got a fuel blockage somewhere..

Thanks for the reply, I have since downloaded a workshop manual, the bike has compression, a spark and I have checked the fuel injection system that seems to be working. I am really at a loss. I am thinking of trying a new ECU unit if not I think i am going to have to pull the engine apart, the bike is only just over 2 years old. It is not showing any faults on the ECU.

[Tim W]

I'd still try a new plug, just to eliminate it..
- try a small amount of fuel directly into the cylinder, plug in and spin it over - if it fires you know you've got a spark and its nothing major..

[thetimkirby]

the bike has compression, a spark and I have checked the fuel injection system that seems to be working. I am really at a loss. I am thinking of trying a new ECU unit if not I think i am going to have to pull the engine apart,

If the engine is turning over OK and has compression, it doesn't sound like a major mechanical problem. Is the compression within spec? Any nasty noises when it broke down? If not, it's more likely to be sparks/fuel.

I'd echo the previous advice: new plug first (cheap), check ignition timing in case something has come loose (unlikely, but worth eliminating, and cheap). Once you are sure the sparks are OK, try the fuel. A squirt of fuel or easy start in the plug hole and try it: no result, it's probably sparks: if it fires, it's probably fuel. Either way, I'd want to eliminate these before going to the time and expense of an engine stripdown.

[Windmill John]

As he was riding it at the time, have you checked all wiring connections and carb/throttle body connections?