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Yzf R125 turns over but won’t start

194 Views 1 Reply 2 Participants Last post by  NorthCust
Hello everyone!
I’ve got a Yzf R125 with the white dial (not sure of the age as I’ve got no license plate)

I bought the bike along with a few others as a job lot from Co-Part.

the bike has been laid down at some point, the frame is straight but quite a bit of cosmetic damage.

I have put a battery on it and everything lights up, start motor turns over but it won’t catch.
I’ve checked the fuses and they’re all good.
I’ve checked the “tip over” sensor and unplugged it and put it back.
I’ve checked for spark and it has spark. I’ve drained the tank and put fresh petrol in it.
I have applied some easy start to the intake and tried starting it. On this occasion it managed a single pop until the battery died.

any suggestions on what I could try next?
Thank you
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is there any evidence of fuel on the spark plug when you take it out to check? e.g. is it wet, is there actually fuel getting to the cylinder?

Maybe worth checking the injector/fuel pump is working if you're not sure. Taking injector out and having it squirt into a jar would confirm it's working. If you find there's no fuel pressure, testing the fuel pump is easy - just take the hose off and it'll shoot a jet of petrol straight up if it's working - likely as soon as you turn the key, and then again/more if you hit start.. Mind your eyes and obvs don't do it indoors/next to an open fire.

Also - compression. If you try turning it over by hand can you feel compression? turn over using a socket in the central hole on the stator side, turn anti-clockwise.

If it has fuel, air, spark and isn't firing then I would probably be looking at compression next. Due to the teeny tiny spark plug hole getting a compression tester in there is quite difficult so gauging it by hand may be the only option. The compression ought to be quite firm and noticeable at first and would fade slowly (e.g. if you turn it really slow) but you should really be able to feel it sealing. If that resistance isn't there that could be the issue.

If the motor turns over really easily on the starter (vs you can hear it having to work to do the compression) that could be another clue towards it being low.

hope that helps..
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