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Discussion Starter · #1 · (Edited)
Hi, as in title i have problem with cold starts, one time it fires well and one time it's just shut down and i can not help it with a little rev (with a rev check engine blinks and bike slowly shut down) after that it runs well. Does anyone have any idea?

EDIT: title
 

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2008 YZF-R125 (180cc)
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if it runs ok once it's wam it sounds like maybe something to do with the warm-up enrichment (equivalent to having a choke), which as far as I'm aware depends largely on the temp sensor.

so maybe check the temp sensor on the right by the thermostat. I'm pretty sure the service manual (from a gen1 will do if yours is later) shows how to test it.
 

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Discussion Starter · #3 ·
if it runs ok once it's wam it sounds like maybe something to do with the warm-up enrichment (equivalent to having a choke), which as far as I'm aware depends largely on the temp sensor.

so maybe check the temp sensor on the right by the thermostat. I'm pretty sure the service manual (from a gen1 will do if yours is later) shows how to test it.
I tried to pump fuel twice at the start and it started well, warm-up went well. I got another fuel pump so I can replace current pump and see if that will help. What do you think?
 

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Discussion Starter · #5 ·
a little update, now cold start goes well - warm-up around 2k rpm and its good to go but after ride and letting it stand for 10-30min it have rough time on idle - tries to keep 1.4-1.5k rpm but it sound like lack of spark or fuel what comes to shut down (if i won't rev a little for a while)

haven't checked fuel pump, temp sensor and spark plug yet (will do as soon as possible)
 

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2008 YZF-R125 (180cc)
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so based on what you've said it's a little out but at the hot end, plus there's the accuracy of the thermometer etc to account for so Idon't see a little variation there as being a major issue. When you're starting up it'll be at the 20deg end which seems to be pretty much reading in spec.

Well I guess it's probably not that then.

just out of curiosity what are your battery voltages? i.e.voltage across the terminals with the engine off, and with it running.

hmm :unsure:
 

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2008 YZF-R125 (180cc)
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ok so battery seems fine.so it's not lack of power from a dodgy cell or some nonsense like that..

hmm. Did you check fuel pressure or replace the fuel pump? It may not be that but I'd be tempted to put a new one on just to rule it out.

pls bear in mind it's also extra difficult trying to diagnose this stuff without ever having seen/heard the bike do its thing...

what year is it pls? I thought you'd mentioned but I can't see it (or am missing it)
 

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Discussion Starter · #11 ·
I was going to but i coudn't find fuel pump that i ordered some time ago becouse i needed fuel meter - somebody threw it out, im going to order another one.
Yamaha r125 2014
I know it's not easy and im glad that you are willing to help me.
I found a post about similar problem like mine - Problem With Starting When Warm
 

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2008 YZF-R125 (180cc)
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ah right - so they also seemed to think it was the fuel pump. That's encouraging. I think the 2014/gen2 fuel pump is removed a little differently from gen1.. the big plastic ring has 6 allen bolts holding the ring in place instead of a giant threaded ring I think, potentially a better system and should be easier to remove.

But for £20 or whatever a pump[ costs that would probably be the next thing I'd want to try and rule out.
 

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Discussion Starter · #13 ·
Hi, im back
Sooo my bike was resting a little (around 2 weeks) and it would not start with starter but runned by starting on gear.
I check some things and fuel injector was running not as it should - it poured drops of fuel and it give right sound (click) but now any gasoline wont get through can it be cleaned or i have to buy a new one?
And I changed fuel pump for a new one
 

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Discussion Starter · #14 ·
I cleaned fuel injector and it runs but after that and replacing fuel pump for a new one problem didn't vanished - still the same (rough time starting on warm engine after 10-15min off)
 
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