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2003 yfz CDI problem?

G

g0lazooo

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Mar 20, 2025
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trying to bring back an old 2003 yfz with a really interesting issue. It dies after running for a few minutes then it wont start again for a bit. replaced and adjusted almost everything like its, jets, carbs, sensors and a few more, still no imrpovements. Same thing happens everytime. im now thinking maybe CDI or a worn exhaust valve bucket is where the issue is.
 
wow that is REALLY INTERESTING and sounds really frustrating. like that you did the preliminaries and gone through the carbs, jets, sensors (these are essential). yes you should check the CDI right now because this may be related to heat-related cutouts. and yes you may have a worn exhaust valve bucket since this f's up the compression after warming up. hope you get it sorted soon. try test sparking immediately after it dies to check if it must be something to do with your ignition.
 
g0lazooo said:
trying to bring back an old 2003 yfz with a really interesting issue. It dies after running for a few minutes then it wont start again for a bit. replaced and adjusted almost everything like its, jets, carbs, sensors and a few more, still no imrpovements. Same thing happens everytime. im now thinking maybe CDI or a worn exhaust valve bucket is where the issue is.
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you have to do many things to bring back an old motorcycle to life. How long did you keep it untouched? you probably need to replace the fuel if it has been too long. check if there are missing parts, check for compression, and many more
 
Have you managed to resolve this? my brother's bike is also experiencing the same issue. Maybe we should check the exhaust
 
g0lazooo said:
trying to bring back an old 2003 yfz with a really interesting issue. It dies after running for a few minutes then it wont start again for a bit. replaced and adjusted almost everything like its, jets, carbs, sensors and a few more, still no imrpovements. Same thing happens everytime. im now thinking maybe CDI or a worn exhaust valve bucket is where the issue is.
Click to expand...
It's a classic heat-related CDI failure to me, especially if it restarts after cooling down. But yeah, definitely worth checking valve clearance too, those buckets can cause all kinds of weird issues when worn.
 
CDI or stator issues, heat kills spark, cools down, starts again but tight exhaust valves can do the same, so check valve lash and compression cold first. If that's solid, try a known good CDI
 
I had the same weird thing happen with my uncle's old quad. It started up fine when cold, but then it would sputter and die on every ride. We messed around with the carbs for ages, but then a friend let us borrow a spare CDI unit. We swapped it out, and bam! Problem solved. You should check that out first before you start tearing into the engine.
 
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No one thought to point a finger at the fuel pump? If it's failing it could be overheating and shutting down. Once it cools off it could run again fine for a few minutes.
 

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