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WR250F loses power/bogs when hot?

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Our 2008 WR250F is losing a lot of power after riding it for about 20 minutes. It has plenty of power before that though. The carburator has just been cleaned and jetted properly by our local shop. I've been trying to find information on this issue but most of it has been related to valves and jetting. I know the jetting is good and it starts super easy, so I don't think it's either of those. We checked the spark plug and it was black and wet. Could it be fouled and this is why we are experiencing this? The bike has been unrestricted with Yoshi pipe/grey wire mod but still has the snorkel. Could this be causing our issues? Thanks in advance.

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Is the headlight working? I had this problem once. The regulator rectifier had gone bad but with the headlight working I didn't have a problem. When the buld blew the problem started. Seems that without the headlight the stator produces too much power and caused the bike to misfire if the regulator rectifier isn't working properly. Replaced the bulb, eureka! Then I got a new reg/rec.

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12 minutes ago, DarrellH3 said:

Is the headlight working? I had this problem once. The regulator rectifier had gone bad but with the headlight working I didn't have a problem. When the buld blew the problem started. Seems that without the headlight the stator produces too much power and caused the bike to misfire if the regulator rectifier isn't working properly. Replaced the bulb, eureka! Then I got a new reg/rec.

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The headlight is working fine, but it could be an electrical issue. Is yours an 08 as well?

Edited by Isaachep

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I would check the voltage coming to the coil, cold and compare it to when its hot and running bad. Just unplug the wires where they plug into the coil/sparkplug boot and check with as multimeter. If the numbers are different you will know you have an electrical issue. Now tracking that down is another issue. It could even be the coil. You need to fund someone with th same or similar bike and experiment by swapping parts.

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1 hour ago, DarrellH3 said:

I would check the voltage coming to the coil, cold and compare it to when its hot and running bad. Just unplug the wires where they plug into the coil/sparkplug boot and check with as multimeter. If the numbers are different you will know you have an electrical issue. Now tracking that down is another issue. It could even be the coil. You need to fund someone with th same or similar bike and experiment by swapping parts.

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Thanks so much for the info. I'll go check that later today and let you know what happens.

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2 hours ago, DarrellH3 said:

I would check the voltage coming to the coil, cold and compare it to when its hot and running bad. Just unplug the wires where they plug into the coil/sparkplug boot and check with as multimeter. If the numbers are different you will know you have an electrical issue. Now tracking that down is another issue. It could even be the coil. You need to fund someone with th same or similar bike and experiment by swapping parts.

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There is no way that is going to give any useful information.

The voltage going to the coil is pulsed by the CDI.   This happens too fast for a multimeter to accurately register the voltage.

There may be some static/residual voltage at that connector when the engine is not running but measuring it will tell you

nothing.  

 

If you suspect an electrical issue you should begin by performing  the checks in the Yamaha manual.   Do the coil test cold and hot and

compare the readings.    Have had coils go bad and usually the symptom is severe misfire and poor running versus just going down on

power but definitely a good idea to check the coil and rule it out.    Best scenario is to swap it with a known good one if you have one

available to see if the symptoms change.

 

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2 hours ago, DeepPurplishBlue said:

 

There is no way that is going to give any useful information.

The voltage going to the coil is pulsed by the CDI.   This happens too fast for a multimeter to accurately register the voltage.

There may be some static/residual voltage at that connector when the engine is not running but measuring it will tell you

nothing.  

 

If you suspect an electrical issue you should begin by performing  the checks in the Yamaha manual.   Do the coil test cold and hot and

compare the readings.    Have had coils go bad and usually the symptom is severe misfire and poor running versus just going down on

power but definitely a good idea to check the coil and rule it out.    Best scenario is to swap it with a known good one if you have one

available to see if the symptoms change.

 

I'll try and test the coil soon. I'll let you know how it goes. Thanks.

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This electrical stuff extends far beyond my knowledge. We're going to take it to a shop and have them diagnose the issue for us. But is there anything non electrical we could check before we take it in?

Edited by Isaachep

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