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07 WR450 dies at idle after its warmed up

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Hi Everyone,

In a last ditch effort I'd want to see if any of you can help me out. I have a 07 uncorked WR450 that starts easy. But after it's been run around the block a few times and is good and warm, it sputters and dies at idle which is around 2000-2100 right now. I have to keep revving the throttle to keep it alive when I come to a stop. It has been to 2 different shops, had the valves adjusted, they pulled the top half of the motor and inspected, pulled and cleaned the carb, and it still has the same issue! I've lost faith in the shops to fix it and haven't found any solution online that has worked so far, so I was hoping someone could help me out. I have a 168 main and a 45 pilot. I run at sea level in moderate temps.

So far I've:

  • Verified fuel flow from the tank to the carb
  • Pulled and inspected/cleaned the carb and jets
  • Made sure the battery was charged
  • Checked valve clearances (shop done)
  • Pulled the top half and inspected (shop done)
  • Inspected and adjusted fuel mix screw
  • Replaced hot start cap with an aluminum one in case of leaking
  • Inspected for air leaks

If anyone can point me in the right direction I'd be super excited on getting this thing running reliably! Thanks.

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Have you tried squirting easy-start or brake cleaner into the airbox as it dies? If the revs pick up you can be sure its fuel starved. If it still dies, it's something else. Could be the Coil, plug cap, trigger or CDI breaking down under heat. Do you have a strong, bright spark when the bike is hot?

 

EDIT

When you cleaned the carb did you split the upper float bowl? When i bought my '07 it had been parked up for 4 years. Ran very poorly/hot at idle. Gave the carb a quick clean - no improvement. Split the upper bowl and replaced the swollen o rings. Massive improvement. Idles perfectly and very hard to stall when riding

Edited by Pancho_Jsy

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Please do not spray solvents inside the carb bell!  Products like Easy-start will melt the slide plate seal inside the FCR carb.....and make all the rubber parts inside the carb swell, permanently.....

You are loosing fuel or spark.

It sounds like you have elminated fuel.

Why the shops have not performed the typical Stator tests, is hard to understand. The tests are in the OEM serviced manual.

Most likely, you have a dying stator.

If the bike ran for any signifigant amount of time with the stock set up (runs extremely hot) then the stator is fried from heat.

 

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Thanks for the advice! I took a look at the stator hoping to see it fried, but it looks good as new. It appears to have had the mods done to it prescribed by the Baja Designs dual sport kit. I forgot to mention that the bike has this kit installed. 

I also performed the stator resistance checks per the manual and per the Baja Designs kit and they seemed to pass (when the bike is off). I was unable to figure out or find ways to test the coil, rectifier, or CDI while the motor is on to verify voltages, etc. I think the motor needs these connected to run and the connectors are all sealed so I can't probe while connected.

Could anyone suggest a link or a how-to on performing additional tests? Are there any other suspects? I don't see how a CDI can breakdown after some on-time unless it's receiving direct high voltage from the stator and is self-heating. 

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Just meter the battery leads with the bike running at ~2500 rpm.. you should see a noticeable power increase (~14 VDC) versus just the battery voltage and motor not running.

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Did it ever run correctly with this setup or did you "uncork it" and now it has this problem?  It could be lean and need a larger pilot or richen the air fuel screw.

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It seems like it was indeed the ignition coil. It's wild that after multiple trips to the shop they didn't figure this out... After swapping with my friend's ignition coil there was immediate improvement. It was idling at 1800rpm no problem and no stalling after a long ride! Thanks for everyone's advice!

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