2007 yz450 won't start after warned up?

Any luck on this bike?

One thing to keep in mind is that you may be able to see a light spark with the plug removed, but when in the cylinder under compression the spark will not be as good.  Since you have tried starting fluid, I am betting you are some how getting a weak spark. Which could keep a hot bike running but may not fire up by kicking it.  No hills nearby to try rolling it off.  Try 3'rd gear to get the engine turning over.

No luck boys!!!!!! :/

I took the carb clear down....split it and everything!!! Took it to my guys at yamaha and hit the sonic for a couple hours!!! Got it back, put it together and installed....

Fired right up....ran it hard...WONT START!!!!!

I pulled the tank right away...pulled the plug....seems dry!!!!!! But also can't seem to get it to spark!!!!! I even held the dam thing....grounding it and kicking....wldnt zap me.....

After it cooled down....tried zappin myself again and nothin.....put the plug back in and it started!!!!!!!

Haha. I have no idea!!!!

It's gonna go in pieces shortly.....

I'm gonna try a hill tomorrow....

What wld cause weak spark!!??

Re-read the post and no mention of a new spark plug....I would try a brand new one just in case.

 

If that doesn't work, i would try to hot start with a new/cold plug installed.

had a bike do this to me once. my problem was the coil once it got hot it would quit throwing good spark.

Sorry guys....I thought that I had mention the coil...

I have switched it out while hot with another bike I have and it still wouldn't start!!!

It's gotta be spark somehow....

Will the neutral switch on the shift drum make it not start?? I noticed those wires have been hot from the head pipe....that's THEE only electrical I haven't tried switching....

Sorry guys....I thought that I had mention the coil...

I have switched it out while hot with another bike I have and it still wouldn't start!!!

It's gotta be spark somehow....

Will the neutral switch on the shift drum make it not start?? I noticed those wires have been hot from the head pipe....that's THEE only electrical I haven't tried switching....

 

It will run just fine without it. Unplug it and give it a try but it should not matter. I cut mine flush with the sensor just to avoid snagging it and breaking the plastic causing an oil leak.

The neutral switch can be tested easily.  Disconnect the lead from the harness and read continuity from the connector, through the lead and switch to ground. The lead should be grounded in neutral, but nowhere else. 

 

If the lead grounds in gear, the rev limit will be lower (about 7000) than normal, and the timing curve is different.  But either way, it shouldn't keep the bike from running. 

Had a snowmobile with the exact same issue. The name if the part slips my mind but it was something to do with a voltage regulator.

Edited by bradgross71

I think it came down to too much voltage getting to coil making it to hot to work properly.

There is no current regulator in the YZ450 electrical system.

This is starting to look like a flaky CDI box, but those rarely fail.

A mystery and no mistake. Apparently another (presumably known good) CDI has already been tried.

 

What baffles me is that it just won't start, rather than, dies when hot. I think I'd still be trying to measure voltage outputs while running and watch how they behave as the temperature rises, Learned the hard way by taking my SWM all the way to Scotland for a speed hill climb at Doune. First run it got halfway then died. Got back down and it started. Did the next run on a cold engine kicking it up after pushing to the start line and still only got 2/3rds of the way.

 

Then someone in the paddock produced a multimeter and we hooked it up to the stator winding. Sure enough the voltage cold was X but dropped as it warmed up before finally rapidly cutting to zero. From then on I carried a spare rewound item (Bosch originally). What made it worse was that as it died it seemed to put the timing out. Not too bad on a hill but when I was circuit racing it I'm pretty sure it was responsible for a couple of piston meltdowns (air cooled 2T).

 

Yet the stator is new. I've had old Morinis with rotors needing re-magnetising and difficult to start - though usually in conjunction with poor winding resistence, but how about a long shot?

http://www.physlink.com/education/askexperts/ae472.cfm

my friends 2004 rmz250 did this to, he replaced the valves, re-jetted the carb and put new rings in it, and nothing helped, eventually it just blew up without reason, and he sold it for 500 bucks :/

Looking through my manual today and a part is listed as a rectifier/regulator.

Any solution as of now? Mine started to do the same thing last week after replacing a stator with an open across one of the coils. Everything on mine ohms out in spec, ground is good, and I have good continuity throughout the wiring harness. Crazy thing is, you can ground the (new) plug against the head and not see any spark at all, even cold. Install the plug, kick, and it fires up. Let it get a good heat soak from riding and it won't kick start to save my life. It'll bump start fine though and run great once it's going. Jetting was spot on before stator replacement.

im having the exact same issue with an 09 yz450f.....there has to be some sort of an answer....anyone? BUELLER? BUELLER?

It has to be valve/tappet issues?

nope...brand new valves with seats recut....yz450f's dont have tappets...

Sorry guys!!!

It was the stator on my bike!! Oem original went bad....Wld start then heat up and lose contact!!!

Replaced it with an aftermarket stator, same thing!!!! Ohms were high...

Put a brand new oem stator in and it fixed it all!!!!

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