'06 YZ450F Intermittent Hot Star Failure, Help!

2006 YZ450F, 5 hours since new piston, rings, timing chain, valve re-shim, new plug, and general cleaning and lubrication of all moving parts (suspension). Has a "Power Now" and Rekluse.

Bike runs like a raped ape, awesome power, smooth idle. Will hot start with ease most of the time. However, twice now I have killed the engine via the kill switch and it has failed to restart until it cools for approx 1 hour. It never did this to me last year, happened on the second and third ride since the major maintenance I performed this last winter.

Troubleshooting steps taken:

1) Kill switch is operating correctly, no faults found.

2) Valve clearances, checked yesterday, well within tolerances (checked cold)

3) Primary and secondary coil resistance within tolerances. (checked cold)

4) Spark plug is clean, mixture appears to be OK. Have changed plugs on the trail, didn't help.

5) On the trail, we pulled the plug, kicked the engine over, and could NOT detect the spark.

6) Hot Start plunger is definitely actuating, and doesn't appear to be sticking or leaking.

When it decides to pull this shit on me it doesn't even try to start. No pop, no cough, nothing. This makes me think its ignition. When I was checking the coil resistance I noticed a little oil residue and crud on the connector. I cleaned it thoroughly with electro cleaner. I pulled the bike out yesterday in the 90 degree weather and ran it for 45 minutes at high idle. I stopped and restarted every 15 minutes without a failure.

Any ideas? I have a feeling I'm going to need to take additional tools to troubleshoot the bike when it fails on the trail again. It's a little embarrassing and rude to the other ridesr to constantly hold them back from an otherwise fun ride.

Thanks for the help.


Test the stator as described in the manual. If you can't find any anomalies when you test, pack the VOM with you and try it when it decides not to work.

I checked all 3 coils in the stator. The manual asks that you perform these checks at 68 degrees. The garage was about 95 at the time, so I can expect the resistances to be a bit on the high side.

1) Pickup coil good.

2) Source coil 2 good.

3) Source coil 1 was a little out of tolerance. Range is 720 to 1080 ohms. I got 1200 ohms.

Yes, its high but not by much considering it was 95 degrees in the garage. I really wish the manual gave a temp compensation chart. I think what I'll do is head out there in the morning before work and check the resistance again. I'll post my results.


I suspect that when it acts up, you may find much higher resistance, even an open circuit, in one of them.

Anyone else in the group with YZ450?

I checked the resistance of coil 1 in the stator this morning. It was about 65 degree F. 1018 ohms puts it within range, but on the high side. I'm going to take the multimeter with me on the next ride this Saturday. If it acts up again, I'm going to start at the stator.

grayracer: Thank you for the help. I think you might be right. As the bike heats up things expand and I might get an open. I will let you know the results of the ride.


I decided to shop for a stator, and it appears my options are very limited. Either a $250 OEM or a $150 Electrosport that has awful reviews. Any other options out there?

Took the bike up to Bull Creek Ranch on the NV/CA border. Bike ran great at first, but about 30 minutes into the ride I noticed about a half second lag when I popped the throttle off idle. This is not typical of my bike. Killed it and attempted a restart, without success. Quickly pulled the seat and tank and ohmed out source coil 1. The little multimeter showed an OPEN condition, then after a minute or two it began to bounce between open and an outrageously high resistance. I took a brake and watched by buddy change main jets in his KTM 380 XC (test and tune day). I went back to my bike and found the resistance at 2000 ohms and dropping.

This is consistent with by original squawk. I suspect I never noticed the lag off idle due to the somewhat easy rides I've been on the last couple times.

Anyone know of a technical trails near Reno/Tahoe?


Bought a new stator from rocky mountain atv mc. Took about 30 minutes to swap it out, laid the bike on its side to avoid draining the oil.

Went out on a 4 hour ride today, performed flawlessly.

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