is the ignition coil on a yz250f compatible with a wr450f?

OK, so For a long time ive been trying to fix the issue of my 450 stalling when its hot, the throttle response goes to hell, and it likes stalling while idling and coming out of idle, when hot, always have to be on the gas to keep it running. When it is stone cold, I can slam the throttle wide open idle it until its hot, runs how it should while its warm.

I've checked valve clearances, and rebuilt the carb, only thing I can think of is the coil or CDI now, even took it to a mechanics and he couldn't fix the problem... just made it a bit better.

My friend has a 03yz250f - would I be able to take the coil off of his bike and try it on my wr450, just till it gets hot and see if it stalls out. If that doesn't fix it, would I be able to swap the CDI?

The coil might fit (I don't know ) but the CDI will definitely not work. The advance curves will be all wrong for the larger bore, and yopu run the risk of floating the valves if you grab a handful because the rev limiter on the 250F is about 3000 rpm higher than your 450.

Does not sound electrical, sounds like you are way rich on the pilot jet/fuel screw.

won't hurt the coil though?

William- Ive tried 2 different pilot jets (45 and 48) and all of the screw settings +/- on eighth turns out from top. All the mechanic did before was get it a little more exact than I did, its not a carb issue lol

When a coil or stator fail, it is when hot. First getting worse at high rpm. Starts as a high speed slight miss and over time it will get to where a bike will not rev at all. The second any load is placed on it it, it stalls. You are saying that once you get it off of idle, it runs 'ok' when hot. That is not indicitive of a failing coil or stator. CDI failures manifest the same, hot or cold and again, get worse with more rpm. Usually, they simply just fail completely.

The fuel screw/pilot setup is definitive regarding pilot jet selection. It is not a subjective sort of thing. It is very definitive.

The coil swap is a ok test but it is the wrong way to diagnose a problem. Swapping parts without proper tests will have you chasing your tail. You cannot swap CDEIs though. Your CDI is DC, the YZ is AC.

Very few if any bikes will accept WOT from idle without stalling. No one rides a bike at idle then goes WOT, it cannot be done anyway. If your bike is fine when rolling on the throttle and merely has a nasty bog at low RPM then your focus should be on the AP.

"The second any load is placed on it it, it stalls"

Itll do that when its very hot, after being ridden hard for a while, it wont like running smoothly, stall and not want to start, but if i let it cool it will be ok, but a pain to keep running, I figured I was over heating it. (though now that I think of it my friends yz250f would still run fine... when my wr started to do this)

I seem to have the AP pump dialled in (but can't tell for sure due to above) I can blip the throttle and it makes a crisp brap, Also did the O-ring mod.

Edited by ecookman

Sounds like mine when it was coil. Try swaping it and if it does not stall thats it..It was on mine did swap with a yz450 good luck!! I'm taking bets on the coil!! Try your coil on his..

Edited by mtahoe

I have a stock coil to fit your bike and I have a extra Black Ops Moto coil sitting here too. PM me if you need it.

I may, friend with the 250 is comin over in a few hours

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