03 YZ450F Stalls hot no spark - Help!?


14 replies to this topic
  • bluthndr

Posted June 11, 2012 - 04:15 AM

#1

This is a clarified version of my earlier post. 03 YZ450F I bought about a month ago. Runs awesome until it gets a good hot soak (couple miles or 5-10 minutes depending on how hard I ride it), then, SUDDENLY, it has no throttle resonse, and putts along just barely running for about 30 seconds, dies, and will not restart until it cools off. Then it will start great and run great for about the same amount of time until (I assume) is gets hot soaked.

So far I have:
cleaned the carb
rejetted it down two sizes (pilot and main) - and plug now looks pretty good
checked the airbox and filter for obstruction
replaced the plug (new)
replaced the coil (used)
replaced the stator (used)
replaced the wiring harness (used)

Previous owner replaced:
CDI box with a new Procom unit (looks new and I was given the box).
full C4M exhaust and header

Now that I have some spares, I rode it at Silver Lake last weekend, and it does, in fact, not have spark when it dies hot. Nice bright blue spark cold (way better than my 426). When it dies it will come and go (a bit) if I keep the throttle cranked open while it is sputtering (putt - putt - putt - putt - riiiiiiiip - putt - putt - riiip - putt - putt - putt - putt - putt - die). What 15-20 minutes. Good as new again.

What am I missing here?

  • walent215

Posted June 11, 2012 - 04:18 AM

#2

same symptoms i had when my 03 coil was bad....i see you say that you replaced it but if it was a used one it may be the culprit ....

  • marv02

Posted June 11, 2012 - 04:24 AM

#3

Like I said new dont mean it good and it USED yes it could be just as bad as the one you are replacing.


See if the coil off the 426 will fit on the 450 just to see what happens.

I still think it's the CDI.

  • bluthndr

Posted June 11, 2012 - 04:41 AM

#4

Like I said new dont mean it good and it USED yes it could be just as bad as the one you are replacing.


See if the coil off the 426 will fit on the 450 just to see what happens.

I still think it's the CDI.


Can't disagree with you there Marv. My thinking behind using used parts, was that just "shotgunning" some parts at it would be pretty expensive new, and I thought even if it is still not "right" at least it would give me a direction to go. I thought at least if something was wrong it would be a different sort of wrong, not the exact same thing (which it is).

Pretty much where I'm at is try a new CDI box or TPS, but wanting to make sure I am thinking right before I drop another $150 on my "budget" weekend trail/dune machine. In all honesty, from my automotive background, a bad coil makes sense too.

I did look - although a lot of stuff is similar between the 426 and 450, pretty much none of the electrical stuff is interchangeable. 426 is seperate coil system while 450 is coil on plug...

Honestly, if I really knew a coil and CDI box would fix it for sure, I would buy both new and be done with it, but I still feel shaky. Maybe it is the only way though.

Edited by bluthndr, June 11, 2012 - 04:43 AM.


  • marv02

Posted June 11, 2012 - 04:55 AM

#5

My KTM did the same you YZ doing I did everything else trying to find what was the problem it end beening the CDI I lucked out and picked up a Use CDI off E-Bay I think it was $50.00.


I know buying used is a gamble but some of the sellers tell you if it dont work they will take it back either send you anouther one or refund you money.

  • walent215

Posted June 12, 2012 - 04:39 AM

#6

pick up a coil first...i sold a used cdi for next to nothing on ebay a while back...you may be able to find what you need there....



  • bluthndr

Posted June 12, 2012 - 07:51 AM

#7

Got to thinking about the coil. When it died I actually got a spare coil and plug out (ambient temp not hot like the one still remaining in the bike), and it produced no spark after the bike stalled. Two different coils, two different plugs, at two different temperatures had no spark when the bike was hot. I am hopeful on the CDI - my only reservation being that it is probably the most recently replaced (and newest) part on the bike (that the previous owner replaced) and I doubt he replaced it "just because." It does seem like at least a few on here and other forums have had problems with the Procom CDI unit, even with relatively new ones, so I will keep my fingers crossed that the magic black box will cure it all.

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  • MaxPower

Posted June 12, 2012 - 08:15 PM

#8

I may have a CDI for that bike. I have a coil and a stator. Pay for shipping, try them and send them back . Can't see it costing more than 7 to ship

  • MaxPower

Posted June 12, 2012 - 08:16 PM

#9

For the hell of it, pull the kill button. It doesn't cost anything to test.

  • bluthndr

Posted June 13, 2012 - 05:34 PM

#10

I may have a CDI for that bike. I have a coil and a stator. Pay for shipping, try them and send them back . Can't see it costing more than 7 to ship


Appreciate the offer. Already have a box coming that was supposedly tested good. I will let everyone know what the results are hopefully after this weekend. If that fails I'll take you up on that offer!

  • marv02

Posted June 19, 2012 - 06:19 PM

#11

Did you fix the bike and what was it if you did.

  • bluthndr

Posted July 05, 2012 - 12:28 PM

#12

Replaced "new" Procom Engineering CDI box with known good used (stock) CDI box, and rode the bike longer than I ever have, and in 90+ degree heat no less. Pretty confident it fixed my issue. Time will tell. Beware the Procom CDI boxes - I found other instances of problems with their boxes similar to mine. In all fairness, I sent them an email to see if they stand behind their product or if they would offer anything - a good replacment unit perhaps? If/when they respond will update the thread. In the meantime, hopefully this helps someone else out and saves some time.

  • marv02

Posted July 06, 2012 - 04:30 AM

#13

Great to hear you fixed it yes I had a bad CDI before like I said before it took me a while to figure it out also so dont feel alone LOL. :-)

Replaced "new" Procom Engineering CDI box with known good used (stock) CDI box, and rode the bike longer than I ever have, and in 90+ degree heat no less. Pretty confident it fixed my issue. Time will tell. Beware the Procom CDI boxes - I found other instances of problems with their boxes similar to mine. In all fairness, I sent them an email to see if they stand behind their product or if they would offer anything - a good replacment unit perhaps? If/when they respond will update the thread. In the meantime, hopefully this helps someone else out and saves some time.


Edited by marv02, July 06, 2012 - 04:31 AM.


  • bluthndr

Posted July 31, 2012 - 11:58 AM

#14

Almost a month now and no response from Pro Com. Interestingly enough, going through the spoils from my basket case purchase, I found ANOTHER Pro Com CDI unit in the box for the one that was causing my problem. It was new looking but dirty enough that it must have been on the bike at least once. Beware Pro Com CDI boxes!

  • mjb0152

Posted September 22, 2012 - 05:58 PM

#15

I am so glad I found this thread. I have beating my head again the garage wall for about 2 weeks now
trying to figure out what was going with my 2005, YZ450F. This is the same exact problem I have been
experiencing. Give me something to look into and not poking and hoping. Thanks for posting.





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