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syf350

04 YZ450...getting ready to be a boat anchor!

15 posts in this topic

This thing is driving me to drink, which is difficult to do considering how much I already drink.

I have an 04 I am trying to sell, but need to get running. The buyer took it to a friend of a friend of a friend mechanic with no luck.

No spark. New plug, have replaced the coil, the CDI and the stator. Wiring checks out and kill switch is good.

I am going to pick it up this afternoon to try to tinker with it myself, I reallly need to get it running.

Any ideas? soemthing we are overlooking? anything else that could prevent a spark?

TIA.

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soemthing we are overlooking? anything else that could prevent a spark?

Kill switch.

Also, test the wiring by using a VOM from one end to another of each lead.

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Thanks.

Kill switch is definitely good. They said they tried a new wiring harness as well. I'll go through the wiring a little more to see what i can find.

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Check your Neutral switch. It is the sky blue coming out of your Cdi leading to the Neutral switch. You can bypass this switch by grounding the sky blue wire.

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The neutral switch will not prevent the engine from getting spark. It's function is to create a ground on the lead that connects to it as a signal to the CDI that it needs to lower the rev limit from 11.5K to 7K, and alter the overall timing curve as well. Even if the wire is shorted or open, it will not prevent spark.

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The neutral switch will not prevent the engine from getting spark. It's function is to create a ground on the lead that connects to it as a signal to the CDI that it needs to lower the rev limit from 11.5K to 7K, and alter the overall timing curve as well. Even if the wire is shorted or open, it will not prevent spark.

Sorry to say this Greyracer but you re wrong.

In the manual under checking ignition system on page 6-3 it says to-

Spark gap test.

Check entire ignition system for connection (couplers, lead and ignition coil.

Check ignition coil (primary and secondary).

Check CDI magneto.

Check Neutral switch.

Replace CDI unit.

Looks like the OP has done everything other than check the Neutral switch.

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The manual says you should lap your titanium valves, too. :thumbsdn: :thumbsdn:

Look at the schematic for any YZ450F through '09, and you'll find that the only place that wire ever goes is to a ground, and it runs whether it's grounded or open (in neutral or not). What possible condition is there that could occur on that wire that would prevent ignition?

It won't hurt to check it, but the only way it could be involved in a problem like this is if several wires in the harness were damaged at a single point n the harness, so as to short to each other.

The second error here is that the wire should be grounded in a normal state. It should not. Actually reading the neutral switch test on 6-5 would have revealed that continuity from the N switch lead to ground while in any gear is a faulted state, and that a ground should be present only in neutral. And, typical of the manual, at no time does it say why. The reason has to do exactly with what I posted earlier, and nothing more. Notice two things: the manual also does not say that the neutral switch will cause a loss of spark, and that the bike is expected by its engineers, it would seem to run, both in gear or in neutral.

If you were troubleshooting a problem with the rev limiter or symptoms of bad ignition timing, the neutral switch circuit is definitely the place to start looking, but not for a loss of spark altogether.

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Something that often does get overlooked is the possibility of a missing/displaced/sheared off woodruff key under the flywheel. Check for this by verifying whether the timing mark TDC agrees with actual piston position using a screw driver or other probe down the spark plug hole.

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What you say makes complete sense (now, lol) Greyracer (Grayracer) :worthy:

I still think that if the manual says to test the Neutral switch, I would test it. At least that it is not touching other wires.

Not trying to argue, just trying to work out why it says to check the Neutral switch in the ignition circuit??? It does not seem right to me either as the Neutral switch is supposed to be for the rev limiter. How can it interfere with spark other than shorting to other wires??? Once again the manual fails to mention anything about this.

This is probably because the manual is useless, and about as hard to understand as internet communication (or almost). :goofy:

Edited by Barra8

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Not trying to argue, just trying to work out why it says to check the Neutral switch in the ignition circuit??? It does not seem right to me either as the Neutral switch is supposed to be for the rev limiter???

I told you why. Some people do have more difficulty understanding things than others, particularly when it's something that will undermine their position.

Try this on any YZ450F, '03-'09 (EFI bikes from '10 up have no neutral switch): Assuming the bike runs normally, disconnect the N switch and attach a lead to the N switch wire by back probing, and bring the lead out to somewhere that makes it simple to ground it at will. Now start the bike with the lead open; it will run. Start it with the lead grounded, it will run. Now take the bike out and try riding it with the lead grounded, and see what the performance is like.

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I told you why. Some people do have more difficulty understanding things than others, particularly when it's something that will undermine their position.

Try this on any YZ450F, '03-'09 (EFI bikes from '10 up have no neutral switch): Assuming the bike runs normally, disconnect the N switch and attach a lead to the N switch wire by back probing, and bring the lead out to somewhere that makes it simple to ground it at will. Now start the bike with the lead open; it will run. Start it with the lead grounded, it will run. Now take the bike out and try riding it with the lead grounded, and see what the performance is like.

Yeah apparently it will lower the rev limiter to 7000rpm lol, (don't ask how I know that haha). My TTR250 revs harder than that. :goofy:

I must say Greyracer, you know your stuff. I really enjoy reading your informative posts and have learnt HEAPS! from asking you questions. In return I just like to say thanks HEAPS! and sorry if I ask questions or have doubted your unbelievable mechanical ability. :worthy:

Keep up the good work! :thumbsup:

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This just happened with my sons KX85. The kill switch wire had rubbed through about two inches from the CDI and was making contact. The bike thought it was being started with the kill switch held in. You said they checked it with a new wiring harness, maybe double check that.

I am no mechanic but I was thinking flywheel also.

Did you do all the electrical checks in the book?

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Thanks all. Didnt mean to post and abondon the thread. we are still working on it as we can. will update once we do some mroe checking and testing.

:cheers:

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