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brettmac

09 YZ450 Kicking Over Easy

13 posts in this topic

Eh bi's. Got my 09 yz450 around the start of june. Drove it almost everyday this summer. Great bike, wheelies like a dream and no major problems just tires and bearings.

I have noticed lately that its been kicking over rather easy and im wondering if this is a sign that im losing compression in my motor. It does usually start 1st kick in the morning but i know theres a lot of people on here that know more about serious engine things than me.

Just wanted to hear what you guys have to say about this issue. Thanks.

Stay golden.

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If its starting and running well I'm not sure there's a problem. Have you checked your valve clearance ever? (I know its a YZ shouldn't need it)

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What I've heard (hopefully you get Gray to respond) is that sometimes 'loose' valves (remain partially open) would cause this lack of compression...

My YZF 450 valves are actually (for some reason) 'loose' and I'm trying the 'run' a few tanks thru with Fuel Injector cleaner' and remeasure technique right now. Theory is dirty valve slightly sticks open...

Not sure thats your issue, but I'm investigating it as my issue...

See this link (might be worth a sticky add sometime if this is common)

http://www.thumpertalk.com/forum/showthread.php?t=1011678

Edited by NewMexican
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Not sure what experience you have as a rider,but if you know someone with the same bike try comparing kicking their bike over with yours,could just be that your leg is getting stronger...(sounds odd but it happens).

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When you say 'loose valves' do you mean valve lash?

You could have somehow over revved it and floated valves so your loosing compression.. Even tho our bikes have rev limiter's you still can over rev them by down shifting at to high of an rpm or missing a shift.

I know alot of people might think its a bad idea but I did it to a old 110cc pitbike. It ran great after that and a valve never broke.

On a expensive bike like a 450 I would recommend replacing the valves but dave shows how to tell if there bent.

http://www.youtube.com/watch?v=92VxU_652bM

http://www.youtube.com/watch?v=92VxU_652bM

Davids farm rocks

Edited by Thepowderblue

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I have an '09 YZ450F with 91 hrs. Every once in a while, I'll find the bike real easy to kick over. I either put it in gear and rock back and forth, or just cycle the kickstart through a few times, which finally puts the motor in a condition of full compression. Then one kick...starts every time. This has been happening for perhaps the last 30 hrs.

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I know alot of people might think its a bad idea but I did it to a old 110cc pitbike. It ran great after that and a valve never broke.

I guaranty you that's a bad idea. It may actually work with lawn mowers and old pit bikes, but you'd be exceptionally stupid to attempt any such thing on an 11,000 rpm engine with titanium valves.

Everything about the first video is wrong as applied here, including the "information" regarding cam timing.

Dumbest thing I've seen in years. :smashpc:

As for the "publisher"...

INetStup125503503032.jpg

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Really they rev to 11k?

My yz450f seems to hit the rev limiter way sooner

If it where on my 450 I would just replace it.

If he was wrong on the cam timing how come that quad fired up and ran perfect?

He he said the stem is hard and brittle but there is a soft spot on the valve so It can flex and thats where it bends and where you unbend it.

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Another thought could your decompression be stuck adjusted wrong to the point where its cracked open

There is, in the first place, no adjustment available or needed on the YZF auto decompression mechanism. It is also extremely unlikely that it is stuck, but even if it were, it could not reduce cranking compression below normal levels. It would either be stuck extended, causing normal cranking compression and extraordinarily noisy valve train while running (probably breaking the lifter in short order), or stuck retracted, which would make it nearly impossible to kick over, but run normally.

Cam timing would be the only resettable feature that would have an effect on compression. Read the link posted earlier in post #3 by New Mexican. The likely cause is there.

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Really they rev to 11k?

My yz450f seems to hit the rev limiter way sooner

Be sure that the light blue wire running up from the neutral switch is not shorted anywhere. The rev limit on a YZ450F is 11,500 RPM.

There's all kinds of bullshit you can get away with on lawnmowers and farm implements that you should never attempt on a high performance engine.

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