Is it possible to bump start a yz400f


8 replies to this topic
  • goldy1980

Posted February 18, 2009 - 06:32 AM

#1

I've got a YZ400F that simply won't start. Is it possible to bump start these bikes?

  • ace402

Posted February 18, 2009 - 06:48 AM

#2

Yes, get it rolling, put it into 1st or 2nd, and dump the clutch.

  • jrny426

Posted February 18, 2009 - 06:57 AM

#3

I used bump start my 426 on a little down hill out side my house and It would start locking up (Skidding) in lower gears so I feathered thd decomp lever to get the engine turning.Some people say you can damage the exhaust valve that way but I had no problems,

  • grayracer513

Posted February 18, 2009 - 07:07 AM

#4

I used bump start my 426 on a little down hill out side my house and It would start locking up (Skidding) in lower gears so I feathered thd decomp lever to get the engine turning.Some people say you can damage the exhaust valve that way but I had no problems,


There is no need to worry about using the compression release for bump starting, as the engine speeds are low enough that no damage will be done.

Pull the compression release and hold it while you run the bike up. Engage second, still holding the release, and get the engine turning. Ease the release out slowly, and be ready to grab the clutch the instant it fires.

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  • travisn

Posted February 19, 2009 - 06:46 AM

#5

Wow I was just thinking of this with the high compression. Good to know...

  • buzzfin

Posted February 19, 2009 - 02:19 PM

#6

If you have replaced your cam with the auto-decomp cam from the 450, it's super easy to bump start. My 400 will bump start when I'm barely even moving.

  • Emiliano

Posted February 20, 2009 - 09:36 AM

#7

There is no need to worry about using the compression release for bump starting, as the engine speeds are low enough that no damage will be done.

Pull the compression release and hold it while you run the bike up. Engage second, still holding the release, and get the engine turning. Ease the release out slowly, and be ready to grab the clutch the instant it fires.



some years back my friends YZ400 was warming up and some guy presed the comp relese lever and the piston knock the exaust valve and bended, I think the timing chain was 1 tooth off

  • grayracer513

Posted February 20, 2009 - 09:58 AM

#8

some years back my friends YZ400 was warming up and some guy presed the comp relese lever and the piston knock the exaust valve and bended, I think the timing chain was 1 tooth off

In the first place, that happened while the engine was running, and even at an idle, the internal speeds are much higher than when bump starting.

Secondly, if the valve would have hit the piston at idle, it would have hit it while cranking.

  • 400f mech

Posted February 20, 2009 - 08:01 PM

#9

i used to bump mine all the time down my hill, and never had the problem of the piston slapping the piston even if i accidently grabbed the decomp while idoling. and the auto decomp is definatly the way to go, i love it





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