Bad Using Decom lever while bikes running

11 replies to this topic
  • XR250_RIDER_14

Posted September 24, 2006 - 04:30 PM


I have an 03 450. Is it bad to hold it in while the bike is running for downhill and stuff since it is less compression braking but not to much? I have been doing it alot lately and was wondering if it could be bad for it. Doesnt the lever just hold open an exhaust valve like the XR's do? how does it work?

  • XR250_RIDER_14

Posted September 24, 2006 - 04:31 PM


Definitely makes it backfire alot by the way. my 450 always backfires on deceleration anyway while in gear.

  • 642MX

Posted September 24, 2006 - 04:39 PM


450's don't have a decompression lever. :thumbsup:

  • SureBlue

Posted September 24, 2006 - 04:41 PM


No wonder it backfires because it's the hotstart, you don't have a decomp lever on 450, it has autodecomp.

  • kyleyz

Posted September 24, 2006 - 04:45 PM


lol noob! HAHA

  • TapptOut

Posted September 24, 2006 - 04:57 PM


Good Eye :thumbsup:

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  • seizedcrank

Posted September 24, 2006 - 05:25 PM



  • grayracer513

Posted September 24, 2006 - 07:57 PM


For the record, if you actually did have a compression release, it would be very unhealthy to use it with the engine running. The exhaust valve lifter was never intended to bash into the compression release shaft at engine speed.

  • ben_suhard

Posted September 25, 2006 - 10:14 AM


Is it bad to hold it in while the bike is running? I have been doing it alot lately.

You're lucky it wasn't a decomp lever, you can bend a valve doing that!

  • grayracer513

Posted September 25, 2006 - 10:23 AM


It's unlikely that a valve would bend, since the system is designed to allow the engine to turn completely through and over top center with the compression release pulled. The biggest problem is that the cam is not ground to set the valve gently against the CR shaft, and that means that at speed, the impact of the cam follower hitting the shaft as the valve closes is fairly high. Additionally, the impact is well off center on the lifter, so the impact causes a rocking influence at the tappet, which can cause the tappet (cam follower, bucket, valve lifter) to break, which, of course, is ugly.

  • ben_suhard

Posted September 25, 2006 - 10:28 AM


It's unlikely that a valve would bend.

That's just something I read in MXA mag, they said that's what can happen, dunno. :thumbsup:

  • TexN343

Posted September 25, 2006 - 10:51 AM


The hotstart lever would cause it to be very lean. You say you pop during deccelleration? That's a sign of a lean bike. Try adjusting the fuel screw and if that doesn't work your gonna have to rejet.

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