Decomp lever blues

4 replies to this topic
  • kizzle426

Posted February 06, 2006 - 09:17 AM


So I was hosing my bike off after some serious singletracking yesterday, and I started my bike up to ride it over to the truck after I was done. I started it then got off to turn the water off. I walked over to my bike, grabbed it, then I slipped and started to drop the bike. I grabbed for the left part of the bars and smashed down on the demp lever (accidentally) and it killed the bike in the most nasty sounding way. What kind of damage can this do? Should I be worried about it? It started right up after and ran fine. Thanks in advance.

  • grayracer513

Posted February 06, 2006 - 10:07 AM


If you hit the decomp lever at high speed, there is the potential that the right exhaust tappet could get broken, which could end up being catastrophic. This one event will most likely not have hurt it, but you shouldn't use the decomp lever as a kill switch either. That doesn't mean you can't use it to bump start the bike, though. Much lower engine speeds are involved there.

The noise you heard was due to the increased valve clearance caused by lifting the right exhaust valve off its seat. The danger to the tappet at high rpm comes from the tilting force that the valve spring applies to the tappet when it encounters the decomp shaft on one edge as it closes.

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  • 642MX

Posted February 06, 2006 - 10:12 AM


Before I had an auto decompression cam I had a few incidents like you described kizzle, don't be worried I'm sure everything is fine.

  • kizzle426

Posted February 06, 2006 - 10:17 AM


Thanks. It was low rpm so I think it'll be okay. It didn't sound like it crapped a valve out or anything.

  • cowboyona426

Posted February 06, 2006 - 12:29 PM


Do yourself a favor- rip the lever off, buy an 03 YZ 450 cam, install it, and thank us later! If you are considering doing the cam mod, let me know because I have an extra decomp plug if you need one.

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