loss of power - compression problem?

6 replies to this topic
  • yzf_rider400

Posted August 27, 2004 - 09:12 PM


was riding today and after a couple of hours I suddenly lost a noticeable amount of power and the bike would sort of sputter (the power would come on and off in quick succession). I looked at my header pipe once I got back to the truck and noticed the retaining socket cap bolt had fallen out.

Do you think this would decrease the seal enough to lose compression and create the problem I'm describing. I should mention that I wasn't using a header gasket (dumb ass) -- but I've never had the problem before.

Other possibilities I could think of would be the decompression lever (the one mounted to the engine) got stuck open somehow? Or maybe I've got a dirty carb (although my dad and I cleaned it not too long ago).

Your thoughts and suggestions are appreciated! :thumbsup:

  • Hamish

Posted August 28, 2004 - 02:20 AM


unlikely that the loose bolt would cause a noticable drop in power. Would make it backfire on deceleration though.
If the decomp system was activated the engine would instantly stall. I'd start at the carb, then do a leakdown test and check the ignition system.

  • Chris_from_Oz

Posted August 28, 2004 - 02:28 AM


I would start by checking your air filter, then move on to the carb' etc as Hamish said. :thumbsup:

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • yzf_rider400

Posted August 28, 2004 - 08:31 AM


thanks guys, I'm going to check it out today. You think I might have a fouled plug? I'll check the air filter, but I did just clean it two rides ago.

  • Butta

Posted August 28, 2004 - 10:55 AM


Well, that's not really important how many rides it's been since it's been cleaned. I have clogged my air filter with one 10 minute ride in Glamis, then other days have ridden all weekend in Colorado with no problems... :thumbsup:

  • yzf_rider400

Posted August 28, 2004 - 02:43 PM


butta... You may be right. I'm going to clean it again before I go ride, although it doesn't look very dirty. I pulled the fuel tank and checked my spark plug (looks fine) I think I may not have had my spark plug cap fully seated though (would this cause the problem). I reinstalled everything and she starts up and sounds good now. hmmm... hopefully she'll keep her [@#$%&*!] together now. :thumbsup:

  • Butta

Posted August 28, 2004 - 09:07 PM


Hopefully that was it! Most of the times I've been concerned about a lack of performance or hear a different sound the solution is an easy and quick fix (generally caused by something I did - or didn't do). These bikes are great! Incredibly reliable for what we put them through.

Related Content


Yamaha YZ450F 2017 by Chris.GVS

Yamaha YZ450F 2017
  • * * * * *
  • 1 review
  • Last review by Tommyk_55
  • On January 15, 2017

05 yz450f not fast enough by RedeyeYZ

Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • Hot  38 replies

Wilson the Blue Privateer by jetfuel

Dirt Bike   Special Interest Forums   Pro Racing
  • Hot  50 replies

2016 YZ450 by CaptainKnobby

Dirt Bike   Dirt Bike Technical Forums   Suspension
  • Hot  59 replies

BIGBORE FOR YZ450F 2006? by Taattie94

Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • 5 replies

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.