No compression problem! HELP!

11 replies to this topic
  • Polar_Bear

Posted May 27, 2002 - 09:08 PM


Ok. We go riding, I get my gear on and go to fire up my 01 426 and it wont start. Oh well, the worse thing is their is no compression. It was like kicking a two stroke! SERIOUS. Then my all knowledgeable buddy checks the plug, and their is no spark. Well we get it cleaned and sparking, put the tank back on and she fires right up. Get home and try to start it and same thing, no compression at all! Went riding today again and it was fine, power and all! Whats going on? Anybody know? Are my rings worn out or is the carb screwed up. Spark plug was kinda fowled too. Please Help! :)

  • Le_Racer

Posted May 27, 2002 - 09:39 PM



Haven't heard of anything like this but, if I had that problem, I would take a good look at the decompressor mechanism/cable.

Have you crashed the bike and damaged the decomp. lever or cable?
Is there anything stuck around the lever in front of the head?

Good luck!


  • MOmilkman

Posted May 27, 2002 - 12:37 PM


I had this exact same problem on my 99 WR.

You could kick it through with out even using the decompression lever. Once I got it fired up it ran fine. After that if you shut it off the compression was there again.
Then a few days later, no compression again.

That was over a year ago and I have never had a problem with it since. I was attribuiteing it to a exhaust valve sticking. (and I did check my compression release cable and it was not binding)

Weird deal but I never found a answer. The problem just went away.

  • thumperjp

Posted May 27, 2002 - 01:58 PM


I had same problem sometimes,too.
Then there is always no problem around decompression system.

After check,I tried to start engine.
When I kicked many times, it became back.
and I could start.
When it was cold or after long rest, it happened.
I think it's sticking valve system cause of less or tight oil.

  • yznvegas

Posted May 27, 2002 - 05:38 PM


It sounds like a malfunctioning decompression lever. Don't ride it like that because riding with that lever engaged is supposed to damage your engine. It doesn't sound like a serious problem because when the bike is running, it is running good.

  • BigLou

Posted May 28, 2002 - 02:48 AM


Seems like I've read about the occasional valve sticking open. Here's what to do: After you shut it down, always kick it through to the compression stroke so none of the valves/springs are left sitting in tension.

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

Posted May 28, 2002 - 03:48 AM


I had the same issue, I found it to be the routing of the decomp cable, seems the guy before me when he replaced the top tripple with a set of applied and protapers, he placed the decomp on the wrong side of the clutch

When the bars were turned to the left the decomp engaged slitly just enough to open it up.

Not sure if thats your case. Though there has been posts with the same problem, dont know the outcome there do a search though may come with something. :)

[ May 28, 2002: Message edited by: EgoAhole ]

  • Shawn_Mc

Posted May 28, 2002 - 12:44 PM


My bike has done the same thing after sitting for a while. It cant be the decompression sticking, because if it stuck youd never get the thing started. It would fire, belch and die. My bike hasnt done it since I quit using Mobile one. Ya, Im gonna get flamed, oh well. Try putting a little two stroke oil in the fuel, about 200-1. It should free up the valve thats sticking.

And if your carb is right, it wont foul a plug.

  • sirthumpalot

Posted May 28, 2002 - 02:44 PM


I had the same problem once and I know that it wasn't the decomp lever. I had it idling then stopped to clean the carb. First thing I always do is kick it around until it's on the comp stroke to close the valves. Well I hosed the inside of the carb good with carb cleaner (which went strait down into the motor) and when I tried to start after the first kick there was no compression at all. I kicked it 5 or 6 more times and it fired and ran great. I let it run for about 10 seconds and shut it off and the compression was back. That was several months ago and I haven't had the problem since. The carb cleaner must have clened the oil off of something (valve stem maybe?)???

  • Boit

Posted May 29, 2002 - 05:16 AM


Thumperjp, I think you might be onto something there with that "tight oil" theory. It might fall right in line with my theory about the cams being out of round. Mine have those oval shaped hunks of metal on the shafts. Probably causes eccentrically displaced piston reciprocation systems. I dunno.

  • sirthumpalot

Posted May 30, 2002 - 11:53 AM


I think that "tight oil" was a translation mistake. I'm guessing English isn't his first language.

  • Boit

Posted June 01, 2002 - 03:15 PM


I sorry. Couldn't resist the temptation.

Related Content


1998 yz400f will not idle. by trolley

Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • Hot  32 replies

Yamaha YZ450F 2017 by Chris.GVS

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

The "going back to the other darkside" adventure... by Monk

Dirt Bike   Make / Model Specific   KTM   250/350/450/505 SX-F & XC-F (4-Strokes)
  • Hot  113 replies


Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • Hot  30 replies

Chubby dad, looking at bikes , First trip to the orange/black forum ! by Slow_ride

Dirt Bike   Make / Model Specific   KTM   250-530 EXC/MXC/SXC/XC-W/XCR-W (4-Strokes)
  • Hot  28 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.