Decomp not dissengageing?

4 replies to this topic
  • Wondermutt

Posted September 28, 2011 - 05:56 PM


Hey all, I own an 02 yz426, had it since new, and recently brought it out of the mothballs from about 3 years ago. I went through it, with the basic maintenance to get her up and going again, oil, filter air and oil, new fuel. I took it out, and the piolt jet was plugged up, ran it like that for about 20 mins or so, up on the main curcuit, seeing if I could get her unclogged, but to no avail. Turned the carb when I got home, and dropped the bowl, cleaned up all the jets and cleared the pilot out. Now I went to start her up, and I can cycle through with the kick starter without needing to pull the decomp lever. The bike is all stock except for jetting and exhaust. The kicker does give some resistance, but nothing like it used to. It used to just stop dead on the compression stroke, now I can move through it with some resistance, when the decomp is pulled it is easier, but it will still go through both strokes without it being pulled. should I be looking at the decomp as the culprit, or something worse, such as the valves or top end itself? Ive never had it torn down, it was always a great runner,always started on te first or second kick, even this last time after sitting for a few years, never hammered on just basic trail ridden with the occasional blast down a sand wash from time to time, but I dont bounce off the rev limiter and mostly am down in lugging mode. Any suggestions would be greatly appreciated


  • hoss400

Posted September 29, 2011 - 08:34 PM


Check to see if cable is frozen? does the decompression cam move?

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

Posted September 30, 2011 - 03:04 AM


Yes, I have taken it all apart. It will start now, but I can still kick it through without having to use the lever, there is more resistance then before, but I am still getting bleed by, which wasnt the case before I cleaned the carb out. My only thoughts are that it must be time to adjust the valves, and put a new piston and rings in her.

  • grayracer513

Posted September 30, 2011 - 07:13 AM


When you check the valve clearance, be immediately suspicious of any that you find that have more than the specified clearance. Normal wear reduces clearance. If you find one that has more than it should, that valve may be sticking open due to carbon on the valve head or stem.

See if it will "bounce shut" by tapping prudently on the lifter with a punch with the cam lobe pointed up away from it. Give it a tap or 3 and recheck the clearance. If it closes back to a normal range, run some injector cleaner through the next couple of tanks.

  • Wondermutt

Posted September 30, 2011 - 05:40 PM


Thanks for the info, I had never thought of that, will do

Related Content


First Hare scramble tips by dhend8

Dirt Bike   General Dirt Bike Forums   General Dirt Bike Discussion
  • Hot  33 replies

Michigan Motocross Tires by 288yz450

Dirt Bike   Dirt Bike Regional Discussion   North
  • 1 reply

Megabomb Fitment by 288yz450

Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • 1 reply

James Stewart back on a YZ450F by YamaLink

Dirt Bike   Special Interest Forums   Pro Racing
  • Hot  47 replies

Snake pit oct 30th by The Anvil

Dirt Bike   Dirt Bike Regional Discussion   California
  • Hot  293 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.