No Engine Compression

Bike ran fine when put up. Went to start it today and kicks over like the decomp is held partially in. Decomp is not sticking at the lever or on the engine. Any ideas on sudden loss of comp??

Yes, several of us on 426s and 250s have had a temporary loss of compresssion. I pulled my head right after it happened last time and was convinced that a large hard buildup on the exhaust valves was the culprit. It wasn't, when I had cleaned it and put it back together, it still didn't have compression. But like the first time, when it started once, it was fine again. No one knows why.

Just kick or roll it until it starts. Then it will be fine. There are several posts. Try 'lost compression' here, on the YZ426 and the 250F forums.

Good luck,


I think a burr can be created on the valve cap from using the decomp excessively or if it get touched/bumped while running. This I think when bad ends up rubbing/catching and keeping the valve open. The roll starting may remove the burr or something if the theory is correct ?????????. Worth a look. Hope this helps.


I had the same problem on my 01WR426 , after leaving the bike sitting for several months whilst my busted arm healed.

The valves get sticky and don't seat properly. I pulled the rocka cover off pressede o nthe valves everthing. Had to kick the absolute crap out of myself tyo get it going. As soon as it fired the valve came free.

Leave the bike at Top Dead Centre whenever you store it and you should be ok. :)

Hey Jekel,

As Mark said, there has been recent discussion on this exact topic over on the YZ side.

Sounds like this problem is more common than I thought.

Just kick it untill your blue, then kick some more. Once it fires up and runs for a bit the problem seems to be gone.

Boy, and I was getting scared. Mine did the same thing last week. I had pulled the hot start instead of the choke. And was kicking when I noticed I was kicking straight through like it was a 90 or something, no longer stopping at TDC. I walked away cursing, came back in 5 minutes, gave it one good kick (with Choke this time) an it ran fine.

In response I checked the valves which is a good thing because the dealership must have forgot as I had 4 tight valves.

Anyway, its good to know that my top end is okay. I'm still a little concerned about the kickstarter though as sometimes it seems to slip, like the ratchet is missig a gear or something.

I thought kickers tendedto break at the lever not in the engine.

Any comments?

I got it started. took about 10 minutes of kicking. Then it would start and die when I even thought of touching the gas. This for about another 10 minutes. Now it is doing fine. I do leave it at top dead center when I park it because of reported problems. Don't know what the deal was??? I think she was just jealous I was working on other bikes all weekend. I think i will look at the valves this week though. :)

Mine does it all the time. I usually just kick the thing and usually the next time I check I've got compression back.

DL :)

In most of the cases described above, the symptons are the result of sticking valves.. by the time you have five of them the probability increases. I have found an easy solution to be:

- Squirt a small amount of engine oil into the combustion chamber via the spark plug hole

-Roll down a hill to bump-start

or kick it lots (as described).


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