cold engine compression

Just put oil and coolant in it and was kicking it through with the release in and then let it out to find TDC and it wasn't holding pressure like it used to. It hit the hard spot and then leaked through the stroke. Also it was around 15 deg F that day. It hasn't run since Aug 00 when I drained all liquids due to a broken ankle. I did adjust the valves during the time off that I don't think I had any problems there. So I was wondering if somone else had noticed reduced compression during cold weather. I will buy some gas this week and lite her up. I'm sure once the engine is warm it will be back to normal but just wanted to throw this out for options.



99YZ400F (him)

00TTR125 (her)

i was havving the same problem only it wasnt that cold. Even though the bike fires up fine it still will leek through the hard spots?????

Shawn: Did you change shims on any of your valves? If so, what change did you make?

You might try kicking it thru with the release held open for several kicks. What I'm thinking is that since the bike sat up for a while, there might be a valve stem hanging in a guide a little. Kicking it thru might free it as a little oil gets on the stem and lubes the guide. What you described happend to my KLX 250 once. It seemed to suddenly have little compression. I kicked it thru several times and then started was fine afterwards.

If you continue having little resistance at TDC, I'd suspect a too tight of a valve lash first. All it takes it for ONE valve to be too tight.

My 00-426 has done this a couple times,(22 degrees first time) the first time it really spooked me. Once the bike fires I haven't had any problems,or performance drop ? pretty weired though.


Just a thought: Did you have to adjust your valves? If so, you may want to double check compression release. If set screw is not in groove of shaft the release could stick. Also, the spring on shaft lever can rotate easily when shaft is out and may not be in place correctly. Both of these could potentially be holding one exhaust valve open. Check for freeplay in CR.

especially if you've done all this with the bike on left lock. that decomp lever is a sod!!!


I went and bought some gas and it started up after a few knicks and after it warmed up, it (compression) felt like it use to. I think it was just really cold. I did adjust the valves over the time off, but it was really straight up and easy to folow. Only problem is going to have to work on the new throttle cables free play as it was hanging up. Not as easy as the old 2-stroke!

Thanks for the comments


99YZ400F (him)

00TTR125 (her)

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