Loss of compression?

7 replies to this topic
  • kroolio

Posted February 09, 2004 - 08:00 AM



Just wondering if anyone has any ideas. Basically my bike has lost a lot of compression for no reason. I rode my bike and put it away in my garage two days later went out to start it and nothing it seemed like it was flooded so i drained the carb and tried starting it and it sounded like it was bogging so i tried bump starting it. nothing. next day went back out to it and it had lost a lot of its compression. i have tried turning the petrol of kicking through 40 times and no compression regained also tried with the decomp lever in.nothing.

the decomp appears to be moving smoothly as i took the bolt out of the side of the cylinder and can see a small cylindrical connector turning.

i have a spark, petrol is going through and air appears to be ok. any ideas at all anyone. id really appreciate if you could help.

I cant understand this as before i put it away it had loads of compression and was riding really well.

Cheers everyone.

  • kph

Posted February 09, 2004 - 04:26 PM


I hope somebody replies soon as I am having the same problem. It seems to have started after my throttle stuck and I attempted to start it numerous times. I would get good compression off and on until it no longer built at TDC. 01 WR426

  • Bagwell

Posted February 10, 2004 - 06:33 AM


im not sure whats happening exactly, but if you get enough fuel into the cylinder you wash the oil off the cyl walls and it doesnt build compression as well. there is not gas in your oil is there? Just a couple of thoughts.
Good luck and let everyone know what you find,

  • 5spoke

Posted February 10, 2004 - 07:29 AM


I would change your oil and see what you find in it.

I think guys will help you here, but you have to give them more info. I would list your bikes details so everyone will know exactly which bike and whats on it. Then you have to at least do some small things like change the oil, check plug etc, and give feedback.

Welcome! :)

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  • Frostbite

Posted February 10, 2004 - 07:56 AM


The same thing has happened to me probably for different reasons than you boys but the same fix should apply. The first time I lost compression I checked all the obvious and then thought flooding had washed the cylinder down. What I found was that condensation had formed and frozen on my valves and was holding them open a bit(they had been open). I heard of some southern WR's with the same condensation forming (usually after long storage period and causing enough corrosion so the valves can't seat properly. I guess that the springs are so light they can't overcome the crud. My fix is to get into some heated space and the frost melts. Maybe if you boys put a shot of oil in the cylinder and kick for a while they'll loosen up. To prevent this from happening, I always set my bike to TDC after I shut it down. That way the valves are closed and no matter how much ice forms on the stems, the cams are going to force them open and scrape it off. The engine probably ends up at TDC most of the time when you shut down simply because that's where the piston meets resistance and stops so you rarely see the problem, but if you pop the clutch to stall it after you ran it up in the back of your truck, it could sit with either set of valves open.

  • kroolio

Posted February 10, 2004 - 12:11 PM


thanks for the replies so far. it is a completely stadard 2001 WR 426 i have checked the plugs and ive got a strong spark. i will look into some of these other options as well thanks for the feed back so far. i was just wondering if it would have been possible for the valve to get stuck open when i tried bump starting it.

Thanks again.

  • Frostbite

Posted February 10, 2004 - 12:44 PM


I can't see how bump starting would make it any worse unless a valve was stuck waaayy open and kissed the piston. Did you try putting a shot of oil in the cylinder while you had the sparkplug removed? If your cylinder has been washed from flooding, the oil will bring the compression back instantly. I'd put my money on a sticky valve though. If you pop off your headpipe you can spray a little WD 40 into the exhaust port to coat the valve stems. Spray a little, kick a little, spray a little......You can also pop off your carb or just remove the air box boot and hold the throttle WFO and spray at the intake valves through the carb. It took me about 15 minutes of kicking to get mine loosened up the first time, spark plug out, no decomp lever. If you hold the decomp lever in you're defeating the purpose of trying to get the valves to sit in their seats. Hope this works for ya.

  • kroolio

Posted February 11, 2004 - 07:34 AM


thanks guys all of this is a great help. i will try this as soon as i get the chance to. if any one else has any ideas that would be GREAT. any way thanks for the help so far.
cant wait to go for a ride now....


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