Lost compression

5 replies to this topic
  • hotdog7

Posted October 05, 2007 - 05:03 PM


Today went for a ride on my 426 stoped by a friends house turned off my bike waited for him to get ready then when I went to start my bike it seemed like it lost compression not all just some as I was able to push the kick starter down with my hand not very easy but I cant even move it with my foot without the decompresion at top dead center any other time so anyway it would not start so I made sure the decmpresion was not par shall engauged and it was not so I got a ride home picked up my truck and before I loaded it I tryed it again and it was back to normal went for a ride for an hour had no more problem what could have gone wrong? was a :confused: valve stuck open?

  • brt 426

Posted October 06, 2007 - 03:09 AM


When the engine was turning over easily , could you hear where the air(compression) was going. ie out the exhaust or out the aircleaner. What was the last thing you did to the bike before you rode it. Did you clean the airfilter or maybe washed it and left it for a couple of days. I have heard of debris getting in through the aircleaner and holding valves open. And also corrosion forming on the exhaust valves causing them to stick also. But I think you will need to check your decomp cable carefully. As it was the last thing you did before kicking it over to start it.

  • hotdog7

Posted October 06, 2007 - 04:27 AM


The decompres was ok I did not check where the air was going because I was going to bring it home to check everything but when I got back it was ok again. Now I am afraid to go for a long ride and break down.

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  • WR_Dave

Posted October 06, 2007 - 07:49 AM


I would go through a valve setting and see where everything is set. How many miles on the bike and how good is your service schedule. It may be time to recondition the cylinder head. Sounds like a sticking valve. That's why I tell everyone to always set the engine to TDC when you shut the bike down, that way the valves are all in the closed , relaxed position. My .02 -- WR Dave.

  • hotdog7

Posted October 06, 2007 - 06:09 PM


I have no idea how many mile is on bike I was hopeing to get to the winter before checking valves as I bought the bike used two months ago I do keep up with things change oil every 3 to 5 rides with amsoil and air filter cleaned every 2 or 3 depending on dust most of the time I ride first so not much dust.most rideing is 60 to 80 miles.I wil make sure tdc next time thanks WR DAVE

  • Alternative

Posted October 06, 2007 - 06:31 PM


I have experienced this on my 426 several times. After the first time I researched the problem and found that what happens is raw fuel gets in the cylinder and washes all the oil off the rings, meaning they don't seal properly and hence the engine looses compression. I know it sounds weird but lots of people on here have experienced it, it's just another quirk with these bikes.
To fix it, I find giving the bike a couple good kicks works, the compression will start to return and then the bike starts. Others pull the plug and pour a teaspoon or so of oil into the cylinder which seams to work also.


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