Auto Decompression System-1990 XR600R

6 replies to this topic
  • BRP-rider

Posted September 11, 2005 - 05:42 PM



My Auto decompression system is giving me problems
with my bike when I kick it over. It's messing up my valve
timing. I talked to somebody about this problem and they said often the best thing to do to fix the problem is just to disconnect the Auto decompression system and remove it. If this is true, does any one have any idea how to do it?
:banghead: Thanks

  • bork

Posted September 12, 2005 - 10:39 AM


I took out my cam and removed . Back on the old forum, someone posted pictures and tools etc.. Made it easier . I like much better now . Starts better . Just slowly kick kick starter till it gets real hard , then hold your foot there with no pressure and squeeze the manual decomp lever(on handle bar) and slowly push down on your foot/kick starter about 2". Stop. Release decomp lever at handle bar and do a quick kick . Usually fires right up . BTW if I had to do over , I would not have screwed around with old cam (welding and pressing apart etc...) Just buy a after market and I think there is no decomp on it . Just reinstall !

  • miguelitro

Posted September 12, 2005 - 12:44 PM


Right- go with an aftermarket cam, no more auto decomp.
some say it makes the bike harder to start but i cant figure out how.
As a matter of fact i use the decomp lever just as bork says even with the auto decomp. My piggie ussually starts 1st kick as well using that method.
my .02

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  • BRP-rider

Posted September 12, 2005 - 03:10 PM


Wouldn't I just be able to reomove the Auto Decompression system from the stock Camshaft. :banghead:

  • miguelitro

Posted September 12, 2005 - 03:21 PM


yes but while you have it apart it is worth the extra $$$ to put in a hotter cam.
it makes that much of a difference.

  • qadsan

Posted September 12, 2005 - 03:36 PM


Wouldn't I just be able to reomove the Auto Decompression system from the stock Camshaft. :banghead:

Yes, you can remove it from the stock camshaft.

You remove everything between the cam lobe & sprocket flange / collar. I believe the xr600 uses a round cam sprocket where as the 650r has tabs / ears on the sprocket flange and you've got to be more carefull when pulling it off a 650r so that you don't break off the cam sprocket ears. There will also be a hole in the cam underneath the auto decomp mechanism for oiling the auto decomp mechanism and you'll need to close it with either JB Weld, epoxy or simply tack weld it closed (best choice). If you leave the hole open, then the oil meant for the decomp auto mechanism will run down into the cam chain cavity and into the sump when it could have been more effectively used for the valve train. There's also a plunger and spring in the cylinder head that works with the auto-decomp mechanism and you'll need to remove that as well which is fairly easy to do.

  • Thumpmeister

Posted September 12, 2005 - 08:13 PM


The simplest (and cheapest) way to remove the auto decomp system is to disconnect the cable that runs from the kickstarter to the top of the head. Just make sure you remove the correct cable.

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