How to compression test with auto decom and LOTS of smoke?

3 replies to this topic
  • Dave Blackburn

Posted February 17, 2008 - 08:13 PM


I have a 97 650L with electric start and auto decompression. How do you compression test with the auto decompression? Is there a PSI I should have with the decom working?
I just got the bike and still don't have a shop manual, so no help there.

Today when I started it there was LOTS of white smoke for about 4 or 5 minutes. It smoked me out of my garage!!!
What's up with that?
It was cold, but I just replaced the rings, piston, and all seals,m total top end rebuild. Everything else on the bike was good.
I rode it yesterday 100+ miles with no smoke at all???
If it is overfilled with oil woll that cause this? I only hav 2.6L in there. I think it was way too much smoke for some bad seals, which are new anyway.
Doesn't smoke when warm??

  • durandal

Posted February 18, 2008 - 08:31 AM



I just got the bike and still don't have a shop manual, so no help there.

If it's an R, the manual is available online for free in several locations.

If it's an L, PM me with your email. I'll send you the PDF.



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  • martinfan30

Posted February 18, 2008 - 11:18 AM


2.7 litres? I thinkl thats too much. Mine only holds 2.07 qts.

  • cleonard

Posted February 18, 2008 - 11:54 AM


+1 on too much oil.

New rings don't seal very well. A lot of smoke before it gets broken in can be normal. With 100 miles it should be mostly broken in.

There is a number for compression with the decomp, but I don't have it handy. I don't feel that it is a very good measure though. You can back off the right side exhaust valve adjuster several turns. This will have the effect of not letting the auto decomp be able to press down the valve. Then you can get a real compression reading. When you are done, readjust the valve to normal specs.

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