My GS has had some issues over the past year and my buddy and I kept thinking it had to do with the carbs and tuning of the bike.  So after going through the carbs (multiple times) and spending hours on trying to get it Colortuned correctly we finally decided we were going to do a compression test.  I warmed it up and rode it around block, came back and did the compression test on both sides, each cylinder got 90PSI, we were shocked as the lowest the book says that's serviceable is 114PSI.  We then did a leakdown test which showed pretty positive results, there was a bit of a loss but not much.  We removed the valve cover thinking that it could be the valves, checked them and found them all to be in spec, we went to lunch and came back to a cold bike, we decided to run a wet compression test but before that we decided to run the compression test again (dry and cold engine) and got 105PSI on each cylinder, more than what is was when the bike was hot!  So we did the wet compression test and got 150PSI in one cylinder and I think about 120 or 125 in the other (I don't think we waited quite long enough for the oil to coat the rings).  Our next plan is to take the head off and take it in to have it pressure tested and have the cylinders measured and honed as we are going to put on hew rings.  Years ago I had my bike in for serivce and they milled the head a bit to raise the compression, does this sound like we are on the right track?  Any other suggestions?

You got it.Hone the cylinders,pop in new rings and check the head.You'll be terorizing the streets again.

 Did you open the throttle during all the tests you did?

Before you pull the engine apart- warm the bike up ( idle for 5 minutes or so)  and recheck it.

If you don't open the throttle while cranking the engine over the pressures will read low (the 90 PSI readings you got for instance..). 

Thanks for the replies, the carbs weren't attached at the time so I didn't worry about opening the throttle and the bike did warm up and then I took it around the block before the 1st compression test where the result was 90PSI

Ok... I've brain farted about the throttle before and got a 90 PSI ish reading on both sides before- just thought I'd mention it.

You already checked the valves for clearance... and a leak down test...could you hear where the loss was coming from during the leak down?

No problem....

We couldn't tell where the leak was, we put our hands over the intake (didn't take the exhaust off to check there), when we do the rings we are going to do all new gaskets as well just in case.

Give it some Seafoam before tearing the engine apart.  In the oil it will help to free stuck rings.  It's cheap, easy, and can't hurt it!

http://www.matthewsvolvosite.com/chat/phpBB2/viewtopic.php?t=14219&sid=d355b3f1546c0255cb63d6a04e273f29

http://www.seafoamsales.com/products.htm

Cool... well the rebuild should cure any low compression ( if it's there or not  ...kidding.. ) issues you have.