To all you master mechanics out there.

I just recently got my motor back from a shop where they put in a new valve seat. It took a while to work out a few bugs with the ignition and the carb, and now, lo and behold, it has no compression, and sucks in slightly on the exhaust pipe when you crank it. Could the auto decompression mechanism be stuck? I'm pretty frustrated, as I'm not good at figureing out what's wrong with things, but I can usually fix things when I know what's wrong. Any help would be appreciated. I did pop open the valve cover to look at the timing marks on the cam sprocket to make sure it was timed correctly mechanically. Could this have messed me up? Thanks in advance for any help.


There is an old saying about things going wrong, that is to look at the last thing that was done to it. I have seen newly installed valve seats come right back out. :)

I think where I would begin would be a carefull valve adjustment. Good luck and let us know when you figure it out.

I would go back in and chect the valves again. If the decompression lever is stuck you'll have a tight valve. If you ran the bike at all it might mean the valves are seating and tightened up. Depending on the bike no fuel can seem like you have no compression. On my bike a dry cylinder kicks over real easy until I choke it than the rings seal and I can hardly kick it.

Moredesert; I checked the compression with a gauge. It read 32 PSI, the book says I should have better than 180. Honesty, I don't know how hard it is to kick over, as it has electric start (it's a 650L). It was having some carb problems, but I got that ironed out, and it was blowing unburnt fuel out the exhaust after a long afternoon of trying to get it to start. It does have spark. I'm thinking of having the spring tension checked on my valve springs, and while I've got the top end apart, I'm going to check for a stuck ring. I had checked the valves before I pulled the motor, and they all had slack in the rockers, but I didn't measure it. What concerns me is that when you place your hand on the end of the muffler, not only does it push out against your hand, it sucks in also. Is this normal? As I'm not the greatest mech in the world, this has me frustrated, to say the least. Thanks for your input.


I honestly wish now that I had posted here before I took the top end apart. There was play in the rocker arms, though I didn't measure it. I have examined the valve seats, and they appear to still be in place. A friend of a friend is going to check the head for me to see if it is leaking past the new seat. I plan on seeing if one of the rings is stuck as well. As the bike has sat for three years, all sorts of gremlins keep popping up. First it was the ignition, then the complete fuel system from the petcock to the carb. Now the top end. All sorts of other little annoying thigs as well, like the neutral start and clutch switch not working. I really appreciate yours and Moredesert's imput. Thank you.


Hutch; If its been sitting for a long time you could have a stuck ring. One more thing that might be a problem. If the head was off them is the cam timing right. If the valve are out of sink that would explane a lot of things. If you need help on setting the valve timing I have a XR600 book I could scan a page or two for you. Let me know I've had my 600 apart many times.

Pull your spark plug - squirt a couple shots of oil in there - put the plug back in and listen to the motor as you turn it over. If the ring is the problem then you will feel more compression. If it is the valves compression will feel the same.

Thanks for the tip and the offer. I already have a book, two in fact. One by honda and the other by Clymer. Since I've stripped the bike completely apart for cleaning and specing, and the head is already off, I'll just pull the cylinder to see what shape the rings are in. Again, thanks.


I should have tried that, I suppose. Now I'll just take a peek. I'll post to let you know what I find. Thanks for yout time and thoughs on this matter.


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