I just bought my first bike, a '99 yz400f, two weeks ago. I rode it three or four times and it seemed to run great except for a lot of backfiring on deceleration. Now after sitting overnight i can't get it to even try to start. I usually had some trouble starting it but figured that was do to my lack of experience. Now it seems to have low compression. It's not zero compression but i can now kick it all the way down with out using the decompression lever most of the time. All i can get out of it is an occassional loud backfire after many kicks. I use the starting drill outlined on this site. I checked the plug and it isn't wet and i don't think it's fouled but i'm not sure if i would know. The bike didn't seem to smoke at all when it was running. I searched this site and saw some stuff about stuck vavles - is that a possibility or does it sound like it needs a piston and rings? What should i do? Any advice is much appreciated.