Low compression. Please help diagnose!

i have a 1994 XR250R that stopped running recently.  i had been riding for about a half hour when the bike died on me like it ran out of fuel.  it hasn't started since.  actually i was able to jump start it down a pretty good hill but it ran like complete shit and i had to keep it pinned just to keep it running.  it felt like it was only firing once every couple cycles.  There is plenty of good fuel in the tank and that fuel is making it down to the carburetor.  i rebuilt the carburetor a couple months ago and its been running great since, so i dont think thats the issue.  i checked and i do have spark and the spark plug is not fouled, i replaced with a new one anyway.  my air filter could be cleaner but not clogged at all.  my decompression cables are disconnected.  The bike is leaking oil significantly at the head gasket which im thinking is probably the issue.  i did a compression test with the engine cold and after first kick i had 60psi and after about 10 kicks or so it gradually made its way up to 150psi.  my manual says it should be between 185-213psi.  This made me further believe that it is most likely the head gasket.  i then added some oil into the cylinder and redid the compression test.  first kick was 60psi again and it gradually rose over 10 kicks or so to 190psi.  My service manual shows this to mean that my piston, rings, and/or cylinder is messed up.  what do you think?  will a bad head gasket stop a bike from running?  I'm guessing at this point its probly the head gasket that got so bad that while riding it caused the bike to reach such low compression that it couldnt fire but that i also need new rings on my piston which is why the compression test improves after adding the oil to the cylinder.  Does this sound right?  am i missing anything else?


how difficult is it to replace the head gasket yourself?  how much more work is it to do the piston and/or rings?  


Thanks a lot for any input, i want to get back to riding!!!

First off you'll need a good manual "factory is best".  Sounds like your head gasket is the problem.  And yes, the head gasket is a vital part in making compression along with a good bore, rings, and valves. 


As long as you take your time, take pictures along with good notes it is something a normal person can do on there own.

You can't really do a proper compression test on a bike with an auto decompressor, it just doesn't work. 


That said, the leaking oil is definitely a problem, you will need to change your head gasket.


While you are at it I would put in a new piston, or at least new rings, and maybe change the timing chain, just given the age of the bike.


On a scale of 1 to 10 it is a 5. Not very hard or technical, but you do have to work carefully, cleanly, and not make any mistakes.


If you haven't had a 4 stroke motor apart that is a great motor to learn on.


Where in CA are you?

Your engine is tired and worn out. Not running is it's way of telling you it needs some attention. You're right, your head gasket needs to be replaced, along with probably the rest of the top end. Good luck to you.

Thanks for the feedback guys! I'm looking forward to the project. It is a little more in depth than I've worked on an engine before but I'm confident I can do it. I'm low on spending money because I just bought a plated xr250r last weekend with a busted top end for $300. Came with a Baja designs kit and super trap exhaust, I'm pretty psyched on the deal. I'd like to do the full rebuild with piston, rings, chain, and head gasket but I'm gonna have to wait and save up money. I'm temped to just fix the head gasket and ride it till I have the money to do a more elaborate rebuild. Is that a bad idea? I live in Cameron Park 30 mins east of sacramento, how about you Mudguy?

A pic of my bike:

ImageUploadedByThumper Talk1378427079.285120.jpg

And the new plated bike:

ImageUploadedByThumper Talk1378427153.013599.jpg

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