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Discussion Starter · #1 ·
I am new the whole mechanic field so i have no idea what is wrong, nor do I know the proper terminology for alot of things. problem: 1980 CM400A has been working fine for the whole time I've had it. now though, it starts just fine, it even goes. but i can't make it go past about 15 mph, and that is after working it. it wants to just cruise at about 3 mph. Now I just replaced the spark plugs, thinkingthat might be it, but no go. My frienddid this little thing where he unscrewed the plugs, put his finger over the hole and told me to hit the kickstart. one of them made a whooosh sound and the other made no sound at all, to which he made a frownie face to. I NEED to get my bike fixed so I have transportation again, and I am all set to just start taking it apart piece by piece hoping i can find an obvious problem, but really I have no idea what I am doing. Also of note, when the back tire is off the ground, it looks like it gets just fine rpm when revved. I hope someone can help me with what little i am able to tell.
 

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No compression could mean several things. A valve could be bent or not sealing, the rings could be shot, or there could be a hole in the piston. A test with a compression tester is a lot more reliable than using your thumb.

You can also check and see if you are getting warm exhaust in both exhaust pipes to determine if one is not firing. Just be careful not to burn your hand when testing the pipes.
 

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Discussion Starter · #4 ·
ok.... seems to remind me of what my friend said... so is it more practical for me to try to fix engine, scrap it, or scrap bike? and if fix, where do I start? by the way thank you guys so much.
 

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Figure out what's really wrong with your engine. If it's simple parts replacement, do it. If it needs a new engine, part it out. People are always looking out for parts for older bikes.
 

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Discussion Starter · #7 ·
so I did some research on the schematics. Now I have a fairly moderate grasp of what I'm talking about. I got the cover off the cylinder head, and inside there were like 8 bolts or something, one of them was not on at all and jsut sitting inside there. I put it back on but my friend said it is a very presice thing and i need the specs for them? any chance one of you can help with that?
 

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Did you take off the cylinder head or the valve cover? If one or more of the of the camshaft bolts, head bolts or valve bolts were loose, that would explain a lot.

The valves should be adjusted to spec for the proper amount of free play and all of the bolts should be tightened to the proper pressure using a torque wrench to check them. You may want to check the manual to see if they suggest loc-tite for the bolts.
 
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