79 xs 400 no spark left side

TheApprentice

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Hey guys, I’ve been doing some troubleshooting on a 1979 XS 400F. I’ve tried the following: New spark plugs, swapped coils left for right, checked for continuity, new battery, tried adjusting points, right side works fine but left side no spark. Looking for advice, thanks in advance!
 
Welcome!

Does the right side points spark across the contacts if you manually open them with the ignition on?
I hadn’t checked my emails since I posted this thread, so I didn’t get a chance to test it manually. However I got it running, even though for only 30 seconds since my dad, who has been helping me thus far, said that it was only firing on one cylinder and turned it off. The contacts were still dirty, so I probably didn’t clean them properly or enough. Now I just need to figure out why it is only firing on one cylinder even though there is spark on both sides. I can link the video of it running, if I knew how too. I will keep in mind to check it manually if I have a similar problem again, so thank you!
 
If you have spark on both sides now, the cylinder is not firing because it has low compression or because it is not getting fuel from the pilot circuit of the carb on that side.
 
If you have spark on both sides now, the cylinder is not firing because it has low compression or because it is not getting fuel from the pilot circuit of the carb on that side.
we have fuel coming in since the cylinder gets wet and the valves work, it fires at a higher RPM and suspect that it’s an ignition timing problem
 
I would rent or buy a cheap compression tester and see where that stands and maybe check/adjust the valve lash to ensure the engine is healthy. Anything over 100 psi should run, but the higher the better and the cylinders should be within 10% of each other.
 
I would rent or buy a cheap compression tester and see where that stands and maybe check/adjust the valve lash to ensure the engine is healthy. Anything over 100 psi should run, but the higher the better and the cylinders should be within 10% of each other.
I think we might have one, I know we have a timing light since my dad had a timing or carburetor issue with his vmax before he sold it. Also I’m probably gonna start a notebook of all the specs that I’ve found for the xs so far. Just to check while I’m doing any maintenance on it before I upgrade to a larger bike later on. It’s my moms old motorcycle that my dad got for her so they could ride together. Thanks for the help though, after my dad gets home from work I will see if we can test the compression.
 
I think we might have one, I know we have a timing light since my dad had a timing or carburetor issue with his vmax before he sold it. Also I’m probably gonna start a notebook of all the specs that I’ve found for the xs so far. Just to check while I’m doing any maintenance on it before I upgrade to a larger bike later on. It’s my moms old motorcycle that my dad got for her so they could ride together. Thanks for the help though, after my dad gets home from work I will see if we can test the compression.
I might not even need to get a larger bike, there is an XS400 on Kijiji that looked pretty nice.
 
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