1978 Yamaha XS400

[bmxundergrounddotcom]

Hey Guys,

I just purchased a 1978 XS 400. I know it was running six months ago. But, I am trying to get it running and having some issues.

I took the carbs apart and cleaned them out. I didn't pull the needles or jets (I was scared to damage them). I did however clean out the intakes, inside the bowls and diaghrams, etc.

I pulled the points cover, checked the gaps and used some very light sandpaper. Blew them out.

I purchased an in line ingition spark tester, but it doesn't seem to work unless the motor is running - go figure!?!?!?!

So, the bottom line, when I kick the bike, it doesn't appear to spark. When I tried to bump start it, I can hear the motor turning and the compression but clearly no firing.

Any suggestions on where should I start for trouble shooting?

 

[ThePsuedoMonkey]

Definitely sounds like an ignition issue; probably either condenser or ignition coil related. Grab a test light with alligator clips and check each while cranking the engine on the center stand with the power on. Probably easiest to do with a socket to the crankshaft after removing the timing cover.

 

[bmxundergrounddotcom]

Great idea. Should I throw a socket on an impact or a drill and turn it that way?

 

[ThePsuedoMonkey]

You should be able to rotate it with just a 3/8" ratchet, but a drill could work. An impact is probably overkill, since I'd estimate you only need ~25 ft*lbs of torque tops. Keep in mind that these engines are two-cylinders 180 degrees offset, so each only fires every other rotation of the crank.

 

[bmxundergrounddotcom]

Sounds good. I'll give it a try today.

Thanks for your help,

 

[bmxundergrounddotcom]

OK,

After some trouble shooting today, we found that one of the coils is bad. So, I am going to go ahead and purchase two replacements, along with the spark plug wires and boots. I am also going to grab a new condenser and a new set of points. I figure for around $30, it's worth it. I want this thing to run like a top, since it is going to be my daily commuter once it is running.

Is there anything else I should be considering for replacement?

 

[ThePsuedoMonkey]

Good deal. Sounds like you're good to go!