81 yamaha xs400 starting problem

[dan28001]

I have an 81 Yamaha XS400 Special 2. The problem is it won't start but turns over fine. I have replaced the battery, plugs, wires and coils but the right side plug is not getting spark. It has a magneto coil instead of points. Could this be the problem? I have tried to locate one but no luck. Is there a way to test it? It was running before I parked it a few months ago.

[Stratus311]

Break out your voltmeter and check votlage to the coils. The red wire to each coil is what you'll want to check. When everything is ony but not running, there should be 12 volts at the red wire to each coil. Just ground the ground probe on your voltmeter. If there is no voltage to the coil, make sure there are no cut/shorted wires. If that checks out, it could be the iginition module which is bolted to the bottom of the battery box. Hope that gives atleast some direction.

[flynrider]

It has a magneto coil instead of points.

That's a crankshshaft position sensor for the electronic ignition module (a.k.a. ignition pick-up). If the bike is firing on the left cylinder, then it's a good bet that the sensing coil is working. I can't remember if that bike has one ignition coil or two ( I think just one). If it's a single coil and you're getting a good spark on one cylinder, then the problem is not likely in the coil. The most likely cause if it's a single coil is the plug wire from the coil to the bad cylinder, or the plug itself. If it's a dual coil, then it could be either the plug wire or the right side coil itself.

My experience with electronic ignition systems is that they're either working or they're not. It would be unusual for either the crank sensor or the ignition black box to fail just on one cylinder.

[dan28001]

I checked the coils the way it showed in the repair manual and its fine and I also checked the pickup and its fine too. It does have 2 coils. I've looked for the little black ignition box but can't find it anywhere. The rectifier is under the battery or is that the ignition box? I tried swapping the 2 gold relays between the back tire and engine but that didn't work. The only thing I can think of it has a short somewhere but I don't know where to start on looking for it. Shouldn't it be able to fire with just one cylinder? It has good compression and turns over fine but thats all it will do.

[Stratus311]

Did you check voltage AT the coils with the key on? This will tell you if the coils are getting 12 volts. And under the battery is the ignition box. 2 bolts in the rear, 1 L-bracket and bolt up front. If there is no voltage to the coils, then there is definitely a short or broken wire somewhere.

Also, the 2 relays would be for either turn signal, headlight, or safety relay. If one coil works, those are working just fine.

[dan28001]

I retested it and both coils are getting 12 volts. I took the good plug out to test the spark and it gets spark when that T bar makes contact with one of the points in the pick up. I wonder if its not making contact with the other point or if its not working?

[Stratus311]

Well, it should be triggering both sides. Did you try swapping spark plugs to the other coil? If that doesn't change anything, then take the main connectors for the coils, and swap them. In other words, switch the left coil to the right, etc. If that STILL doesn't change anything, check all connectors and try and find a new ignition box maybe.

[dan28001]

I swapped the wires and plugs but still nothing. I swapped the coil connectors and its getting spark but the other side isn't. I adjusted the pickup and its making contact but problem still exist. I hate to buy a cdi but I'm going to have to. I hope I aint wasting good money. Thanks for all the help.

[BuzZz]

Am I mistaken in understanding that your electronic ignition pick-ups and triggers are making contact? This should not be. They should have a small clearance between them, and the specific gap should be listed in the service manual if it is adjustable.

Unless I'm not following what you got properly. (entirely possible, the wife is constantly telling me how wrong I am).

[Stratus311]

Yeah the stator should not be making contact with anything. I would search around for another ignition box at salvage yards or online. If you can pick one up cheap. If that doesn't fix it, then atleast you'll have a spare.