Vintage Dirt Bike Q & A

I recently launched an effort to resurrect a barn-fresh 1974 MT250 that I bought sight unseen on ebay and that has been stored for going on 25 years. I am going thru the ignition system to see why I have no spark. I had the coil tested, no problem. I replaced the points even though the old ones looked hardly used with little to no wear on the heel. The thing I can't figure is that I tried the test with the headlamp in the circuit of the stator to try to find the point that the points open....but the light never goes out....and yes I can see the points open and I gapped them to mid spec (.014)....that gosh darned light....it just stays on as the rotor spins counterclockwise. Do I have a bad stator? I would have done a continuity test on the silly thing when I had it out but I accidentally sat my 47 year old butt on my cheapo Sears tester while I was struggling with getting the rotor off and crushed the durn thing! It is now going on midnight so I can't run out and get a replacement. Please help! Did I mention that I am doing this project with my 11 year old son? I imagine we are going to learn a real lot on this.....

The way the Honda ignition is set up, you have to remove the connection between the stator and the rest of the circuit to use a light. Just unplug the black wire with a white stripe coming out of the engine case.

You also have to make sure both the handbar kill switch and the ignition switch are turned on to get it to run.

Thanks for jumping in to help!

I first checked the continuity of the ignition switch and found it was good. I also disconnected the kill switch (even though it tested fine as well). No spark.

So I hard wired directly from the stator black/white wire to the black/white (primary) wire of the coil. Again, no spark.

So that is when I tried the headlamp test light for checking the opening of the points. I have followed the Honda shop manual directions for hooking it up to the stator wire and battery. But again, the light never goes out! Which leads me to believe that there is a short somewhere in the stator assembly, That is, the path of least resistance is not through the points as it should be and therefore opening the points doesn't make a sam hills bit of difference to the light circuit I set up.

Am I thinking clearly here or have I missed something? Has anyone out there ever dealt with this symptom before?

Thanks in advance for your help. Dan B.

One more thing I forgot to mention....I put a voltmeter on the stator output wire (black/white wire) and kicked it over. The stator is putting out 3 - 4 VAC

Whoops! I made a serious mistake.

Since you have a VOM I would check the resistance with the points opened and closed. closed is just a dead short to ground so you should see 0-.4 Ohm. With the points open you should see 1-7 Ohms from the stator coil.

You will see a couple of Ohms in all circumstances your light *would* always be lit.

I've seen those symptoms when I had a shorted capacitor but I think you will corner the problem when you check for resistance changes.

Your voltage out seems a little low but anything there kind of makes it look like it isn't a shorted cap.

You refer to the "capacitor"....Do you mean the condensor or is there another capacitor somewhere in the stator?

I can't understand how a shorted condensor would affect the test lamp circuit since it isn't actually anywhere in that circuit...

Capacitor and condensor mean the same thing.

It was in response to no spark symptom => you have everything hooked up including the condensor right?
Shorted cap => effectively shorts the voltage going into the coil to ground.

I assume that the capacitor is working since I was able to have the local Honda shop owner / mechanic run a test of the coil on a coil tester and it did produce spark

Any other ideas, anyone?

One more time

Test the resistance points open and points closed for the black/white stripe wire coming out of the case.

You may have a shorted stator coil, you may have faulty points. No one can tell for sure until you test this and report the values.

I finally got my hands on a good VOM and tested the stator resistance. It is less than an Ohm with points closed and about 2 ohms with points open...

Can I still have a shorted stator coil with those numbers? I sure don't know what else can be causing me to have no spark at this point.

Any suggestions?