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250ex weak spark issue

6372 Views 3 Replies 2 Participants Last post by  ktriebol
Hi everybody, i'm a long time member but got locked out of my old account so had to make a new one. I just pickled up a non-running 01 250ex with a weak spark issue. I went through the wiring harness with a fine tooth comb and greased every connection and cleaned the grounds. I also rebuild the kill switch and tested kill and ignition switches. I also reseated the plug boot to the wire to ensure a good connection. I tested the spark with the plug and a spark gauge, so i know the plug is not the problem. It has a new battery, the electric start does not work, but i'm getting power through both wires from the start button to the solenoid so I assume that it is just solenoid problem and can be dealt with later, when I cross the solenoid the starter engages. the indicator lights do not come on when i turn the key but the headlight comes on and the ignition switch and kill switch are both working. When i pull start it i get a very weak spark, about 1 yellow spark every 10 rotations. I'm no stranger to small engine repair but wiring is my weakness. My question is, what would cause a weak spark? Since i am getting a little spark I think that might make it easier to diagnose. I'm guessing stator/pulsar coil. could the ignition coil cause a weak spark? CDI? voltage regulator? Im hoping someone who has solved a similar issue can chime in. luckily parts are cheap for these bikes. Any help would be greatly appreciated! I ordered a manual.


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You say you have a spark issue, but you discuss a spark issue and a starting issue. It would be better to have two posts, one for each topic.

Yes, I think that if you have a weak spark, the problem is probably coming from the CDI unit or the ignition coil. Honda CDI's usually send 100 volt pulses to the ignition coil. Can you measure the input to the ignition coil to see if you have 100 volt pulses? If so, your CDI is good. To test the ignition coil, the best way is probably to replace it with one that is known to be good.

You say you are getting power through both wires from the start button to the solenoid. This confuses me because there is only one wire that goes to the solenoid (starter relay) that should have power. There are two small wires on the starter relay. One is green, and the other is some other color. The non-green wire is the one that should have power. If the green wire has power at the starter relay, that explains why your electric starter won't work. The green wire is your ground wire and should read 0V while starting as long as the transmission is in neutral. 12V at the green wire indicates that it is broken somewhere, or there is a problem with your neutral safety switch, and you don't have a complete ground circuit, thus the starter relay won't work. If that is what you have, then you need to find out where you are losing ground in that green wire.
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Excellent. I'm glad you got it running. Naturally, the best thing to do now is keep your neutral switch problem in the back of your mind, so that if and when you ever have to open your engine up, you can replace the neutral switch at that time.
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