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250ex weak spark issue

6371 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 sir are a genius. the observation that both wires from the starter should not be hot made me rethink the whole thing as a spark issue. since the neutral light wasn't coming on I decided to investigate the neutral safety switch. I wan't sure how to properly test it so i bypassed it using a write-up on another forum. It wasn't as simple as wiring the two safety switch wires together, but it was pretty easy. Now i have a nice hot spark and the starter works with the button, and i will be able to start it in gear now. I sprayed some starter fluid in it and it started for a second. im going to overhaul and rejet the carb, add a uni filter, adjust valves, change oil, diff fluid, and swing arm bearings before i ride it....its a $250 quad and needs more work to be up to my standards.

If anyone is experiencing the following condition this is EXACTLY what it looks like and how to fix it.

-starter button does not engage starter
-neutral light does not come on when quad is in neutral
-no spark when crossing the solenoid to engage starter
-weak spark at the beginning and end of "pull" when pull starting

easily test by removing the main fuse and pull starting it with the key on, if you now have a good spark reinstall fuse and follow this write up to bypass the neutral safety switch.

*copied from another site**

You will need 2 pieces of 18/20 guage wire, 2 male spade connectors, 1 female and 2 male bullet connectors.

The neutral switch located inside the engine case provides the ground to energize the neutral light, and the starter relay, when the quad is in neutral. All that is needed to get the quad to start in any gear is to provide a permanent ground bypassing the neutral switch. The only problem with that is the neutral light will always be energized. We can modify that too.

I'm sure there are other ways to do this but this was the simplest way i could find without unwrapping more of the harness, and i also wanted it to be reversible.

Remove the seat, and the left side cover. Behind the battery, laying in the tray there is a section of wiring harness taped up that comes to an end. Mine was wrapped in Blue tape at the end. When you unwrap the end you will see a connector with a plug in diode. The light green w/ red stripe wire comes from the neutral light. The solid light green wire goes to the nuetral switch (ground). As a benefit you will also see 2 unplugged bullet connectors which happen to be for accessories. ( Like maybe a brake light

Unplug the diode. With one wire, connect a male spade and plug it into the solid light green wire. The other end connect to a ground. I used the green accessory wire with a male bullet connector for ground, but you can ground to the battery or frame if you like. That is all that is needed to start in any gear. The downside to this is your starter button will always be hot, so if you accidently hit the button the starter will engage.

Now to get the neutral light to function properly you need to connect the neutral light (light green w/red stripe) directly to the neutral switch. On the left side frame rail, in front of the rear fender, the wiring harness runs through, and there are a number of plugs attached to the frame rail. There are also 2 wires with bullet connectors that run along with the harness here. one is solid light green (neutral switch ground). Disconnect it. With your other piece of wire, attach a male spade and plug it into the light green/w red stripe at the diode. Run it out with the harness and connect it (with a male bullet) to the solid light green wire at the frame rail. The other end i just used a female bullet and melted the end closed to cap the wire. Now the neutral light will work as it should.

I also used dielectric grease at all the connections and rewrapped the harness at the diode.

Also I'd like to say that I don't endorse anyone modifying the electrical system on there quads. It could cause unforseen problems in the future. If you do, you do so at your own risk.

That being said, I've been running with this mod for a couple of months with no problems. I also have a similar mod on my utility, and have been running it for 3+ years with no ill effects.
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