First I want to say hello & that I looked into a few forums before deciding to sign into this one for help & future information.

I recently purchased a used BMX 50 for my son last week. It worked just fine when I purchsed it. I cleaned it up real good the day after purchase and was ready to take my son out riding this past weekend.

The Saturday morning just prior to loading I could not get it started. I checked everything and the problem seemed to be NO Spark. I burned out the battery trying to get it running. I put a charger on it & ran out and purchased new plugs. ( since it only had the old one when purchased)

When I returned, I inserted the new plug & grounded it to the engine & saw spark. Installed the plug & it fired up. We ran it with no problems the rest of the day. It was covered in mud so I hosed it down and parked it.

Now the next morning (Sunday) we went out to ride again. I could not get it started in the morning again. I was not getting spark at the plug again.

I checked the kills.....The handle bar one is in proper position, the brake one seems to work since I unpluged it and the engine did not turn over. The teather one has never been messed with , but I did push it in with my finger and try to start the bike. The remote kill seems to work properly since I tested it (when the bike was running) and it worked as it is supposed to.

So where do I start? Can me washing the bike have anything to do with it? I say that because it gave me problems after being cleaned twice in a row.

Thanks for any help.

 

Yes, water can cause the CDI to stop making spark if one of the kill switches is corroded. Normally water is a poor conductor and won't keep a quad from starting up. Corrosion when dry is also a poor conductor. Mix the two together and you can put enough of a load on the kill switch wire that spark stops.

The kill switch connection stops spark when it is shorted to ground. It allows spark when open.

First verify that the kill switch is the problem. Next time it won't start remove the kill switch wire from the CDI connector (which disconnects all the kill switches). If the quad starts then that verifies this is the problem. And now you have another problem - there is no way to stop the quad engine. You'll have to push this wire back into the CDI connector to stop the spark (and the engine). There is high voltage on this wire so it imperative that you do this carefully with insulated pliers.

You can also try displacing water at the four kill switches by squirting in a little WD-40 one at a time to see which switch is the culprit. Sometimes you can't see the corrosion if it is inside.

There is always the possibility that the correlation between washing and no spark is pure happenstance. If so then the kill switch test above won't pan out. Then we back up and go a different direction...

 

Thanks Lynn!

I want to mention that after being washed off it started and was driven to its resting place. Its the next day that I had trouble getting it started(twice).

I will try what you advised and disconnect the kill from the CDI and see what happens. But, would it not be easier to either pinch the gas line to the carb, or just pull the spark wire to shut it off if it starts? I would think that would be less risky then trying to replace the wire back on the CDI while the bike is running.

I will post back after I try as you advise. Thanks again

 

Don't yank the plug wire to kill the engine. That's not good on the coil. When there is no gap for the spark to jump across the coil output voltage becomes enormous. It can break down the insulation inside and form a carbon path. One that happens the coil won't generate good spark anymore.

You can cut off the fuel, but it will be a couple minutes before you run out of gas in the carburetor float bowl.

The high voltage (which is also current limited) comes from the kill switch pin of the CDI. You could just use a jumper wire. Hook one end up to ground, then shove the other end into the CDI connector at the kill switch pin. That will shut the engine down. As long as the ground connection is solid then there can never be high voltage on the wire (because it is grounded).

 

Ok, I was able to mess with it today & did as you directed. It would not give spark so I pulled the wire for the kills from the cdi plug. It fired right up, so a kill switch or a wire to them is the problem for sure.

So.....Is there a easy way to detect which one is the culprit? Or should I just bypass them and install a toggle for a kill for ease of operation.

The quad is in good shape and runs great, I just don't want to keep dealing with this wiring stuff if I can avoid it.

My thought was to take the wire to the cdi that has the kills wired to it & hook it up to a simple toggle, then into the cdi as normal. I would drill a hole in a proper place and mount the toggle and ground it. My thoughts would be that all kills are bypassed for their troubles, & the engine would be able to start and stop using the toggle.

Is this a option? If not I think the teather or remote is the culprit. But since I could care less about their functionability, adding a simple toggle would act as the same as the handle bar on/off.

Thoughts?

 

You can install your own kill switch, but here are some things to think about:

1) There is up to 350 volts on this switch at fast engine speeds, so you can't use just any switch you have lying around. [The current this switch has to pass is teeny - less than 100 milliamps - so at least it doesn't have to switch both high voltage *and* high current.]

2) The handle bar kill switch is a safety device, and you are proposing a bypass that defeats this. Imagine a stuck wide open throttle. Who is going to be riding this when it happens? Instinct will not allow a novice to let go of the handle bars to reach for a kill switch on the body somewhere.

You have four kill switches on your quad. To isolate which on is the problem disconnect them in the following order while checking for spark:

1) Tether/Lanyard pull cord: Unplug the electrical connector (this is *not* the same as yanking the rubber plug with the cord on it!!!)

2) Disconnect the remote control module.

3) Disconnect the ignition switch connector (4 wires). But this introduces a problem. Now you *can't* start the quad with the start button. Set the parking brake, and make sure you are in neutral. Short the starter solenoid posts together with a screwdriver to force the starter to turn. Do you have spark now?

4) Disconnect the connector feeding all the handle bar switch functions. This includes headlights, start button, and kill switch. Once again the start button will not work. Short the solenoid posts again (while the parking brake is set and you are in neutral). Do you get spark now when shorting the starter solenoid posts?

If all four kill switches are disconnected and you still don't get spark then you have a short to ground (pinched wire) in the wiring harness somewhere.

 

Thanks Lynn for all your help. I just may go through that process to find out what the problem is. I also may just go ahead and install my own kill anyway.

The way I am considering doing it is to still utilize the kills function or lack there of. I will get the best switch I can for this need. I will take the wire that runs to the cdi and run it to the switch. Then wiring it back to the original pin wire to the cdi. I will mount this swith up front on the bike somewhere as close to the handle bar on/off as possible.

My thought is this.....Being that the kill problem comes and goes, this will overide it if needed. This switch will alow me to manually overide the kills with a quick switch when needed, & the normal handle bar on/off would work as normal with the switch open. But if it shorts out again, close the switch and the bike will start and run as normal. Close the switch & the bike would shut off, being the kills are telling the bike to shut off full time.

This will allow my son to be able to ride until I identify the exact problem and get the part and install. Plus if ever in the future another kill problem occurs I will be able to identify that it's another kill switch problem right away, yet not get stuck when out riding and have to tow a bike home.

Again, thanks for all your help. I will follow your directions on finding the exact problem also.

I will report back on what I did & found so to maybe help someone too.

 

Your plan sounds good to me .

 

I picked up a switch (20A 125V Double Insulated Interuptor) at the hardware store for 6.00 yesterday. Took me about 20 minutes to complete. I snipped the wire to the cdi leaving a 3 inch tag with the original pin connector on. Then I took some wire(better than whats on the bike) about 8 inches worth and connected it. Made the same length connection wire to the wire that leads to the cdi. I connected that to the switch, and then from the switch put the pin back in the cdi plug. Plugged in the cdi and re mounted the cdi. Drilled a hole in the plastic to mount the switch and install, DONE!

Works perfect.

Now I no longer have to be concerned with the constant kill switch issue that these bikes seem to have or get. It was my way of bypassing all that extra wiring stuff that seems to cause lots of problems.

Now, the teather kill, and the remote kill are not working. But I never used them anyway, just needed to be able to get the bike to operate for my son to have some fun. He does now!

 

I just repaired one of these for a friend. It ran great aroud the yard. I used the kill switch on the left handlebar to shut it off. It would not re-start. No spark. When you use the kill switch to shut it down, you must push the switch in once which apparently either resets the switch or there is a problem in the switch.This worked every time I needed to re-start. If I didn't push in the switch it wouldn't start. I hope this helps you out. Steve