All new parts still no spark

[claerbaut33]

I have a viper 50cc scooter and I have replaced the stator and pick up coil, ignition coil, spark plug, key switch, cdi box, kill switch, and voltage regulator and I still can't get any spark. I have replaced the parts with new in box as well as known good ones and still have no change. I am also experiencing this with a Chinese 125cc four wheeler. Any help would be appreciated I am going crazy trying to figure this out.

[John Kiniston]

Work through the electrical system from the pickup forward.

Are you seeing pulses from the pickup?

[claerbaut33]

I am not seeing anything from the pick up coil. Directly out of the pig tail and I am getting no power out of it. Check my clearance between magnets they're good. Fly wheel is good. New stator and pick up coil and I've tested with a known good one. Have good battery voltage. I am not sure what I am doing wrong or over looking

[John Kiniston]

You need to find a combination of hardware that gives you pulses, maybe the pickup is bad or your magnets are not strong enough.

Test outside the bike engine, you can use a multimeter in ohm mode to read the pickup and compare it to what the printed values are in your factory manual.

You can use your meter in AC mode connected to the pickup to check for voltage, pass and spin the flywheel by the pickup, you should generate some voltage.

[90GTVert]

A bit of an elementary question here, but just in case... These engines can have multiple configurations of stators that will fit, but not necessarily work. Does everything match up to the original, with the same plugs and all?

If you need any clarification for some of the testing :
youtu.be/q9-mr7BXIho

Another thing that is often overlooked is the presence of a kill signal. This is typically a ground applied to the CDI with these bikes, generally via the key, kill switch or side stand switch. If any of those fail, they may ground the CDI and tell it not to fire. In addition, you can have a short that grounds it and causes a no-spark condition. It's easy enough to check. Find a pinout for your CDI and check the kill wire for ground. You should see it ground with the key off or switch set to kill, but with the key on and switch set to run the ground should go away. If you have a side stand safety switch, you'll see a ground when the kickstand is down and it should go away when it's up.

I don't know that that would cause a pickup not to produce a signal. Wouldn't think so... but it's a really quick thing to check.


BTW : I moved this thread into the 4T section. The Viper that I'm aware of is a four-stroke and 125/150 4Ts are most common in ATVs. I can move it back if I was wrong.

[GrumpyUnk]

If the CDI was replaced... did it ever work? Was the old dysfunctinal? Are you sure you have the correct type CDI? There are at least two used in the 139QMB, AC and DC. An AC CDI will produce spark without need of battery power, as there is a coil to generate juice. The DC type needs battery voltage to work.
An AC CDI will work until it is grounded by the ignition key being turned to OFF. If the ignition switch is diconnected using an AC CDI, it should spark when the crankshaft rotates the flywheel. No battery needed.
A DC CDI needs a battery, charged, and the ignition switch moved to send power to the CDI. Disconnect the ignition switch, and it will NOT generate a signal to the coil to make a spark.
tom