CDI problems (experts needed)

[hect75]

Hello,
I need your advice with electrical troubles. The Vento was running perfect last Friday. Today, like everyday I turned the Vento on but after letting idle for some minutes (less than 5) the Vento turned off. I drained the carb, check the spark plug and let it rest for 30 min. Again, it turned on but after a couple of minutes it turned off. I am thinking could be the rectifier or CDI because once the ride gets hot, it turns off. I will check on youtube how to check both (rect + cdi) in case the problem is some of these guys. What you guys think about it?

I will appreciate any helpful advice.

[SpudRider]

A bad rectifier will not cause your engine to turn off as you described.

If the engine stops running you might have either an electrical problem, or a fuel problem. Do you have a good spark? The easiest way to check the CDI unit is to substitute a spare CDI unit.

[alchemysa]

Get a new plug and eliminate that as a possible problem. Even better, buy 2 new plugs from separate stores. I went through about 3 plugs in a fortnight. I'm sure there was a bad batch of NGK's floating around.

Plugs can look OK when tested but fail under compression. You should have a bright white or nearly white spark at the plug. A piss weak blue spark is not good enough.

[katoranger]

I second the sparkplug. They will give those symptoms if going bad. Cheap too. Then I would suspect the CDI after that.

[Weldangrind]

Please let us know how it runs after installing a new NGK. We can continue diagnosing from there as necessary.

[hect75]

I measured resistance of CDI and rectifier yesterday with the voltmeter, they´re working. However, I learned that the ignition coil is not working. I removed the spark plug from the engine and tested out for sparks. No sparks from the plug when pressing the on button. I removed the ignition coil (i.e., under the tank) and measured in Ohms (primary test) got 1.5. Then, measured the secondary test with no reading. I concluded by visual observation (no sparks) and readings the problem is the ignition coil. I ordered this guy for around 7 bucks but will wait until Vento confirms the order. You guys think could be the ignition coil? any other test before concluding the problem?

By the way, the spark plug is NGK it has only 50 miles of use (recently changed the oil and spark plug).

Kind regards

[stretch8668]

Did you have plug grounded to engine when tryed it and I was thinking it was coil. Try starting bike wait til it dies and ground plug if no spark then I would suspect its the coil also look for cracks on coil if there are any that'd be what it is

[hect75]

Originally Posted by stretch8668

Did you have plug grounded to engine when tryed it and I was thinking it was coil. Try starting bike wait til it dies and ground plug if no spark then I would suspect its the coil also look for cracks on coil if there are any that'd be what it is

Because there is no spark, the moto does not start. I grounded the plug to engine when tried. The coil looks new (it is 8 years old) but the reading is below the average of 3-5 Ohms (1.5).

[Weldangrind]

I've had brand new coils with bad primary windings and others with bad wires. If you examine the plug wire where it exits the coil, you'll find a rubber boot that seals the wire. You can peel the wire back and then unscrew the wire completely from the coil body, and you can also unscrew the wire from the plug cap. Once the wire is free, you can measure it and the cap individually.

[hect75]

I will, thanks for the tip.

[hect75]

I replaced the old ignition coil for the new one, I tried and started, it is running again. I will ride it and see what happen.

[Weldangrind]

Have you removed the coil wire from the old coil for testing?