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Does a 2-stroke Honda CB 100 NE engine need a battery to run? Answered

I have a Honda 2-stroke CB100NE (1018034) engine which I am trying to get working. This is the first time Ive worked with an engine so my knowledge is quite fragmented. So far the engine will turn over using the kickstart but I've been unable to get a spark. Documentation for this specific engine seems to be quite limited but I found a service manual claiming that the generator goes into the battery which then drives the spark plug via the coil, points etc. However, a friend told me that the spark plug can be run directly off the generator/magneto, and since the engine isn't in a motorbike which would require lights and a horn the battery isn't necessary. I'm also not sure how the rectifier plays into this if I'm not having a battery - is the rectifier only there to facilitate charging of the battery?

So my question is, does my engine need a battery to power the spark plugs and if so, do I need to use the rectifier?

Any help would be greatly appreciated. 



Best Answer 5 years ago

The way a magneto works is pretty simple. There is a large magnet on the flywheel of the engine. The magnet passes by a coil of wire mounted next to the flywheel. When the engine turns the magnet passing by the wire generates a pulse of current. This pulse goes to a coil that increases the voltage so it can create a spark. Pretty simple. But the power produce is pulsed to a cycle determined by the RPM of the engine. A light connected to it would pulse (especially an LED) and at low RPM it would be very noticeable. The battery smooths out the pulses so anything electrical will get stead current. Everything is DC current so I don't know why it would need a rectifier. I suspect its actually something else like an isolation circuit to prevent the steady voltage from reaching the coil, unless the coil uses a points system to give the coil a pulsed voltage. The coil needs to have the DC power interrupted in order to generate high voltage. The magnetic field needs to build up and collapse so its generates a current in the high side of the coil. Something like a lawn mower uses the pulse directly from the magneto and does not need any other controls or components.


Answer 5 years ago

Cheers, I managed to get the spark plug working off the generator. No rectifier needed, just a bit of rewiring. Thanks again.

Josehf Murchison

5 years ago

Now if I remember right that one comes two ways, magneto which will run without the battery and the one with a small alternator on the crank that won't run with out the battery.

A pic of the motor would help.