Yamaha qt50 no spark

So when I moved into this house, there was a bike in the back shed that the landlord said was left behind like 5 tenants ago. The registration sticker on the plate expired in 87 lol.

I spent the summer cleaning and rebuilding her and now I'm seeing zero spark. I think I figured it out but jus looking for some info.

The battery is showing 6.4v, and then the hot wire splits off.. one goes into a harness through the frame so who knows where that goes off to lol, but the other ties into a little black matchbox sized thing with polarity and a diode symbol. Not sure what it's called, bit seems important.. When I go from pos. To the frame I see 6.4v, but when i go neg. To frame i see .8v.. so i wanna say my issue is this voltage restriction right off the hop. When I ohm it out my meter shows OL which doesnt make sense cause I saw .8v with power but maybe diodes are tricky..

So basically I just want affirmation that having .8v through the diode is a problem..or is that what it's supposed to do. I dont know where the other wire is going but it should be carrying 6v to a coil or something down by the spark plug.

Side note- I'm seeing a solid 6v from the wire that connects to the spark plug to the frame.. should that be steady voltage or should that be like a pulse to spark the spark plug in sequence? Not sure how the firing system would work either but that also seems fishy to me..


Re: Yamaha qt50 no spark

Re: Yamaha qt50 no spark

That little black thing is a rectifier which changes AC to DC to run your Direct Current loads. The rectifier is not necessary to run the engine ( I know as I have one that I am restoring and it runs fine without it) .Concentrate on other areas such as broken wires coming out of magneto , bad connections at any harness plugs, especially behind headlight from ignition switch, and get resistance readings for charge coil and pulse coil. There are operating ranges for both coils but I don't remember readings.

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