Need your help on an issue I'm having with my 1985 Yamaha Moto 4 YFM80N. It had sat in my garage for about 10 years and was running like a champ when it was put up. 3 years ago I had pulled it out, cleaned it up, rebuilt the carb, changed all the fluids, put a new battery and new tires on it, and had it running again. I put it away yet again, and am now trying to get it going again to sell it to a friend of mine. It's got a brand-new battery in it, since I didn't store the other one properly when I put it up 3 years ago.

Here's what I know so far:

- the "neutral" light comes on bright
- the engine turns over at normal speed when the electric start is used
- definitely getting fuel
- When I ground the spark plug to the chassis and turn the engine over with the starter, it'll spark once right after the engine starts turning over then not spark again.
- The single spark I am getting is strong (white/blue).
- I'm seeing voltage fluctuation from the pulser coil when I spin the starter and check the voltage at its terminals
- I'm not sure how the check the CDI unit (no manual), but when I hook the voltmeter up to chassis ground and the orange ignition coil lead and spin the starter, I see some occasional fluctuation but not as much as I would imagine it should be putting out.

I initially thought it may be the coil, since I'm getting output from the pulser and getting one single spark. Then I started thinking it was the CDI unit not sending voltage to the igntion coil.

I've got a new coil on its way, and am hesitant to purchase a CDI unit since they're $140. Anyone have any ideas about anything else I should investigate before I spend my cash? I need to get this thing up and running before Christmas so my friend can give it to his kid.

Appreciate the help!

 

Anyone have any thoughts? I'd appreciate any help I can get!

 

Just as a follow-up, I was able to finally solve the problem with my moto4. The CDI box was shot. Swapped a new box onto it, and the plug fired repeatedly and strong. Starts up and runs like a champ now.

Just wanted to close the loop in case someone else had a similar problem.

 

glad to hear you got it fixed.