Ignition problem

[daithesailor]

I have a problem with the ignition system of my Yamaha 4HP two-stroke outboard; Model number 4ACMH.

Basically there is no spark and so far I have ascertained the following:
Ignition coil secondary - resistance 2.4kohms
Ignition coil primary - resistance 0.5ohms

The above measured with a Fluke digital multimeter.

Connecting an analogue volt-meter to the feed to the coil, coil disconnected, shows an increasing positive voltage then a sharp fall and then a decreasing negative voltage as the engine is rotated.

The coil secondary resistance is about what I would expect but, in my experience, the primary resistance is in the order of a few ohms.

Can my figures be confirmed and any other advice to fault find the lack of spark would be appreciated.

Many thanks

David

[rodbolt17]

check the pulsar coil,charge coil and make sure the stop switch is working correctly.
your ign coil resistance numbers look good.

[DeltaDawg]

You don't indicate what year it is so I can't pick the right one off the chart but from the chart that came with my Yami peak voltage adaptor which is really manufactured by CDI electronics. The chart indicates Yami 4hp, 2stk, 1984-1999, stator 250-300 ohms, 100 dva, check points brown-black, trigger 30-36 LS ohms red/white-black 280-340 HS ohms white/green-black, ignition coil 0.1 ohms primary 3.1 kohms secondary. I found a spark checker helpful when diagnosing my ignition problems, the inline one from Harbor Freight was good used in low light so you can see the light but you have to grind down the tip to fit your spark plug cap and make a bushing out of a connector for the pig tail's cap. My problem ended up being the charge coil so I had to replace the stator and from what I read that is a typical problem for a 10 year old engine but like Rodbolt wrote I checked the kill switch and key switch while doing diagnostics to make sure the problem was not there. Your Fluke is a nice meter, I just have the Harbor Freight automotive diagnostic meter but the peak voltage adaptor's base plug's pin spacing fit my meter fine. The CDI chart that came with the adaptor said to use a shielded meter, your Fluke probably is shielded. The chart also indicated use of a piercing probe but I was too timid to do anything to break the insulation so I took my readings "open' cranking, probably awkward if yours is a pull cord starter but I watched some You Tubes of guys get the readings while pulling the cord. Good luck I had fun diagnosing and fixing my problem but I had time to work on it and I enjoyed getting some new tools.