No spark on 20hp Mercury

[madmarlin]

I have a 20hp Merc pull start Serial# 9565190 Mid 80's model I believe. I'm not getting any spark on either plug, have changed plugs, leads, and coils, have tryed disconnecting kill switch and still no luck. Have checked all wires and connections and all seem fine, so am thinking Stator or control box. Question is is there anything I can do to check these before going out and buying replacements or is there soething else I haven't checked yet. Thanks in advance.

 

[Rabbitdawghunter]

Re: No spark on 20hp Mercury

I would first go to the CDI module and disconnect the black with yellow tracer wire. That would eliminate all problems with the kill stop circuit. You also won't be able to shut the ignition off if spark is restored by doing this so be prepared to ground this wire to the block if necessary. Further testing will require a DVA adapter for your multi-meter. The generic specs that work with most outboards are 100 plus volts from the capacitor charge coil, .7 to 15 volts for the trigger. Don't forget to make sure your ground to the cdi is making good connection.

 

[madmarlin]

Re: No spark on 20hp Mercury

Thanks Rabbit, have disconnected the black and yellow kill switch circuit and tried pulling over with spark plugs grounded to the block and still no spark. Have cleaned all ground connections, could u pls explain A DVA adaptor a little more or is this something the local Mercury dealer could do for me. A little more history, I origanally bought this motor for parts but found didn't need much to get going again as all parts were there. once back together I pulled it over and it started second pull then died and won't start again, is it common for a stator or control box to just die like that.

 

[Rabbitdawghunter]

Re: No spark on 20hp Mercury

Some of the other guys on here can probably give a much more accurate and technically correct description of a DVA (Direct Voltage Adaptor)but I'll give it a shot. Every time the magnet mounted on the flywheel passes by either the Capacitor charge coil or the battery charge coil(both encased in the potted material of the stator)voltage is created. If you were to look at this represented as a line oscillating back and forth from pos to neg it would look something like a heart monitor. The peaks would represent when the North pole of the magnet passes the coil and the valley when the south pole passes. If you tried to measure this pulsing voltage with multimeter it would just be a mad scramble of numbers because the values are changing so rapidly. The DVA just measures the very peaks of the voltages so you get a reading that you can use. The DVA is about 60.00 dollars and the manual that you will need is about 75.00 if you buy it new from Mercury. You may be able to find it on EBay for much less. It will probably make more economic sense to just take it to a qualified mechanic at least for the diagnosis.

 

[andy6374]

Re: No spark on 20hp Mercury

The combination of the stator and flywheel produces an AC current, AC volage. A regular multimeter (VOA) can't measure the peak voltage that well and what it does give you is the rms voltage. The DVA adapter enables you to measure the peak voltage and this is the voltage which is important. You can get the peak voltage measurement by multiplying the rms voltage by 1.41 (square root of 2), albeit it will be a little in accurate.<br /><br />You could start off with some resistance tests between different stator coils and trigger coils. If these don't check out then you know one of them needs replacing, but just because the pass the resistance tests doesn't mean they're ok. Remember you need the peak voltage readings.

 

[madmarlin]

Re: No spark on 20hp Mercury

Thanks Guys, As you suggest is not viable for me to buy at this point in time thus I have taken motor into work shop for testing when Mechanic gets around to it then hopefully I will know for sure what is wrong. Thanks again and will let you know how I go.

 

[andy6374]

Re: No spark on 20hp Mercury

I didn't try to suggest that it is not viable for you. Get the manual and the DVA if you plan on working on your motor in the future, use them once and they have paid for themselves.

 

[madmarlin]

Re: No spark on 20hp Mercury

Thanks andy/rabbit, got motor back from mechanic and he tested cdi by trying another one he had there guess he hasen't got a dva, looks like cdi is gone so up for another when wife gives me the cash.