Ignition problem Classic Fifty.

Like the title says I have an ignition problem. The last time I was troubleshooting a problem I saw a chart in CDI ignitions website with resistances and voltages for all Mercury engines. I had a '74 850. What I'm asking is where to find a chart with resistances and voltages for an '88 Classic Fifty. The top cylinder doesn't reduce RPMs when I pull the plug wire off, all the others do. Thanks

Hi, Alex, check out the CDI Electronics online troubleshooting manual; the section for ADI (Alternator Driven Ignition), like your '88 Classic 50 has, starts on page 101 of the manual.

https://issuu.com/cdielectronics/docs/7th_edition_troubleshooting_guide/102

The last few ADI motors I've worked on have had bad ign coils. They like to crack and then will arc/fail. You can pull the coil, remove the mounting cover then peel back the rubber and check for cracks all over. You can also do resistance readings with a meter.

Another possibility with a single-cylinder dropping off is a bad ignition box. But be sure to do all the checks first before condemning the box.

You can also swap coils and see if the problem follows the coil.

HTH & let us know what you find.........ed

Thanks Ed. The first thing I did was check the compression, OK, then the spark with a test plug, semi OK. The spark was very thin and there was a yellow part in the middle. I went to the lake Tuesday and it started and ran on all 4 cylinders. I even caught some bass. The only problem is the idle is too low and I'd like to check the timing but don't know which screws to adjust for the idle and timing.

Here's a good video from this site on ignition coils:

https://www.marineengine.com/videos...il&utm_term=0_33e29cf73c-c51eacdde4-352422949

One old trick you can try is to install an electrode-type spark plug in the suspected cylinder. This type of plug takes less energy to fire than a Perma-Gap. Set the gap at around .025" for testing purposes. The Champion L77JC4 has the correct reach and heat range for your Classic 50.

If it idles and runs better I'd suspect the ign coil. Swap coils and see if the thready spark transfers to another cylinder.

You should have a manual before attempting any timing adjustments. The screw for that should say "Spark Stop" or similar. Don't touch the "Throttle Stop" unless the carb butterflies need adjusting.

Idle speed is controlled by the "Idle Stop" at the throttle arm/manifold cover. Screw the screw against the throttle arm to increase idle speed. You may have to adjust the throttle cable after making this adjustment.

You'll need to have enough preload on the throttle cable so that it pushes the throttle arm gently against the stop, when you return the remote control to Neutral.

Keep in mind that your cranky ignition system may be the cause of a low idle. I would address that issue before making any other adjustments.

HTH........ed