1982 mercury 50hp thunderbolt ignition

[Street411]

I have been working on my dad's mercury and can't get it figured out. The motor has a miss, I have replaced plugs and wires with no change. We don't have the manual for it, so I don't know how to test the coils or power pack. Any help would be greatly appreciated.

 

[wrench 3]

Check here for the manual http://boatinfo.no/lib/mercury/manuals/mercury_1965-1989_40-115.html#/164

 

[CharlieB]

Spark test and compression test are the two required test to begin figuring out most every motor problem.

Use the Search and find the 'DIY Spark Tester' This is critical as just holding the plug against the motor cranking and seeing a little spark is not guaranteed enough voltage to ensure it fires once under compression and loaded in gear. The spark MUST BE at least 7/16 inch and hot blue, any less is a problem.

Compression must be at least 100 psi. Many gauges very in reading so the actual # isn't as important as the fact that all cyl's should be close to the same #.

If both of these conditions are good then it is safe to start looking into the carbs as a problem needing a proper cleaning and adjustments.

 

[Street411]

Thank you for the reply and information. I will be trying that. I did test the resistance on the coils. Three tested around 990's ohms and one was 1450 ohms. From the research i've done they should be between 800 and 1100 ohms. Does this sound right? I will post the results of the compression test when I get the tester. Same for spark test.

 

[wrench 3]

For the coil test go to page 215 on the link that I gave you in post #2.

 

[Street411]

Sorry for not getting back sooner. From the test and checks I have done one coil is bad. Part will be here Monday. So I'll let you know then. All others plugs are getting a good spark, 7/16 gap or larger.