1969 1000 merc 100 hp ignition

[rockpile]

Would the distributer cap or plug wire be the only place to be the cause of no spark on #4 cyl?

 

[emckelvy]

Re: 1969 1000 merc 100 hp ignition

You might want to unscrew #4 plug wire from the distributor cap and check it out carefully. Any problems will typically be at the ends. One thing I've found is a bad plug wire that'll pull away from the brass crimped-on screw-in ferrule at the distributor. Actually a good tug at the wire while it's screwed into the cap would tell you a lot.

You can also check the wire with a meter to see if it's broken internally. These are solid-core wires so the resistance should be well below 1 ohm.

Pull the cap and check for debris which could cause cross-arcing or other problems with #4 contact.

Check for obvious cracks or arc-marks in the area of #4 contact inside the cap.

Worse case, if another, known-to-be-good plug wire won't fire in #4 contact, I'd replace the cap.

HTH & keep us posted........ed

 

[rockpile]

Re: 1969 1000 merc 100 hp ignition

I pulled the cap, checked the wires, inside of cap was a little dirty, cleaned it up still no spark on #4. Switch box maybe? Without the suit case tester is there another way to check it?

 

[Laddies]

Re: 1969 1000 merc 100 hp ignition

The suitcase tester is a joke here is the best test from CDI

If the wire is OK it has to be the cap, just make sure the wire is not shorted to ground as the cap is pricey

 

[rockpile]

Re: 1969 1000 merc 100 hp ignition

OK, so I've done this and got spark on each cylinder individually. I essentially replaced the trigger by doing this right? Soooo, I must have a bad trigger?

 

[emckelvy]

Re: 1969 1000 merc 100 hp ignition

Not necessarily. If you have spark on the 5 other wires I don't see how the trigger could be bad.

The trigger works by having the "chopper" disc go past it. There are 6 openings which provide the trigger points, if I recall this is "Hall Effect" type of ign but I can't remember whether passing the solid part of the disc or the hole by the trigger makes the spark.

One thing you might do is, with the coil wire unscrewed from the cap and reinserted into the coil, and the cap removed, see what kind of sparks you get directly out of the coil wire. If you get six sparks for every revolution of the distributor there's nothing wrong with that trigger.

You wouldn't even need to take the belt off to do this, just use a ratchet & socket to turn the flywheel. Take all the spark plugs out to make the engine easier to "bar" over.

Note if you had intermittant spark on the other 5 cyl's then I'd suspect the trigger but otherwise you've got something else going on I think!

Keep us posted, this is a curious one!

 

[rockpile]

Re: 1969 1000 merc 100 hp ignition

So i've done the spark test as described by the CDI chart. It sparks on each one individually as the rotor is aligned with each cylinder. This indicates a good cap, right? I've switched plug wires, the problem stays at #4. I also have intermittent spark on the rest. Running voltage is 12.7 volts at the red terminal on the switch box. I also unscrewed the coil wire and turned the flywheel as suggested, I only got 4 sparks per revolution. Can the distributer be the problem? Thank you for any suggestions.

 

[emckelvy]

Re: 1969 1000 merc 100 hp ignition

Sounds like a bad trigger!

 

[rockpile]

Re: 1969 1000 merc 100 hp ignition

I've got a line on a whole distributor. What are the differences? Mine has a tan cap that is screwed on, this one has a blue cap and band holding it on.