'77 Merc 1500-Fix a faulty trigger?

[eggs712]

Hello, I have a 1977 Merc 1500 with ignition issues. I replaced a bad trigger on it before winter with a used one from eBay and had the motor running perfect after also fixing some fuel issues.

I took it out this weekend during spring break and for the first two days, the motor ran perfectly. However, midway during the third day, the motor completely cut out without warning while I was leaving my campsite. It wouldn't start again and after 30 minutes of trying to start it back up, I had to use the trolling motor to get back to shore. The next day, it started again but then completely cut out again while warming up in high idle and wouldn't even try to start again. So I pulled the spark plugs and they weren't wet or fouled. Primer bulb was hard. I then checked spark and found no spark on all cylinders. I cleaned out the distributor cap (wasn't very dirty) and still had no spark.

I haven't taken the time to run through the tests to confirm it, but I'm betting that the used trigger is already out.

Is there any way to fix those old triggers? I noticed that the copper trigger disk was somewhat corroded, so I'm wondering if something as simple as replacing that disk would fix it. Thanks in advance!

 

[wired247]

Re: '77 Merc 1500-Fix a faulty trigger?

The disk just breaks a magnetic field in the variable reluctor trigger which in turn causes the transistor ( switchbox ) to close and allow current through the capacitor ( other part of the switchbox ). Corrosion on it does not affect how the trigger works. The wheel is just a screen. The original variable reluctor set can be replaced with a Hall effect set that DCI manufactures. It uses a steel plate instead of the factory bronze plate. Works under a different principle but opens the transistor just the same. In any case a friend with an oscilloscope is a good thing.

Personally, I'd be looking more at the switchbox.

 

[eggs712]

Re: '77 Merc 1500-Fix a faulty trigger?

Thank you very much for that knowledgable answer, wired. I was curious how the trigger actually worked. I'll use the CDI testing procedures to see if it's the trigger or switchbox.

This time I'll fork over $300 (yikes!) for a new CDI trigger if that's what's bad.

 

[MH Hawker]

Re: '77 Merc 1500-Fix a faulty trigger?

In a word No you replace them.