Calling all ignition experts - bad trigger? ('85 60hp Merc)

[Joe_the_boatman]

Short story long, bought this motor and never had it run right.

Symptoms:
It starts fine, idles fine, and idles in gear fine. It will run WOT for between 30 sec and 5 min, then quit and be hard to start. After it starts, it will limp home idling, but give it any more throttle and it will die again.

I FINALLY got an out-of-spec reading on something today. On the trigger, wht/black to brown, white, or purple is open, where it should read 800-1400 ohms (I just double checked as I typed this). DVA is 14V for each (at 1K RPM). DVA for brn, wht, prpl to ground is 2.7V, 2V, and 2.5V @ 1K RPM, which falls into spec.

My question is, with an open reading like that, should it be running at all?






Additional specs, if you're not convinced it's the trigger:

Compression:
100/110/110 psi

Fuel:
After a hard run and it quitting, spraying premix directly into the carbs when trying to start or while running doesn't increase revs - it floods it and it dies. I've rebuilt both carbs with new parts, adjusted float height, and rebuilt the fuel pump. I've run a fuel line straight from the tank to the fuel pump (to bypass all fittings) and that didn't help either.

Ignition:
Did a link-n-sync last fall and set the timing per spec. Replaced rectifier (new RadioShack version). New CDI stator. New NGK plugs.

Specs:
CDI Stator (warm engine): High side: 2880 ohms, Low side: 57 ohms;
DVA @ 1K RPM: Blue to GND: 210V, Red to GND: 130
DVA @ 2K RPM: Blue to GND: 270V, Red to GND: 240V

Switch box to coils (DVA): 160V/160V/160V @ 1K RPM

Charging voltage:
16.2VDC @ 1K RPM
16.5VDC @ 2K RPM
16.5VDC @ 3.5K RPM

Coils:
Tested primary/secondary and they were within spec. Didn't record the #'s though last fall.

 

[sledstew]

Re: Calling all ignition experts - bad trigger? ('85 60hp Merc)

I would trust the voltage verses the ohms, humidity and other things can affect ohm readings.
Just a suggestion--

Have you done a leak down test on it by chance? My theory which Ive had happen was that the water jacket was cracked and once the block heated up enough it would allow water into the cylinders and basically drown it out. Then it would cool down and contract to where it would run again aftr cranking and getting the water out of the cylinders. The whole time the compression read above 110 on every cylinder..

 

[Joe_the_boatman]

Re: Calling all ignition experts - bad trigger? ('85 60hp Merc)

Thanks Sled - that agrees with what I've read doing my research, that water may be entering the cylinders. I'm trying to find out how to do a leak down test now. I have an air compressor, and can rig up gauges. I'm guessing that the cylinder in test would be at 1/2 way to TDC, with the flywheel held stationary. Would 1/2 way down be far enough to not interfere with the exhaust port?

I've replaced plugs after the engine's died on the water, but didn't notice water coming out of the cylinders (didn't turn the motor over either, though). The engine ran like crap once the Autolite plugs were replaced with NGK's (while I was out on the water). Engine runs (idles) fine now in the driveway with NGK's. This is why I thought I had an ignition issue.

 

[Joe_the_boatman]

Re: Calling all ignition experts - bad trigger? ('85 60hp Merc)

I'm going to pick a leak down tester on the way home today (I use any excuse I can to buy more tools).

Until then, I have another question. There are 2 rectangular exhaust ports in the rear under the engine cover. These spit water out along with the exhaust. Is that normal?

 

[j_martin]

Re: Calling all ignition experts - bad trigger? ('85 60hp Merc)

Spent cooling water is sprayed into the exhaust. It's normal.

On the meter readings on the trigger.

A very small gap in the wire will show as an open with an ohmmeter. When current flows, it might temporarily "heal" to allow it to run. Intermittents like that are hard to find.

If you're sure of your probing for resistance, I'd replace the trigger and expect to see it fixed.

The worst problem like that I ever saw was a diode on a relay in an IBM mainframe type printer. It sent electronics all over the room to eternity over a 3 week period and drove 4 engineers nuts. I did a formal matrix analysis on the 3 weeks of work and found the part was the only commonality in the system. A 50 cent radio shack diode fixed the problem. The diode would short out, blow electronics next time the relay was actuated and open up. In that circuit an open diode wouldn't show as a fault. On some subsequent closing, it would short again. Then open............ad infinitum.

hope it helps
John

 

[sledstew]

Re: Calling all ignition experts - bad trigger? ('85 60hp Merc)

Leak down test has to be done so the piston is far enough toward head that the compressed air cannot escpae through the intake or exhaust ports

hope this helps

 

[sledstew]

Re: Calling all ignition experts - bad trigger? ('85 60hp Merc)

Ive also seen those motors work fine until they are submerged in the water which created mnore backpressure on the motor causing more of a leak.

 

[Joe_the_boatman]

Re: Calling all ignition experts - bad trigger? ('85 60hp Merc)

Ive also seen those motors work fine until they are submerged in the water which created mnore backpressure on the motor causing more of a leak.

I (only) run mine in a water-filled bucket to simulate being on the lake - the back pressure does make a big difference. I can even put it in gear in the driveway that way, which is how I did the link-n-sync and adjusted the idle (while in gear).

I have yet to do the leak-down test - I had a late day at work yesterday. I will do it tonight or tomorrow.

I found a new-looking 85hp Suzuki for $1500. It'd be nice to be out on the lake instead of wrenching in the driveway on the weekends. I'll give the ole' Merc another shot I guess.

 

[Joe_the_boatman]

Re: Calling all ignition experts - bad trigger? ('85 60hp Merc)

Just as an update, in case this thread helps anyone out, I finally got the trigger off today and there was a break in one of the wires at the trigger.

It's been replaced by a brand new CDI unit, and I also replaced the switchbox with a CDI unit I got (used) for $50. I have yet to lake test it, but will post the results when I do.

The wht/blk wire was broke, which is switched to the other 3 wires as the crank rotates. It shouldn't have run at all with that wire gone, but somehow, it did.