1985 70hp evinrude dies at cruise after warming up

Hi E1, longtime reader, first time poster. Recently my 1985 70 Evinrude died on my way in. Acted like I ran her dry and she seized. Fired up after a momentary cooling and started to cruise again. Shut off after several minutes again, again refireing after brief cool down. refired and limped in.Fuel bulb firm, fuel still visible in filter. Next day I pull plugs and do a compression check and all is well, 110,+- a few lbs on each cylinder. Next I go thru the fuel lines, replacing 1 old cracked original hose. Ran better, still shut off at cruise, after warming, within 1 mile. Limp in. This time I replace the original power pack, coils, and plug wires. Go for a test,motor never ran smoother, same results. Now I check the stator, resistance is 1.5, book says 1.3+- 0.1, but that looks good enuff. Check rectifier, diodes are all working. So to summarize, originally happened after a day of fishing, now shuts off after 1 mile, every time. Gone thru fuel lines,new primer bulb, new power pack and coils, stator and rectifier test within specs. Don"t know what to do next, any suggestions would be much appreciated, Mark

Re: 1985 70hp evinrude dies at cruise after warming up

You don't mention any warning horn sounding off! If overheating (seizing), the horn should be blaring constant and steady long before the engine siezes up.

The warning horn should sound (Beep) momentarily when you turn the key to the ON position... does it?

To test the horn, (engine not running), have the key in the ON position, then find the TAN wire protruding out of the cylinder head... ground out that wire. The horn should sound off steadily when you ground that TAN wire. Does it?

Does the fuel primer bulb have a tendency to go flat? If so, you have a fuel restriction which is usually the anti siphon valve at the built in tank.

Let us know what you find.

Re: 1985 70hp evinrude dies at cruise after warming up

correct, no buzzer sounded, i just added a update about the fuel line. Fuel tank is 18 gal. under my console. I'll check my water temp sensor, see if it sounds. be right back

Re: 1985 70hp evinrude dies at cruise after warming up

buzzer works, just checked by grounding the tan wire, fuel bulb remains firm, and has each shutdown. One of the test I did was to run with a timing light hooked to #1 plug wire, and it quit firing at same time motor shutdown,

Re: 1985 70hp evinrude dies at cruise after warming up

Intermittent or temperature dependent ignition failures are nasty. Your timing light test was a good idea. You say your engine completley dies, it doesn't just bog, so we can assume the other two cylinders quit sparking as well.
You measured the resistance of the battery charging winding (yellow wires 1.5 Ohms), but the power pack is supplied from the brown and brown/yellow wires which should have a resistance about 450 Ohms. But with intermittent issues resistance measurements are not very meaningful, there might be an isolation failure in that winding or a tiny crack in the winding which shows up at temperature only. To identify this you need a DVA adapter (peak voltage reading adapter) and a voltmeter. Disconnect the yellow/black kill switch wire from the power pack and measure the peak voltage on this wire (power pack side) to ground. It should be about 300V. With the kill switch wire disconnected the engine cannot be shut off with the key switch anymore, use the choke instead or short the two cables into the DVA adapter (mind the 300V).
Another possibility is that the rectifier shorts one of the diodes at temperature. It's easy to check, just disconnect the two yellow wires, the engine can be run that way.

Re: 1985 70hp evinrude dies at cruise after warming up

I'll try running with the rectifier, (2 yellows) unhooked, that is the easier of the 2. I'll have to find a DVA adapter. thanks alot for the help

Re: 1985 70hp evinrude dies at cruise after warming up

if it acts like its siezing and requires cool down before it will turn over again, you need to check the water pump regardless of the buzzer sounding or not when it occurs or when you jump it to test.....

long story short i have been down this road with my 95 70hp, same symptoms that you describe, not checking and replacing a $50 waterpump kit has cost me about $2800

details here http://forums.iboats.com/showthread.php?t=407852

turns out the guy that rebuilt it for me to the tune of $1300 didnt replace my impeller inspite of telling me he did and 1 yr later the same issue occurred, so i went rebuilt powerhead and checked the waterpump for myself and discovered a scored up housing and impeller that was VERY hard and dated 1995..... it was intact and pumping what i thought was a decent tell tale stream, however now with a new impeller and housing its MUCH MUCH stronger and cold all the time

Re: 1985 70hp evinrude dies at cruise after warming up

Thanks, checked more wiring for shorts, found nothing today. New impeller this season, broke my lower unit shaft so went all thru the new(used) lower unit I found. I went ahead and ordered a new stator and rectifier, changed everything else, might as well do them to. All original stuff, had the boat since 1990, so not to bad. I will keep you posted, I'll change them one at a time, see which one it is. I would imagine it is the stator.

Re: 1985 70hp evinrude dies at cruise after warming up

UPDATE, well, bad news all around. Started to get worse, running that is, turns out to be a rod bearing #2 cyl., ooops. Oh well, got some good electrical parts if i find a replacement motor. Thanks foe the help anyway.