OMC 165HP in-line six won't run with new coil???

[Clete_t]

I have a 1974 OMC electric shift with a 165HP in-line six. Engine has run well but while out trolling the other day engine stalled. A few minutes later I was able to start it, but then it died again about 15 min later and would not re-start. Got it home and put water hose to it and had neighbor "mechanic" come over. Engine started, after a while he noticed the resistor was extremely hot. Replaced resistor, but the resistor still got hot and noticed coil was getting hotter, but engine idled for over 30 min without dying.
"mechanic" recommended replacing the coil. Went to Napa with old coil in hand and they sold me a replacement. Put new coil in and engine starts and runs for about 15 seconds, dies and will not re-start. Put old coil in and engine starts and runs.

Question 1. How hot does a resistor get? Can it get too hot and what would cause this? 2. Why would a new coil not work? I'm not sure if NAPA will take it back. Could it be defective? 3. Any ideas on what the real problem is? Boat dieing after long periods of trolling at idle speed...

Any advice appreciated!

 

[kenny nunez]

One problem that happens to the in line engines is the rotor in the distributor gets so hot it starts conducting the spark to ground. The Mercruiser engines had that same problem and the repair is a new rotor that has the blade slightly longer so that the spark did not have to jump as far to the contact in the distributor cap. As far as the coil you bought I cannot answer that. The ceramic external resistor does get hot to the touch but should not smoke. With the engine running you should have 8-10 volts going to the + side of the coil.

 

[Clete_t]

Thanks for the reply Kenny. So today I started the engine with the old coil, no problem. I was so mesmerized by the new coil not working, that I went ahead and switched them back out. (p.s. i also did a lot of cleaning of the connections etc.,), so new coil starts right up, and never dies(let it run for about 15 min).. corroded wire? I dont know, but next step is I'll take it back out on the lake and see what happens (I now have my boatUs towing back in effect). But the resistor is still very hot to the touch (doesn't smoke, but very hot to touch. Also, I didn't see a positive or negative on the resistor, is there a certain way to connect the resistor? but I'll check the volts tommorrow.

By the way, my "mechanic" had a tachometer/dwell tester. I hooked it up and was running about 675rpm at idle and dwell was at approx 36 percent. I'll have to look into my manual, but does that sound about right?

As for a longer rotor, I would just take in the old one and have them find a "longer" one?

Thanks again for any input!

 

[kenny nunez]

If there is a Mercruiser dealer in your area they will have the rotor that you need. The resistor is not polarized and works either way it is connected. It would be a real improvement to change the points over to a Petronics kit. The engine will idle smoother and the distributor will operate a lot cooler. They are easy to install and will compensate a little for a worn distributor. If you keep the points try to get the dwell @ 40* .

 

[jerryjerry05]

The rotor blade: the blad? contacts the button in the cap or it wouldn't run right.
Just bend it back up.
IF?? the blade is bent and hasn't been making good contact and the spark is forced to jump.
Then the cap and it's button needs to be changed or the contacts cleaned.
​The carbon from the arcing could cause a problem. Get a new cap.

​The "new" coil: is it a resistor coil or no resistor?

The Resister should get hot.
It's taking 12v and breaking it down to 9v.


Measure the voltage on both sides of the resistor.
One side should be Battery voltage 12v and the other side 9v.
​Anything other than 9v and it's probably bad.
​12v can burn the coil up..
If memory serves right dwell is 29-31???