older OMC (79) engine won't start

[taxijim]

I have an older OMC 350 ci GM engine that until this season ran OK. This season every time I put it in the water it would run but only at low throttle. After much internal debate and trying other options I decided it was the rochester quadrajet carb and so got another one. Anyway yesterday I took it out with new carb installed and it still ran the same! Got up the lake aways and decided to take a look at the points, etc.. in the distributor cap. It has not run since. The batteries ran down and even after trying to jump it off another boat it wouldn't start and I had to get towed back to shore and now when I check the coil here at home there is no spark. I had another coil from a previous similar engine and installed it but it still has no spark. The coil says on it "use external resistor" what does that mean and where is it in my boat?

 

[Bondo]

Re: older OMC (79) engine won't start

Got up the lake aways and decided to take a look at the points, etc.. in the distributor cap. It has not run since.

Ayuh,... My guess is, the Problem is in the distributer, probably the points...

 

[taxijim]

Re: older OMC (79) engine won't start

Thanks ......makes sense I will go out and change the points out now. 1 thing that concerned me tho,is that in the process of attempting to "jump" the battery, 1 of my "deck hands" inadvertently hooked up the live cables to 1 of my batteries backwards creating quite a spark and I don't remember if the ignition was "on" at the time or not, if it were on could that have blown something else ?

 

[kstrick08]

Re: older OMC (79) engine won't start

I am in the process of figuring out my ignition system on my 1967 Mercury 95 hp outboard. From what i have read in my repair manual, if you hook the wires up the wrong way on the battery the Switchbox will get fry'd. Not sure if you have a switchbox since you have points, but thought id share.

Good luck with your engine. i wish i could be more helpful

 

[Blk-n-Blu]

Re: older OMC (79) engine won't start

Your deckhand may have blown one of the 50 amp fuses. Usually in a large fuse holder at the rear of the motor. Just a thought!

 

[taxijim]

Re: older OMC (79) engine won't start

Just went out and changed the points, and had a friends brother come over with some test equipment to discover I have a bad coil wire! I thought I had tested it and it was OK! Anyway, now off to the local marine shop to get a new set of wires (the plug wires don't fit very tightly on the distributor cap, either) . Will update if this fixes it - thanks everyone who responded so far.

 

[taxijim]

Re: older OMC (79) engine won't start

NOT THE COIL WIRE! But dohave another coil on order as I am still getting no spark from the coil. The leads going into the coilare both getting 12V readings with the key "on" but nothing coming from the coil when engine is cranked.... BTW the battery that was shorted out yesterday while trying to jump, now doesn't register or put out any voltage when the switcher is set to "both" batteries, so my switcher may have actually taken a deep fry then - thanks for the heads up!

 

[Bondo]

Re: older OMC (79) engine won't start

The leads going into the coilare both getting 12V readings with the key "on" but nothing coming from the coil when engine is cranked....

Ayuh,... Are you sure you got the new points in Right,..??
The (-) post on the coil is supposed to be Grounded by the points....

 

[taxijim]

Re: older OMC (79) engine won't start

I just went out and double checked, and there nis 12v (actually 11.36) coming from both posts with the key on. I have even tried switching the wires around just in case they may have become discombobulated during switching out of coils, etc.... I need tomention, however that the coil switched was used, with status unknown, as I an still awaiting te new one I have ordered. To be sure I even have switched back to the original coil and am getting the same readings. Is this indicative of a bad coil? I even tried hooking up both sets of leads to the "bat" side of the coil and the other post still reads 12v

 

[taxijim]

Re: older OMC (79) engine won't start

should read there IS 12v - instead of nis - sorry for the typo

 

[Howard Sterndrive]

Re: older OMC (79) engine won't start

coming from both posts

not very descriptive

volts don't come or go

voltage is a measure of potential (electrical pressure) between two places in a circuit.
If you had the black voltmeter lead on one post, and the red lead on the opposite post you should read:

0V with the points open

8 to 10V with the points closed

 

[Howard Sterndrive]

Re: older OMC (79) engine won't start

If you put your red lead on the + post of the coil, and black lead on good ground or batt negative, you should read 8V to 10V anytime the key is ON
and 12V when the key is in the cranking position



The full 12V should only be measured in the cranking position, as your 79 OMC uses a resistance wire to drop the voltage to the coil
supplying a continuous 12V potential to the coil will burn it out


The wire to your + coil terminal should be purple/black- that is the reduced voltage supply
then, there should be another wire running around to the starter solenoid 'S' terminal to give full 12V during cranking for a hotter spark during cranking

 

[taxijim]

Re: older OMC (79) engine won't start

Thank You! What I meant by getting the 12v (actually 11.35) reading was with the key on and the red lead to the voltmeter on either post with the black being on a good ground. Perhaps my resistance wire is defective seeing that my voltage with the key on is so high. I need to ad, however that reading is with both 12v batteries engaged via the battery switcher switch, i will go out again and try it with just 1 battery turned on. BTW, was wondering whereabouts that resistance wire is located, and if the voltage reading is appropiate for both posts of the coil when using the black lead to a ground.

 

[Howard Sterndrive]

Re: older OMC (79) engine won't start

The purple/black wire is usually a resistance wire. Or a '79 might have an actual ballast resistor like the 73 setup pictured here:
http://hhscott.com/evinrude/images/wiring/73_OMC_V8_all_big.jpg

 

[Bt Doctur]

Re: older OMC (79) engine won't start

Before you go throwing more money at it, try resetting the points . If the points never close ,you will never get a spark.

 

[taxijim]

Re: older OMC (79) engine won't start

THANK YOU 1 AND ALL! It sems that the yahoo with the test equipment yesterday that informed me that I had a bad coil wire put my new set of points in and gapped them about 5 times too wide, thus making it impossible for the points to EVER close and as was so wisely advised to me in the last post, their will be no spark until they can close. I also put a new condenser in, but it was resetting the gap that just had my baby fire right up for me in the driveway (with earmuffs and water on of course) Thanks again everyone and you may see me again real soon if my acceleration problems are still present once I get her back in the water (if it ever stops raining!)

 

[cr2k]

Re: older OMC (79) engine won't start

One thing to also check is the advance. pull the dist cap and see if you can turn the rotor. If not at all or barely you will need to pull the breaker plate and clean and lube the advance weights and lobes. If it flops back and forth you need to replace the springs. Rusted advance weights will limit your full advance and full power. A good advance set up will turn smooth and about 15 degrees clockwise.

On a points ignition engine that has been sitting the first thing to suspect is corroded points.

 

[taxijim]

Re: older OMC (79) engine won't start

I am really glad I stumbled upon this boat forum, and the help has been immensely helpful! When I had the dist. cap off earlier, I did turn the rotor approx. 15 degrees and it seemed to turn OK - fairly smoothly, however it that may have not always been the case in that I did spray a small amount of multi-purpose lube into it the distributor right at the spring/weight set the other day after I had begun trying to diagnose the no spark problem which may have helped to lube them up some, in any case, the proof is in the pudding so to speak and I will be crossing my fingers at trying to get it up to full power again on my next outing. Thanks again everyone! - TaxiJim