Yes I'm a noob and thank you so much in advance for your forgiveness of my lack of experience. I have tons of experience with automotive and exactly 0 with outboards. But I'm looking forward to the challenge. I've been spending waaaaayyyy too much time lurking over all the threads I could find here over the last several days. I am so grateful that you guys are here and I hope I can get a lot of help and provide some along the way as well.
I recently inherited a 1977 Starfire Tri Hull with a 1977 Johnson 75. Not knowing how long it had been sitting, I pulled the carbs and cleaned them up. I also cleaned out everything from the tank to the carbs. I replaced the plugs. It fired right up. I let it run for about 60 seconds while on muffs. It seemed to idle ok.
A couple of days later I did a compression test just to know. Compression was good at about 135 with no more than 5 deviation. Now comes the problem.
Thinking that everything was done with the motor, I began cleaning the boat out and getting it ready for a test run on the water. I hosed it out and cleaned a nasty oil mix spill where the gas tank sat. After the cleaning I went to start the motor again. Nada. Dead. It would crank just fine but not even think about firing. It now has no spark. With assistance from the search function on this board I did a couple of tests. First I removed the blk/yel kill wire from the power pack. Still no spark. I inspected all the wires that I could see. I found the insulation rotted on the red wire on the rectifier. I cleaned it as best I could, removed the old rotten insulation and recovered it with new shrink. I tested it with my ohm meter and it seemed fine. I removed both yellow wires from the rectifier and tried it again. Still nothing. I also put an ohm meter on the stator wires and got 640 which sounds like it is within specs. I'm already thinking power pack but want to diagnose it as thoroughly as possible before spending over a hundred bucks for a new one. I read in another post that I should ground all 3 coil wires before doing the compression test. I didn't do that and have never done that on any other gas engine so that sounds weird.
On a seperate note, after it sat for a couple of days I went out and found about 1/4 cup of thick black oil that had leaked out from around the prop. I read in the FAQ section here that oil leaking from there is usually settled mixing oil and of no concern, but to me it just seems too black and thick like actual crankcase oil. We can attack that after I get the motor running again though.
You may want to consider getting a service manual, the fault tracing procedure for your ignition is in there in detail. I have the '75 70 HP and the red lead on the rectifier was frayed badly, so replacement was all I needed.
Leaking oil is just unburnt oil/gas from the exhaust which exits through the prop/hub, once you get going, do a de-carb. Run a full can of SeaFoam mixed with 3/4 gallon gas through it, that will clean it up for sure.
The manual is here...and you guys are sure right. The detail it goes into in a step by step manner to troubleshoot is great. Now I just need to find a DVA. Has anyone here built the one that was drawn up by Bill Rogers in this forum? Does it work?
I never did end up buying a DVA. I probably should own one but will wait until I can justify the $100. I just used my DMM to do as many tests as I could (ie. ohms tests and some voltage). I tried measuring voltage at the stator and trigger coils with the DMM. I was able to see about 1 volt on each of the 3 trigger sensors. That was a good sign. I then tested for voltage at the stator and got some screwy voltage readings that were not consistent. I assumed that is where the DVA is required. That fact that I was getting some activity as opposed to nothing at all told me that it "probably" wasn't the stator. Next I measured for any voltage output from the power pack. Absolutely nothing. I had no measurable voltage of any kind exiting the power pack to the coils. I decided to gamble and just replace the power pack. It fired right up and seems to run great. So, the power pack was the bad guy in this case.