Intermittent Ignition issue

Or I believe it's ignition.

Evinrude 70773S 1977 70 HP

Coming back a cross the lake last weekend just cruising at about 3K the motor suddenly falls off. I mean suddenly boom RPMS drop to 2K and the tone of the engine changes. Full throttle only nets 2900 ish RPM when it was getting me 4200ish. Ran it like that for a bit and then as suddenly as it fell off full power came back. This, to me, says I lost a cylinder. Motor did this a couple more times, with a varying duration, on the 20 minute trip back.

On the muffs last night motor ran fine. Have spark on all 3 cylinders as check with a timing light. Went through the ohm testing of the trigger and stator is presented in the Clymer and all is ok. Coils all ohm out the same but that may mean little as the resistance is very low at 2 ohms.

Problem does not seem to be heat related as the motor was stone cold before starting out and we had been out cruising for much longer earlier in the day with no issues.

Any clues? Is there voltage checks I can do? I can't seem to find tests for this year motor.

Re: Intermittent Ignition issue

When it acts up, pull one plug wire at a time with an insulated pliers to find out which cyl is acting up.

Re: Intermittent Ignition issue

boobie said:

When it acts up, pull one plug wire at a time with an insulated pliers to find out which cyl is acting up.

Click to expand...

yes that is the plan but the way this boat is configured it's easier said than done. I was trying to see if there was any testing I could do out of the water on the muffs due to access being much better.

Re: Intermittent Ignition issue

Put it on the muffs and rev it up to about 1500 rpm max. Then try it.

Re: Intermittent Ignition issue

had it out again today and the issues keep shifting. No problem with a cylinder cuttng out but the motor won't idle worth a darn. Got it set for 900 in forward gear, which is high, but now it's back to the old issue of stalling out, especially when shifting between gears. I don't think the spark is as strong as it should be but I was able to pull a plug wire on all 3 and determine they are all firing. Gunna make a DVA so I can troubleshoot some more but this is really frustrating.

Re: Intermittent Ignition issue

Bought the parts to make a DVA and tested the ignition today. I feel like the DVA is not working correctly as I'm only getting 5V from the timer base lead to ground and the troubleshooting info I have says that should be 150+. Also I'm getting the same reading into the coils and that also should be 150+. While testing the timer base voltage I accidentally touched the test probe and got lit up pretty good so it seems like there is more then 5 volts there. If I test the DVA on a battery it functions as it should in that it reads full voltage then slowly drops after the leads are disconnected which is adding to my confusion.

Any advise? Is 5 volts enough to fire the coils?

Part of the trouble shooting procedure says if the voltage reading from the timer pack is low disconnect the trigger wires and retest. I'm working by myself and so I set the meter on "hold" and cranked the motor from the key. The meter read 0 volts so it appears there was no voltage from the timer base but I have no idea what that means. The guide tells me what it means if the voltage goes normal but not if it goes away. All the other voltage testing I'm doing with the motor running so I can see what the meter is reading in real time.

Another test is to check voltage between the timer base wire and the "sensor" wires which should be at least .5V. I read 1.5 so that is good but the resistance reading should be between 10 and 20 ohms and mine reads 8 on all three leads. Does that mean the timer base is faulty. On Friday I'll have another 70 I'm getting from a friend that was running fine until it threw a rod so I may just start replacing parts. I'd really like to know if I'm chasing ghosts though.

Re: Intermittent Ignition issue

So I determined that my DVA adapter was built wrong. Miss read the instructions and bought the wrong size capacitor. It's working now and everything tests out ok according to the procedures on CDI's website. It was getting dark so this was a good time to check the quality of the spark. With the motor running I pulled a plug wire one by one with the pliers grounded. Spark was able to run out of the boot and arc to the pliers. This is a long jump and it was white hot so apparently I have no spark issue right now. Still no clue why I'm having the current idle problems. Need to check timing next.

Re: Intermittent Ignition issue

after more troubleshooting I've found this is a fuel issue. Starting a new thread.