1974 Evinrude 9.9-one cylinder stops firing at slow speed

[Carusoswi]

This motor belonged to my father, probably had 150 hours on it when he stopped using it in 1977. I've probably put another 20 hours on it over the years. Had it serviced when it came to me back in 1993.

. . . this motor always ran fine. This season, it has started to 'loose spark' in one cylinder at slow speeds after running for 15 minutes or so.

Last weekend at the lake, it ran like a champ at all afternoon. I figured my tweeking the rich/lean dial did the trick.

Then, when we were finished having our fun and were on our way back in, I had to slow down to pass some fishermen, and the one cylinder thing started happening again. Anything less than half speed, one cylinder. Open her up, and, after a couple of coughs from the non-firing cylinder, she kicks in and the motor runs fine at wide open throttle.

Slow down to half throttle, and you lose that cylinder.

What should I be looking for in order to diagnose/fix this problem.

Thanks.

Caruso

 

[mikesea]

Re: 1974 Evinrude 9.9-one cylinder stops firing at slow speed

Is it possible you leaned it out a bit too much?Did you try adjusting during the problem>assuming its not that.Im wondering if you may have a cut plug wire ,or something grounding out.I believe your eng has the points and condender ignition.They are maint items which,if you havent ever,should actually change,also,the older ,under flywheel coild have a tendancy to shed its insulation over time.Its not a use issue,its and age thing .Take your flywheel off,using a harmonic balancer puller ,or flywheel puller ,many auto stores lend or rent,but,if your keeping the eng.Id buy one.You should be able to get one for about $20 with bolts.You will see your flywheel has 3 holes tapped for that reason.Im thinking as your mag plate under the flywheel rotates,you could be grounding out due to a cut plug wire ,Or ??something.Usually ,a cyl will drop out undr more power not less ,that is why Im thinking that.Let us know what you find

 

[Carusoswi]

Re: 1974 Evinrude 9.9-one cylinder stops firing at slow speed

Thanks for the reply, Mikesea. I started it up on the boat this morning (impeller submerged in a large garbage can of water), and while it was running on one cylinder, tried pulling the spark plug wire to determine which cylinder it was (it's the bottom one).

I pulled a plug out of my Johnson (Bombadier) 25 HP and replaced that plug, and she began running just fine. I also turned that front idle adjustment screw carefully to it's inmost limit, then backed it off a turn and a half (as I have read in one of the threads here that that is where it should be set), then adjusted from there.

Took her out on the lake an ran her all day with not one instance of that cylinder dropping out.

Mind you, this problem has been occurring over the last couple of seasons, and I had previously swapped out both plugs for those that run fine in my 25 hp without success. I have also tried brand new plugs.

The motor was an absolute pleasure to operate today - ran like new. But it bothers me that it sort of fixed itself and I still don't know what was the cause. I have a hard time accepting that there was anything wrong with the plug I removed. I'll be using it in my 25 next time I take that motor out.

Will go out and get what I need to investigate further.

BTW, we've had this motor in the family since my dad bought it new. It was always well maintained (he would have it stored/serviced over the winter at his local Evinrude dealer). The outside case (plastic part) shows the wear and tear from years of fishing, but underneath that motor looks brand new.

. . . a fun motor to use when it runs like it did yesterday.



Thanks for the suggestions.

Caruso

 

[Carusoswi]

Re: 1974 Evinrude 9.9-one cylinder stops firing at slow speed

Is it possible you leaned it out a bit too much?Did you try adjusting during the problem>assuming its not that.Im wondering if you may have a cut plug wire ,or something grounding out.I believe your eng has the points and condender ignition.They are maint items which,if you havent ever,should actually change,also,the older ,under flywheel coild have a tendancy to shed its insulation over time.Its not a use issue,its and age thing .Take your flywheel off,using a harmonic balancer puller ,or flywheel puller ,many auto stores lend or rent,but,if your keeping the eng.Id buy one.You should be able to get one for about $20 with bolts.You will see your flywheel has 3 holes tapped for that reason.Im thinking as your mag plate under the flywheel rotates,you could be grounding out due to a cut plug wire ,Or ??something.Usually ,a cyl will drop out undr more power not less ,that is why Im thinking that.Let us know what you find

Took the motor out last Sunday. Only time it sputtered was when I let the first of two fuel tanks I carry run out (guess I can't complain about that).

It makes no sense to me that swapping a plug should fix the problem (I know that first plug wasn't bad), but, if it is now running perfectly, I'm thinking I should not mess with it.

Perhaps just running it has fixed something. . . who knows.

Thanks again for your suggestions.

Caruso

 

[jmendoza]

Re: 1974 Evinrude 9.9-one cylinder stops firing at slow speed

Caruso, you are over thinking this one, you had a fouled plug, plain and simple, even if it looks good, toss it. Plugs are too cheap to re-use. On my 9.9 I have had great luck using B7-HS plugs. Bottom cylinder will always foul first if you are too rich on the low speed as it runs cooler.

You should check the timing, as points do wear and when they do the gap changes which can reduce the spark intensity, and timing.

 

[bktheking]

Re: 1974 Evinrude 9.9-one cylinder stops firing at slow speed

Question is why is it fouled? Sounds to me like the ignition system isn't up to spec, putting a new plug in just masked the problem. While it will work for a while i'm thinking it may come back. Your motor is a points motor, have you checked the health of all the components under the flywheel?

 

[Carusoswi]

Re: 1974 Evinrude 9.9-one cylinder stops firing at slow speed

Caruso, you are over thinking this one, you had a fouled plug, plain and simple, even if it looks good, toss it. Plugs are too cheap to re-use. On my 9.9 I have had great luck using B7-HS plugs. Bottom cylinder will always foul first if you are too rich on the low speed as it runs cooler.

You should check the timing, as points do wear and when they do the gap changes which can reduce the spark intensity, and timing.

LOL, I am an over thinker. That's why I'm up at 4:30 AM on the computer reading through this forum (rather than being out on the water - now is the perfect time).

I will probably always over-think this motor, as it has great sentimental value - being my dad's, being genuine OMC, etc.

Caruso

 

[Carusoswi]

Re: 1974 Evinrude 9.9-one cylinder stops firing at slow speed

Question is why is it fouled? Sounds to me like the ignition system isn't up to spec, putting a new plug in just masked the problem. While it will work for a while i'm thinking it may come back. Your motor is a points motor, have you checked the health of all the components under the flywheel?

You're right, I need to check things out.
Caruso