'57 7.5hp Evinrude, Sudden Bogging

[echo7]

Hey guys, always browsing these forums for tips and answers because you guys are awesome. Just can't seem to find something similar to my situation yet. Feel free to link another thread if you know of one.

So I've been using this awesome little motor for over a year straight now ('57 7.5hp Evinrude), every weekend almost. Last weekend, I go to take it out, get running full speed for maybe a minute, starts cutting out like it's starving (which is normal for mine here and there). Then, it starts bogging REALLY bad, but stays running smoothly. Almost seems like I fouled a plug but I don't know what running on one cylinder feels like so can't be for sure. I keep fiddling with the needles with no luck, full speed is barely over 5mph and a horrid bog. After a few minutes it dies, can barely get it started and running for more than 30 seconds, then can't get it started at all.

I take it the garage, do a full carb clean and check the plugs (J4C's). One won't spark for me so I find my spare ones (J6C's) and both of them spark on both wires. Put it all back together and on the boat, go to start it up, BAM, starts in 2 pulls, no bogging! I was amazed and figured I had it nailed. 20 seconds later, it starts bogging again! 15 seconds later it dies and I can't get it started. Grr!

I'm going to be picking up a new set of plugs to start, but just seems too quick to foul my spares. But I don't even remember how old they are anyways. Any other suggestions? Thanks in advance!

 

[jbjennings]

Re: '57 7.5hp Evinrude, Sudden Bogging

The problem sounds like a coil going out to me. Or, it could be a short in a plug wire or a crack in a coil wire letting the current go to ground. Either way, I think you have a problem with spark on one cylinder. Get a spark tester from autozone and see how much of a gap the spark will jump. Needs to be at least 1/4 inch.
Good luck,
JBJ

 

[F_R]

Re: '57 7.5hp Evinrude, Sudden Bogging

Remove the recoil starter and then the thin plate covering the flywheel. Look down in the hole and see what you see. Cracked coils??? Greasy points???

 

[Carusoswi]

Re: '57 7.5hp Evinrude, Sudden Bogging

Back in '92 I inherited my late father's '74 Evinrude 9.9 (my twin sister used it for four years following his passing in '87). The motor was fresh from winter storage and spring tune-up from the local dealer.

I started it up in a barrel to check it before taking it with me on a fishing trip to Canada. It seemed no one with me was familiar with this motor (I didn't even think it old at the time) as they kept telling me to mix 24:1 fuel for it, but I had the manual and insisted on 50:1.

On a boat, the motor ran fine for about five minutes, then, started to drop a cylinder. Back at the dock, the problem was quickly diagnosed to a fouled #1 plug. Replaced it, ran for five or ten minutes, same problem occurred.

All the old fishermen coots tried to tell me it was due to the wrong fuel mix, but I knew that could not be the problem.

Finally, I pulled the cover while out on the water and observed fuel sloshing around inside the lower housing - the obvious sign of some sort of fuel leak. The problem was then easily traced to a rotted portion of rubber fuel line under the cover (runs from the tank connector around to the carb I guess). The hose was long enough that I could just clip off that bad portion and slip the new hose edge over the spurred fuel line receptor (sorry, don't know the correct term for that part). After that, the motor ran like new for the balance of our 1-week fishing trip.

What I have never understood is why the leak caused that fouling on one plug only. That never made sense to me.

Not saying this is your problem, but it's something I would check for.

Caruso

 

[echo7]

Re: '57 7.5hp Evinrude, Sudden Bogging

Thanks for the ideas guys, the coil sounds like a good place to start. I've never even looked at it over the 10 years or more I've owned it. I'll post back when I get a chance to bring the motor back and have a look.

 

[jmendoza]

Re: '57 7.5hp Evinrude, Sudden Bogging

Caruso, the fuel leak was incidental and not in any way related to the plug fouling, you just happened to notice and fix a second unrelated problem while changing your spark plugs.

Now, what could have happened was the carb was not getting enough fuel due to the leak, and you richened up the low speed mixture, but then the line stopped leaking, the carb filled up, and then it became too rich due to the low speed being reset, and it fouled a plug. This would only apply if you reset the low speed mixture leaner after fixing the fuel line, and then the motor quit fouling plugs. Chances are however that the 25:1 mixture left enough extra depositis on your plugs (often not visible) to make the plugs foul, or they were old plugs. It also may be indicative of the point rubbing block wearing causing the spark to retard and be less intense, or a condensor going out(rare, but happens).
The early 1974 engines had a seven bolt thermostat cover which was revised for better circulation on later years, as the later heads have 8 bolt thermo covers. This was done to reduce low speed plug fouling. There is also a brown delrin ring that replaced the original one under the magneto plate that tightens it up and makes for smoother idling. Yours may also have the metal water pump cover if it's an early 1974.