1957 Evinrude 35hp Compression 125 and 110

[tinkertinker]

I did this test cold, with the other spark plug removed and compression relief disabled... 110 psi and 125psi.

Is this right at the borderline of worrisome? From what I've read, these are decent #s, but a difference this size can be a bad sign.

The plug from the lower compression cylinder looks dark, wet, and dirty. The plug from the higher compression cylinder looks great.

I have a noticeable sheen following me in the water at idle, but have spark in both cylinders. Carb re-build scheduled next, then coils. I don't like this much oil in the water. When I disconnect the fuel line to burn what is left in the lines at the dock, the water discharge looks pretty awful, and white somethings are in the discharge.

[Bob_VT]

Those numbers are fine. Have you done a de-carb on the motor? I bet you will see the numbers get closer together after that. 10% is the key difference and those are w/in 10%

A sheen in the water at an idle is unburned fuel and common on older motors.

[R.Johnson]

On an engine this age, I would look at the cylinder walls. Those are good figure's, but I would not exspect perfect cylinders on an engine that age.

[tinkertinker]

Thanks for the quick answer on the #s. I was gonna give up if they were too out of whack.

The to do list is: Carb kit/clean (though I'm a little over my head), then decarb, then, if problems persist, new coils.

I should have also mentioned that this doesn't feel like 35hp... yet. It's on a very light 14ft Aerocraft.

Newbie Q: how does one look at the cylinder walls?

[Mas]

The only real way to look at the cylinder walls is to remove the head. I would not do this due to the risk of breaking head bolts....a bigger headache...pardon the pun. It sounds like a carb rebuild is in order as you mentioned...they can easily gum up...especially if they have sat. Also, what are the condition of your fuel lines....today's gas with ethanol breaks down the rubber causing havok in some cases.

Start easy! New fuel. Do a spark test to check the quality of the spark... hot and blue jumping over a 1/4 inch gap.

Mas

[tinkertinker]

I'm going to re-do the spark test. Neighbor had one with a little filament that lights up, but it doesn't tell me much about spark strength. I saw one with a gap for the spark to jump. will try. Thx!

[samo_ott]

Yes, use a gap spark tester, that's best.

[lindy46]

My '57 Lark throws a lot of crud in the water which is pretty noticeable at idle speeds (little milky popping bubbles in the water?). Pretty normal for the old motors. You may want to do a Seafoam decarb - may even out the compression some and clean out some of the crud in the cylinders. If it's running and idling farly good, coils are probably ok. If you have good spark, leave them alone, and just clean/rebuild the carb.

[JB]

This is the season for outboard hypochondria. It happens every year.

There is nothing wrong with your carbs or compression. A decarb might improve the already okay compression span.

If your impeller has not been replaced in the last 24 months it would be a good idea to change it.

Like many others, you are desperate for something to do to ensure a great boating season. Don't waste it fixing what ain't broke.

[tinkertinker]

Ha! thanks for cautionary note, JB.

This motor is new to me, so I have paranoia and hypochondria.