1957 Evinrude Big Twin. A couple of questions.

[shinola]

So I ran across a nice Big Twin, model 25028, and comparing to the smaller ones of the same year, I have found some differences that I'd like to learn more about.

1. What is the purpose of the Cut out switch and how does it operate?
2. What is the purpose of the mercury switch and is it possible or adviseable to eliminate it for simplicity?
3. The compression relief chambers are interesting. Are they only for pull start? I see how the lever operates them when using the rope start. Are the chambers opened when using electric start? My motor is not electric start, but I'm searching for parts to convert it. I'm not sure my back can handle cranking the 35 for many more years.

In general, are there any other unique items to know about?

Thanks.

 

[fdrgator]

1 & 2. If the motor is revved up a bit in neutral, it will want to run away and be hard or difficult to slow it down. The vacuum cut-out switch senses such a runaway condition and shuts down the spark on the lower cylinder till it slows down. The mercury switch works in conjunction with the cut-out switch to ensure it works only during a runaway condition. Don't be defeating stuff that was put there for a purpose.

3. The compression reliefs only when pulling the starter cord. They are closed at all other times, including electric starting.

 

[racerone]

Your location.----If in Canada----evinrudeparts.ca----Might be able to help with electric start parts.

 

[shinola]

Thanks Gator, I won't mess with it, just didn't understand the purpose.

Racer, thanks I'll keep that in mind. Local swap meets coming up here in FL through AOMCI will be my first option.

Another observation I had. The by pass covers on this one appear to be ready for a fuel pump, even though this is a 1957 and set up with a two line pressure system. Is it just a drill through the center of one of the covers to modify and make it ready for fuel pump? Would it be best to locate it on top or bottom cylinder?

Is 433941 The proper powerhead gasket kit for a 1957. It comes up in online searches, but I haven't found a place to confirm.

 

[fdrgator]

If the bypass has the 3-hole pattern, a fuel pump will mount directly to it. Only one hole, yes drill and tap for a hose fitting. It really doesn't matter, top or lower cyl.

433941 is totally wrong, not even close. But sorry, I don't have the correct number.