Oil/fuel mixture conversion

[Seagull1975]

I have a 1974 Silver Century plus Seagull outboard motor. It says in the manual the oil/fuel mixture is 10:1. But I have been doing some research and I have found out that these motors can be converted to 25:1 fuel oil mixture. Just wondering what is involved in doing this? Does the motor need any different parts installed?

[Keith.P]

Just a matter of replacing the main jet, from a 45 to size 40 jet.

[Seagull1975]

Are those main jets difficult to find?

[Charles uk]

First check which fuel ratio it is jetted for, it might have already been converted!

[Seagull1975]

Is there a way of me knowing what jet is in my carb?

[Keith.P]

You will have to take the back jet out and have a look at the number, accessed from the bottom, after removing the large nut at the base of the carb.

[Oyster 49]

Just be careful removing the carb bolt as it screws into aluminium and the threads can be weak due to corrosion. Don't overtighten. They usually run well on 25:1.

The reason for the different jet, is that is you reduce the amount of oil in the fuel the mixture will be richer and thus the engine will be running rich.

[Seagull1975]

I would never want to do something to shorten the life of the little motor or hurt it in any way. But.. If it is fine running on 25:1 I would love the advantage of less smoke.

[headdownarseup]

Use a modern semi synthetic (and sometimes bio-degradable) 2 stroke oil if its less smoke you're after.

Jon

[Oyster 49]

Outboards tend to run cooler than other engines, so use an oil designed for outboards. TCW3 I think is the spec, you can get biodegradable to that spec too, which actually makes your seagull quite green too.

A quick search of the forum found this thread.

viewtopic.php?t=4028