'93 25hp 2 stroke fuel/oil ratio

[Jason2tpa]

I purchased this engine recently. I have the original owners and service manual. The owners manual says use 100:1....the service manual says use 50:1 to "start" the engine. Which one should I be using and why? And let's say I'm suppose to be using 100:1...is there every a time when I should run 50:1, for a tank or two? Vice-versa

I have no idea how many hours are on the engine. I operate the engine in saltwater, warm conditions (Tampa, FL).

Thanks in advance!

[99yam40]

I believe they rethought the 100 to 1 and recommend 50 to 1 to make sure the internal shiny parts do not rust when set up for a few weeks in humid areas like around water

[boscoe99]

Nope, there has been no rethinking on Yamaha's part. It is still 100/1 for a number of two stroke models.

Messes with lots of folks minds. They equate more with being better.

The original break in oil mix was 50/1. After the break in, the ratio changes to 100/1. Some models specify 25/1 for the break in and then it changes to 100/1.

[rodbolt17]

ok
lets play beat the dead horse.

100/1 will work fine IF and ONLY IF you do your part.
your part includes routine scheduled maint of the fuel and cooling system following the hourly OR calender maintenance schedule.
at 100/1 there is NO margin for overtemp nor lean fuel mix.

now on to the LONG term storage.
Yamaha,and most others, consider ANYTHING over 30 days to be long term storage and now ya gotta winterize it.
by winterizing an outboard your not "protecting" it from freezing.
typically outboards are self draining.
what we are doing is protecting all them cool finely machined shiney parts inside and protecting the fuel system.

that's the rub that OMC switched from 100/1 back to 50/1.

at 100/1 there wasn't enough residual oil for "long term" storage.

cause nobody follows the long term,over 30 days, procedures.

you wont know ANY difference between 100/1 or 50/1.

none at all.

in the end either will work well.
its your choice.

[Jason2tpa]

Yes, that is what the manual states...50:1 break-in period then 100:1. Though other sources state you to continue using 50:1.

Appreciate all the good info guys. I'll keep 100:1 going.

[99yam40]

Just do not let it sit for long periods running it with that

[robert graham]

Why not just run it 50:1 and give yourself a bit more insurance against corrosion?....It can't hurt and it could save you a pitted bearing or crankshaft...

[boscoe99]

Why not run it 25/1 all the time and get more corrosion protection still.

Or, maybe 12.5/1. Even more corrosion protection.

[99yam40]

I still have some old Craftsman Chain saws that ran 16 to 1 that run well still.
I have no idea what I should be running in them except that is in the manual, so that is what I run