Is 100:1 gas/oil ratio safe for my 2-stroke Yamaha?

[puffcard]

I use 75:1, but we run close to wide open. If you run at lower RPMs go with 50:1.

[a64pilot]

Originally Posted by fxykty

Correct, that is backwards. I’m looking at p.26 of the Tohatsu M6-9.8B 2017 manual and it shows during break-in 25:1 and after break-in 50:1.

We were having trouble with plug fouling trouble recently and the service guy suggested we use 100:1. That seems like not a lot so perhaps 75:1?

I’d try going up a heat range or two on the plug before I leaned out the oil mix

[Compass790]

Originally Posted by puffcard

I use 75:1, but we run close to wide open. If you run at lower RPMs go with 50:1.

I'd do it the other way around. An oil injection pump on a 2 stroke increase the oil ratio as the throttle is opened. I believe I read somewhere they are at almost 200/1 at idle

[JimsCAL]

My 1999 Yamaha 2hp manual said 50:1 breakin and then 100:1.

[Lake-Effect]

Originally Posted by Compass790

I'd do it the other way around. An oil injection pump on a 2 stroke increase the oil ratio as the throttle is opened. I believe I read somewhere they are at almost 200/1 at idle

We have a scooter that does that. But scooter engines are used differently than outboards. Scooters idle often, and have more acceleration cycles.

Running at idle isn't under load, so less oil would be required. And outboards seldom idle for long periods (or shouldn't, anyway). Running under load at less than high rpms is arguably more stressful to the engine, and there's less oil and gas flowing into the engine, so a higher oil ratio makes sense.

A 50:1 ratio seems to work well for us, and we seldom run our outboard at more than 50% throttle, or for long periods.

[David M]

I would experiment with running the oil mixture a little richer in an effort to prevent scoring and increase engine longevity. If it fouls the plugs then obviously back off.

[a64pilot]

If it fouls the plugs, then the plug heat range is too cool.
Why do I say that? Because there are many, many engines running 50 to 1 and don’t foul plugs that’s why.

There isn’t any difference in design between a 50 to 1 engine and a 100 to 1 engine, nothing that would cause excess carbon build up or fouled plugs etc if you run it at 50 to 1.

There isn’t any difference in an oil injected engine either, that’s why so many were successfully run on pre-mix forever, although I’ll agree oil injection when it works probably does do a better job of lubricating an engine.

[model 10]

When I messed around with dirt bikes I never thought of changing the fuel ratio, just the spark plug heat range.
Ah, the smell of castor bean oil. WW1 pilots with rotary engines got the trots from all the castor oil they ate.

[a64pilot]

Originally Posted by Ecos

When I messed around with dirt bikes I never thought of changing the fuel ratio, just the spark plug heat range.
Ah, the smell of castor bean oil. WW1 pilots with rotary engines got the trots from all the castor oil they ate.

Yes but they were getting it in their face, it was the reason for the scarves across their face etc., and of course the extreme cold.

I've seen a rotary motor in the Museum at Mesa Arizona, actually a brilliant design when you look at it, the valve springs were tiny and weak, just good enough for starting, the rocker arms had weights on them, the faster the motor spun, due to centrifugal force, the stronger the "spring" became, thereby freeing up power normally wasted compressing springs, and of course it was just the right amount, never too much or not enough.

I have my Wife's Grandfather's A&P books from the 20's, he got his license via mail,
there is a page that opens up and shows the parts of the average airplane, it a Curtiss JN-4 Jenny

as smart as we think we are know, its amazing what they knew then, the difference is back then they explained why you did this or didn't do that, now they just tell you what to do or not do and don't explain.

And this was early 1900's, a whole Century ago

[Bruce K]

My first Seagull O/B ran 10 to 1, we always used used sump oil, and carried 3 or 4 spark plugs for a days outing!

[evm1024]

Originally Posted by a64pilot

SNIP

as smart as we think we are know, its amazing what they knew then, the difference is back then they explained why you did this or didn't do that, now they just tell you what to do or not do and don't explain.

And this was early 1900's, a whole Century ago

Working at a university I come across some who think we are so much smarter now.

Sometime I agree with them and say " So true, we are so much smarter than Aristotle, Plato, and Socrates".

[bobnlesley]

Originally Posted by wingssail

...Less oil also means less smoke, which is also an emissions issue, of course...

We have a 3.3hp Mercury 2-stroke bought in the UK in 2001 which is labelled 1:100 mixture ration, we also have the exact same motor albeit a Nissan bought in the Caribbean in 2017 which states 1:50; having spotted the anomaly, I queried it on a yachting forum and got a lovely answer from an outboard mechanic:
Originally these engines (they're all re-badged Tohatsu) had a recommended mix of 50:1 but by 2001 the EU were getting ansty about 2-stroke outboard emissions so Mercury and the rest made a significant design change to these motors to comply; at great expense and effort they had some new decals saying 100:1 and stuck those on instead. Now that 2-strokes are banned in the EU and many other places, they've reverted to the original 50:1 badges in countries where they can still be sold new.

[model 10]

[QUOTE=a64pilot;2908066]Yes but they were getting it in their face, it was the reason for the scarves across their face etc., and of course the extreme cold.

There is a special knot for scarves. Any other knot you try will end up with you getting slapped to death in no time by an end.

[Don C L]

I always had a lust for the RD350 and then later the RD400.. never got to ride one though...
now who's heard of Jawa?

[ggray]

Originally Posted by Don C L

I always had a lust for the RD350 and then later the RD400.. never got to ride one though...
now who's heard of Jawa?

I remember Jawa.

Never owned a motorcycle, but lusted for one when I was a teenager.

I'm thinking there was something unusual about Jawa, such as no brakes, or single gear transmission. Something. Am I close?