Fuel/Oil ratios... Why the variations?

[CN Spots]

I know the proper answer is to just do what the manufacturer says but I've seen mixtures on vintage outboards that were 30/1 and some that were 35/1... is there really that much difference in those ratios to justify an additional fuel can in my shop? I've taken in several motors over the past few years and it seems that all of them have a different fuel/oil ratio. Some are severe, some are minor. I was just wondering if those guys got it right back then or were they just playing it safe and over-oiling. Adding a vintage kicker motor next to a modern 110 would be a lot easier if one could just switch the fuel line between the two and not have to carry two tanks. Now I'm not talking about running 50/1 in a 25/1 eggbeater, that's a pretty far stretch but if they're only off by 5-10/1, would that guarantee catastrophic failure or would it probably be ok?

 

[BuzzStPoint]

Re: Fuel/Oil ratios... Why the variations?

I dont know the correct answer.

But I would think if you have a couple of outboards, 30/ & 35/1 I dont think the 5 ratio would make that big of difference. I would rather run richer then lean on oil.

 

[Silvertip]

Re: Fuel/Oil ratios... Why the variations?

The engine manufacturer designed and built the engine using materials (specifically bearings) with the oil technology available at the time. In the 1930's, 1940,s and even into the 50's regular 30 weight engine was used. These engines smoked like crazy because auto engine oil was not designed to be consumed in the combustion chamber. As two stroke oils (regular and synthetic) came available the ratios were changed. By the 60's nearly everything was 50:1. Some small outboards had bushing style bearings rather than the ball and roller bearings as in modern engines. Those bushings needed lots of lub whereas the ball and rollers live nicely with much less lub. Two stroke oils were also designed to be consumed during combustion and they also produced far less carbon build up.

 

[CN Spots]

Re: Fuel/Oil ratios... Why the variations?

The engine manufacturer designed and built the engine using materials (specifically bearings) with the oil technology available at the time. In the 1930's, 1940,s and even into the 50's regular 30 weight engine was used. These engines smoked like crazy because auto engine oil was not designed to be consumed in the combustion chamber. As two stroke oils (regular and synthetic) came available the ratios were changed. By the 60's nearly everything was 50:1. Some small outboards had bushing style bearings rather than the ball and roller bearings as in modern engines. Those bushings needed lots of lub whereas the ball and rollers live nicely with much less lub. Two stroke oils were also designed to be consumed during combustion and they also produced far less carbon build up.

Interesting. I never took into consideration the evolution of the oil. So do you think it's possible to run an older motor say for example a 35/1 (w/roller bearings) on a modern 50/1 ratio using modern 2 stroke oil?

 

[F_R]

Re: Fuel/Oil ratios... Why the variations?

Ask 50 people and you will get 50 answers (opinions). Some with a shred of validity and some pure bunk.

 

[sethjon]

Re: Fuel/Oil ratios... Why the variations?

Don't think there is a real correct answer but go with the 30:1 for everything. A little more oil won't hurt.

 

[Brewman61]

Re: Fuel/Oil ratios... Why the variations?

Ask 50 people and you will get 50 answers (opinions). Some with a shred of validity and some pure bunk.

You'll be lucky if all you get is 50 answers.

I had a snowmobile from 1974- back in the day it was considered fast. Dangerous but fast. Had two ignition systems- 2 spark plugs in each cylinder.
Had to mix at 20:1. One quart oil to 5 gallons gas. That was a smoker.

 

[JB]

Re: Fuel/Oil ratios... Why the variations?

I've only been messing with outboards for around 60 years. I guess I am still a newby. What make and models are manufacturer specified for 30:1, 35:1??

 

[Silvertip]

Re: Fuel/Oil ratios... Why the variations?

Bearing lubrication is only part of the lubrication requirements in a two stroke. Piston skirts and cylinder walls need to be lubricated as well. Again -- metalurgy and oil technology of the time also dictated what the mix ratio should be. Even porting of the engine can have a bearing on fuel mix because it affects how quickly the mix gets into and out of the engine. The only way you will know if it's safe to use 50:1 in a 35:1 engine is to try it. If if doesn't work, the repair is on your nickle.

 

[CN Spots]

Re: Fuel/Oil ratios... Why the variations?

I've only been messing with outboards for around 60 years. I guess I am still a newby. What make and models are manufacturer specified for 30:1, 35:1??

You're correct. Mind left me. 16/1 and 24/1 to be precise on the really old motors. Still close enough for me to question though.

And yes, I'll probably still run them as suggested. Just curious as to their reasoning for the ration variances.

Thanks.

 

[Boss Hawg]

Re: Fuel/Oil ratios... Why the variations?

Don't think there is a real correct answer but go with the 30:1 for everything. A little more oil won't hurt.

I agree EXCEPT for plug fouling on say a engine that "requires" a 50;1 mix

 

[cougar1985]

Re: Fuel/Oil ratios... Why the variations?

I've only been messing with outboards for around 60 years. I guess I am still a newby. What make and models are manufacturer specified for 30:1, 35:1??

yes you are a newbie!wont let you work on my 70 year old outboard!lol.

 

[coolguy147]

Re: Fuel/Oil ratios... Why the variations?

even if the motor has modern type bearings it still was not made to scavange a 50:1 of oil and gas. it was made to scavange 24:1 and leave it to that.