Oil to Gas Mixture Ratio

[BIGJOHNG2 1]

I would like to get your consensus  on the best oil to gas ratio to use on O & R engines. On the operating instructions I read , thoroughly mix 3/4 pint of outboard oil  or any good # 30 SAE oil  and 1 gallon of regular gasoline. The decal on the motor says mix 1/3 pint SAE 30 Heavy duty oil (MS type or equal) with 1 gal 70-80 octane gasoline.This gives a ratio of about 24 : 1. There is a bit of a difference between 3/4 pint and1/3 pint to 1 gallon gasoline  What about gas ...I would guess ethyl alcohol free fuel would be best on the seals etc. However, on a modern 2 stroke weed eater that I have had for years I do use regular gas, BUT always run the machine dry after each use. Has anyone used a mixture of 32:1 and ran their machines for some time without any trouble? Your opinions ...

Thanks,

John

[Wallfish 698]

Always better to err towards more oil.

With that being said and modern oil much better than that old stuff was, I run  mine on 32:1 with a quality oil.

Non ethanol is always better but they'll run fine on the corny crap too.

[CNew 404]

Like Wallfish suggested, I’ve had great luck with the Toro 32 oz fuel cans and mixing with Stihl oil. BUT, I’ve never run any of my O&R engines for extended periods - I use this mix to get them running and then on occasions for short spurts just for fun.
 

https://www.toro.com/en/homeowner/walk-behind-mowers/fluids-4-cycle-canned-fuel-131-3823

 

[ranger 373]

One thing to consider, altering the fuel/oil mix for a two stroke, especially one with a fixed jet, ie, motorcycle, is, increasing the oil content reduces the fuel amount, resulting in a potentially damaging ‘Lean’ running condition, if subjected to high rpm and load for extended periods.

Doug.

[BIGJOHNG2 1]

Interesting Dough. Never thought about the oil mixture... that by increasing the oil would lean the fuel burn. Would the opposite then be true? Like using 32:1 make the engine run richer? How then does the mixture screw on the carb enter into the picture?

Thanks,

John

[ranger 373]

20 hours ago, BIGJOHNG2 said:

Interesting Dough. Never thought about the oil mixture... that by increasing the oil would lean the fuel burn. Would the opposite then be true? Like using 32:1 make the engine run richer? How then does the mixture screw on the carb enter into the picture?

Thanks,

John

If you have a ‘High Speed’ mixture adjusting screw on your carb, the later ‘Walbro’ carbs did not, you can adjust the mixture at max speed to suit, (see relevant manual). This is similar to (re-jetting) a fixed jet carb, to compensate for fitting a different air filter or free flow exhaust system to your car, for example. A lean mixture can result in overheating and burnt/melted pistons. Insufficient oil content can result in seizures, especially when throttle closed after a high speed/high load run. (Shutting off oil supply). This happened not infrequently with 2stroke racing motorcycles which had a fuel/oil mix lubrication system. It’s probably safer to stick with the manufacture’s recommendations regarding ratios. Consider car engine oil, modern engine components are machined to much tighter tolerances than years ago. Use an oil formulated for an older engine type, (Usually a high viscosity), in a newer engine with hydraulic tappets etc and you will almost certainly destroy it in a short time. The same the other way round, (a modern ‘thin’ oil) in an older engine, which requires a higher viscosity due to greater machining clearances. Whether synthetic 2stroke oil is really suitable for older engines, who knows? Not to mention the different types of additives in oils, (or lack thereof) nowadays!

Doug.