Gas/Oil Ratio

Storm56 · Jul 4, 2012

It is the concentration of the OIL that determines a mix ratio, NOT the piece of equipment. Look at what the OIL is rated for. In the past common oil ratios available were 16:1, 25:1 and 40:1. Today 50:1 is the most common. You can run ANY piece of 2 cycle equipment safely at a 50:1 ratio regardless of what the manufacturer stated in the original literature as long as the OIL is rated at 50:1.

I use non ethanol 89 octane fuel mixed at 50:1 with a 50:1 oil for ALL my 2 cycle equipment including my fathers old craftsman chainsaw from the 70's. So check what the OIL is rated for and mix accordingly. The main killer of 2 cycle equipment is a mis-adjusted and/or dirty carburetor. Learn how to properly tune your 2 cycle equipment, use good gas mixed according to the OIL spec and you will never burn up an engine.

Fossil Farm · Jul 4, 2012

I have used Opti-2 (used to be Optimol) for many years. It is a synthetic 2 cycle oil. Has worked well for me for all my weedwackers, chainsaws and tillers so far. Not sure if it is the best solution to having a different mix for each different engine, but so far so good.

Bluegill2 · Jul 4, 2012

Storm56 said:
It is the concentration of the OIL that determines a mix ratio, NOT the piece of equipment. Look at what the OIL is rated for. In the past common oil ratios available were 16:1, 25:1 and 40:1. Today 50:1 is the most common. You can run ANY piece of 2 cycle equipment safely at a 50:1 ratio regardless of what the manufacturer stated in the original literature as long as the OIL is rated at 50:1.

I use non ethanol 89 octane fuel mixed at 50:1 with a 50:1 oil for ALL my 2 cycle equipment including my fathers old craftsman chainsaw from the 70's. So check what the OIL is rated for and mix accordingly. The main killer of 2 cycle equipment is a mis-adjusted and/or dirty carburetor. Learn how to properly tune your 2 cycle equipment, use good gas mixed according to the OIL spec and you will never burn up an engine.

Bingo, when I started running saws in the late 70s', it was 32:1. I still have one of those old saws and now run it 40:1, like I do all mine, old and new. I run mostly Stihl Ultra full synthetic. And non ethanol 91 octane.

newbury · Jul 4, 2012

#1. Run non-ethanol gas if at all possible.

#2. Running greater than 40:1 (i.e. 25:1) can cause problems and is not needed with most modern oils. From another forum:

However, oil affects the richness indirectly but in an opposite sense.
If your mix has more oil and less gas (eg 25:1) then if the same amount of mix enters the chamber as a 50:1 mix, then the 25:1 mix produces a leaner gas air ratio.
Some of the oil components do not burn but scavenge soot and smoke (ie unburnt oil and gas) this robs the mix of gas and effectively leans the gas-air ratio.
The difference is small but it may be enough to cook a saw if someone switches from a saw tuned for 50:1 to 25:1 without retuning.

So be sure to tune your saw for the mix.

Don't leave mix in the saw- it eats the fuel lines, especially if you've violated #1.

LD1 · Jul 4, 2012

I guess I have always wondered why I hear soo many complaints about spark arrester screens plugged. I guess now I know....if people are still mixing 16:1 and 25:1 on modern stuff with the mentality of "what can more oil possibly hurt" :confused2:

joshuabardwell · Jul 4, 2012

Storm56 said:
It is the concentration of the OIL that determines a mix ratio, NOT the piece of equipment. Look at what the OIL is rated for.

Thank you! That is what I always thought and the comments so far on this thread were starting to make me wonder.

I do wonder, however. I have some 2-stroke oil, the kind where you squeeze the oil into a top reservoir to measure it out, and the top reservoir has markings for multiple different ratios. I was a bit surprised to see that, since I would figure the oil would only be pre-marked for the ratio it is designed for. Maybe it's designed for 50:1, and they put the other markings on there in case people want to intentionally use a lower ratio for some reason?

Storm56 · Jul 4, 2012

I of course have seen what you are referring to. I have 2 thoughts, one is that many people still believe in the "my saw manual states" rule and manufacturers do not want to lose sales. And two is that if Johnny homeowner has an old saw which is not in proper tune and/or repair, uses the new oil at 50:1 and toasts the engine, who do you think he is going to blame? It gives the manufacturer an "out" and provides them with a defense.

newbury · Jul 4, 2012

If I'm milling I prefer to run my 660's at 40:1. Milling puts more stress on the saw because they are at WOT for up to 10 minutes. Just felling or bucking I'll run them and my other saws at 50:1.

But remember to tune them for the mix.

MikeInMaine · Jul 4, 2012

Good topic, and lots of answers I agree with. I noticed in the manual for my Jonsereds it says not to use synthetic 2-cycle oil. My point is you can learn stuff if you read the manual.