Two-Stroke Engine Fuel Ratios

atios. What is it in the design of a two-stroke engine that requires a cert ain ratio? Is it the compression ratio? I googled around but couldn't find a good explanation on why the weed whip needs 50-1 and the chain saw needs

It must have to do with design tolerance or materials used...unless you hav e an old 2-cycle where the oil additives were not as good as today. If you only have those 2 mixes...go with the 40:1 on both.

that use different gas/oil ratios. What is it in the design of a two-stroke engine that requires a certain ratio? Is it the compression ratio? I googled around but couldn't find a good explanation on why the weed whip needs 50-1 and the chain saw needs 40-1.

When I took a small engine course years ago, I asked the same question. The teacher said the engines are not at all fussy. As for me, I run 32:1 in everything. Figure I'd rather run rich than lean. Lawnboy likes to use the special non smoking oil or some such thing. I've not tried a Lawnboy engine for anything, not sure it's needed there either.

I suspect the difference in ratio is based on the machining and manufacturing -- hard versus soft steel for example.

IDK either, but I think there is a trend over time, no? That new engines use less oil? Are there still new engines that use 32:1?, etc. Less would be better to reduce emissions. And the new oils are better, synthetic, so less can be used.

I've heard some of the new synthetic oils run

My two cycle Lawnboys were finicky about using oil other than theirs so that is all I used.

I'd use their stuff and ratio in chain saw and week wacker without problem.

The saw is likely older, and works harder. The "older" relates to the oils available at the time of manufacture. I'd likely use 50:1 oil mixed at 45:1 for both as a matter of expediency.

Don't use oil designed for 40:1 at 50:1

Several of the 100:1 synthetics have been "recalled/relabelled: with cautions not to use beyond 50:1, apparently.

I've seen some of these oils that say they are good for ALL 2cycle engines. Just add contents of the bottle to a gallon of gas (or 2 gallons, or whatever is marked on the bottle).

I've never used that stuff, buy wanted to mention it. I rarely use any

However, I always believed in adding a little more oil, rather than less. It might smoke a little, but at least it's well lubricated. If the OP only has a 40 to 1 and a 50 to one. I'd just use the 40 to 1 in both.

Echo says the mix oil used in their 2 cycle engines has to meet JASO FD, ISO-L-EGD specs or the warranty is void. Their (pretty expensive) brand of oil does-- but so do some generics and other less expensive brands.

Don't recall what I was using but shop told me that it was reason I was having problems that I brought to them. I did not want to inventory different mixes so used the same in all. I had two Lawnboys, neither of which would start one spring so I traded them both in for a 4 cycle Honda.

Echo also states in their manual:

Echo premium Power Blend X TM Universal 2-Stroke Oil may be mixed at

Small engine shop I use said that if I use the pre-mixed fuel (no alcohol) I can use the 50:1 mix across the board and all will be well.