Fuel mix

[Knots]

My son has been inadvertently been using 50:1 fuel mix in my older Shindiawa 500 chainsaw. It is clearly marked 25:1 on the top cover. Has or will this damage the saw or is the quality of the new oil likely to cover the issue. He has run it for a few hours and says it is running fine. The saw is about 25 years old. Should I mix the Stihl synthetic oil at 25:1 for this particular saw?? I have been running a Shindiawa 360 for years at 50:1 with no issues.
Your thoughts would be appreciated.
Thanks,
Knots

 

[Wilhelm]

Old school 2-stroke engines used to run mineral engine oil in their fuel mix, hence the higher content of oil specified.

Running 25:1 on modern dedicated 2-stroke oil may actually foul up the engine/plug.

The saw should be fine, although I personally don't mix less than 40:1 even with modern 2-stroke oil.

 

[hacskaroly]

With all of the newer saws stating to use 50:1, there are some smaller newer saws that say to use 40:1. Like @Wilhelm stated, you should be good to go with the 50:1, but if it helps you feel better, go ahead and run 40:1, a little more oil should not be an issue. I run all of my stuff on 40:1, especially in saws that are over 50 years old.

One thing you can do every couple of hours of use is to pull the plug and the muffler and take a look. See if the plug has the right color and if the piston is nice and shiny (no vertical racing stripes).

 

[Wilhelm]

The consumer should keep in mind that the 50:1 is greatly , if not solely, a result of restrictions and pollution regulations.

 

[Coupe]

I use 40:1 in all my later model saws except for a couple of
the real old ones I drop it a bit down to 30:1.

 

[aljewett]

My buddy owns a small engine shop. He said that 50:1 was more of an EPA thing. If you run 40:1, it's a little better for the engine, but he hasn't noticed a real difference. I went to 40:1 in all of my 2 strokes, some are newer, some are older, like my 1974 LawnBoy. New mix oil is much better than the old SAE30 that used to be used. But, if you want the best stuff, buy pre-mixed. It will last 2 years on the shelf.