The ratio values are, e.g.
40/1 = 40 parts gas to 1 part oil
50/1 = 50 parts gas to 1 part oil
so, you can see what happens when you add more gas to either....
your best bet is to mix a fresh batch at 40:1 and use it in all 2 cycle engines.
hth

Cuerno: For the limited use you intend if the 50-1 Ratio Mix is Premium Air Cooled Oil than no problem . If your worried throw in an additional Ounce of Oil . I have ran 50-1 and higher on my Old Weed-Eaters for Yrs without any issues. Carbon build up from to much Oil is far more of a Engine Killer than a slightly leaner mixture , especially with today's Higher Quality Oils .

I just used a tank full of 50/1 mix in the Feather lite FL20 without any issues so I will use up the rest of the gallon of 50/1 and next time mix some 40/1 when this runs out. Thanks alot guys for your info, and if you get a chance to get yours hand on a zeroturn mower its like heaven sent.

Cuerno: Not so far off in the future for this Old Dog lol ! The Push Mower Routine is getting a little much with the acreage I have currently .

NO!!! YOU DON'T ADD MORE GAS TO THE 50:1 RATIO TO GET 40:1!!! The more gas you add to 50:1, you get like 60:1 or 80:1. That would be a sure way to kill the engine.

If you use good oil, just put the 50:1 you have on the other trimmer and it should be ok. Don't add any gas into the 50:1!!!!