what is the difference betwwe a 40:1 & 50:1 mixture??

It doesn't. Popular misconception. A 40:1 mix oil should only be mixed at 40:1 and a 50:1 mix oil (such as Stihl oil) should only be diluted at 50:1. Never ever get and oil which states a recommended dilution ratio on the bottle and dilute it at any other ratio. You will either under oil your mix or over oil your mix. Either way your machine will start and run, but too rich and you will foul the plug, block the exhaust and cause excessive smoke. Too lean and you run the risk of scoring or seizing your engine resulting in a huge bill at the best or a write off at the worst.

As a rule of thumb the better quality the oil the less oil you need to have correct mix protection. Always ready what thew manufacturer of the oil says is the correct dilution ratio of their oil- not what the manufacturer of your machine states as the two ratios will or could conflict with one another.

pleasant
December 2008