Like someone said - post your model number if you can so we can be sure what the mixture should be.<br /><br />As far as what the ratio means - 50:1 means 50 parts gas to 1 part oil. This comes out to be approximately 6 gallons gas to 1 pint of oil. Generally, if you buy TCW3 oil (which is the kind designed for two cycle outboard engines), the various mixture ratios will be printed on the container as well as how much oil to add to how much gas for a particular ratio and particular amount of gas.<br /><br />Definitely dispose of the old fuel. If it's been sitting a while, you might need some work to get it started - but for starters, get fresh fuel and oil mixture. You should also change the lube in the lower unit. Then try to start it - in the water and see how it runs. You might be fine - or you might have to rebuild the carb (pretty easy even for me, a non-mechanic) and replace the water pump impeller (another pretty easy DIY). Good luck , have fun.
