I asume we are talking about gasoline, not fuel. Deisel has a different set of problems (biological growth) and the solutions are differnt too.
The most common problems with gasoline is water, particularly if using e-10. I posted some links:
Sail Delmarva: Ethanol and Gasoline and Diesel - References
Other than holding a sample up (for the bottom is best), there is one other simple test. Take your sample and cool it way down (freezer); you will see if the gasoline contains disolved water that may be causing trouble (this sample should NOT be pulled from the bottom, because yuo don't want the free water). Water tends to fall out of e-10 when the temperature drops, because while it will hold a good amount of water in warm temperatures, it will not in cold temperatures. This is one of the reasons we get a lot of problems in the fall.
Review the chart on page 2.
If there is wate in the gas, suspect a leaking gas cap first.
Other than that, the gas should be clear and free of dirt. Octane should not be an issue for an Atomic 4. Loss of volitiles can also be an issue if the gas is quite old (more than a few months) and this is not simple to test for. Some engines are more sensitive than others.
As always, many "bad gas" problems are actually carb problems. Boat carbs seem to need cleaning every 2-5 years, because of the sporatic use. Get a manual--it's not hard.
Gas additives are a waste of time and money (I am in a related business and have tested most). Replace the gas if it isn't the carb. And don't pump it out with a drill-pump (I saw the aftermath).