Mercury - Quickleen Engine and Fuel System Cleaner Fuel Care System Liquid Cleaner Formula 8M0047931. Overview. You can usually feel it before you can explain it. The engine doesn't sound quite as smooth. Throttle response feels a little lazy. Maybe there's a hint of knocking when you lean into it, or the idle just isn't as steady as it used to be. That's the stuff that can steal confidence on the water, especially when you're far from the ramp and you just want your motor to run clean and stron