I use a small outboard motor on my sail boat. I had problems 2 years ago. Tried B12 and it cured it. I have started treating every tank with success. Was talking to an outboard mechanic asking what he thought. He said he has seen motors that have some age. Using a fuel treatment the fuel line inside small pieces flaking off and stopping up the carb. He said reatments do clean the varnish but also eat fuel lines. He mentioned another brand of additive when making that statement. I follow the directions to the letter. Most years don't use a tankful (3gal) the whole season. I transfer to something else . So far I have been happy with B12 and have convinced other boaters to use it. It's almost a must for engines that are used in small amounts. Sorry about previous post, my comments were not showing up as I typed. Thanks