For most people using magnets, even for manufactures of such products, it's a hit and miss situation due to lack of testing, quality control and understanding. It is all about energy charge and one should put magnets not only on the fuel line but also on the air intake. I've seen fuel magnets on fuel lines only to find out the polarity is wrong or was not carefully understood during the assembly process - for that it is a hit and miss situation. When you look on existing patents, a lot are also done not the right way but they are patented. Whatever the reason behind, one thing for sure they do not work well. Any magnet can help when implemented right.
This is important and should be done accordingly. First the magnet to use should have one side only south and the other side only north like those circular flat magnets. Bar magnets with one side having two poles does not work. For the fuel line, the south side of the magnet must face the rubber hose. For the air intake rubber/plastic tube, the north side must face the rubber/plastic. Never put on metal parts like aluminum or stainless intake tubes. If one could put 6 magnets all north facing the air intake tube in hexagonal formation, the better.
If you have this strong fuel magnet product which consist of two clamping magnets on the fuel line, remove them and check the poles using a compass, only place one magnet on the fuel line, south pole facing to the fuel hose and the other magnet on the air intake, north pole facing the tube. This will work on all combustion engines regardless of fuel. If you stock weaker magnets together to add more strength, it can also add improvement but there is a limit on the number you can stock on top that it no longer add more change. On my setup, 5 pcs of small 1/2 inch diameter x 1/4" thickness circular magnets is the limit. I have three stocks in line, making them 15 pcs on the fuel line. The stocking limit could be different on your vehicle and type of magnet. I only use ordinary ceramic magnets similar to that in small speakers. I've done this on diesel engines, gasoline engines and motorcycles, all work well when done right - meaning engine performance instantly improved with the magnets.