Well after talking to a bloke who is adamant that they do work as log as they are installed correctly, I decided to give it a go.
I collected the following...
4 doughnut magnets out of microwave ovens. Look for late model high power ovens.
4 steel plates to sit at the back of each magnet and drilled to take zip ties.
4 spacers made of wood and slightly thinner than the diameter of the fuel line.
I assembled 2 sets of magnets with the South pole facing in and mounted them on the fuel line just in front of the air-filter at 90 degrees to each other as per the photos.
The result?
I have a "test track" which I use to compare vehicle performance. On the way home there is a railway crossing with a Stop sign. Then there is a 380m run to the top of the 9m high ridge where a 132kv power pole sits beside the road. For the last 37 years I have tested every vehicle that I have had, checking the speed on a GPS as I pass the power pole. Results varied between 75km/h and 132km/h.
When I was younger I owned some very fast vehicles but economy is now my main focus. Despite this I still like a responsive vehicle.
I own 8 Suzuki Carry vans that I have driven and the best time that I have been able to get was 95km/h when still relatively new and low mileage. Currently I have a 2004 Van with 240,000kms and is standard apart from a sports exhaust. Recently 90km/h was the best speed I could get until fitting the magnets. My first run after fitting the magnets was 97km/h. I have never been able to do that.
The van definitely is better to drive with more torque especially at 2000rpm and lower. The exhaust has a different, milder sound especially when the motor is under load.
I have been enjoying the extra go, so I can not report on fuel economy yet but I will be monitoring. When the van was newer, I could easily get 400km before looking for a servo. Recently that has been only 370kms, so I will note any improvement.