Magnets for fuel economy. A scam?

As gas prices are increasing, anyone of us is searching ways in order to save fuel.Most of us have seen advertisements in car magazines, newspapers and websites for "miraculous" magnets that promise fuel economy up to 30-40%, more power and less emissions. But, do these really work or are they just a scam? If they are a scam, why have companies been selling these "magnets" for years already?

According to vendors of these magnets, the story is as follows:

At the height of World War Two, the R.A.F. and the U.S.A.F. were trying to find ways of getting better range and performance out of their Spitfires and Mustangs, which were then running on poorer quality fuels. The Americans created a magnetic device which achieved this, but at this time it was decided that it was too heavy and cumbersome (the required field strength was only achievable by using electromagnetism back then). Today there is the ability to create even more powerful magnetic fields from devices no bigger than a small box.

The vendors of these magnets also say that when these magnets are placed round the fuel line, they can change the layout of hydrocarbon molecules in a fuel so that much more fuel can be ignited in our engine, instead of being emitted through the exhaust as partially burnt toxins and other by-products.

Someone would ask: Why automakers do not use magnets to make their cars more fuel efficient? 

We, at carbloggergr tried to find the answer by searching in hundreds of resources over the internet. We found in automotive forums, topics related to magnets and fuel economy.
We found two references from vendors of these products (forum 4tforum.gr) related to the effectiveness of the magnets concerning fuel economy.

Vendor 1:

Magnets are ideal for conventional engines with carburetors, but not so much for engines equipped with fuel injection.

Vendor 2:

The tests in the last 15 years, on new vehicles had no visible results. In my opinion, this is because the strong electromagnetic field in injectors, replaces the need for a similar product. As a result of this, the fit of the magnets in a car's engine has no effect.

The responses of both sellers indicate that magnets have no results in fuel economy. Although, there are reports from users in the forums where it has been observed fuel economy and in some cases performance improvement.

below, say these cases:

1. On older cars:

Model	Notes from the user
Mazda 323GT (2 διπλά καρμπυρατερ)	Up to 30% fuel economy, the engine works smoother
Peugeot 309 GTi	Up to 30% fuel economy, the engine works smoother
Zastava Yugo 45	Up to 20% fuel economy, the engine works smoother

2. On newer cars: 

Model	Notes from the user
Fiat Punto	Little improvement in fuel economy
Jeep Compass	Some improvement in fuel economy
Hyundai Accent	Much improvement in fuel economy
Opel Corsa D 2007 1.4	from 13.95 km/lt to 15.95 km/lt
Seat Ibiza	Little improvement in fuel economy
Skoda fabia I (101 hp)	Some improvement in fuel economy
Suzuki Jimny	From 7.6lt/100 km to 7.0lt/100 km

 Of course there were many reports from users of modern cars where there was no difference in fuel economy

Final notice

The use of magnets has effect concerning fuel economy in older non catalytic cars equiped with carburator. In newer cars generally there is no effect but there are some (very) few exceptions where fuel eonomy is observed.

Finally, if you think that it is worth to try the magnets in your car, you can get two strong ones for free from a damaged hard disc instead of buying them by using the instructions of the following video: