Sounds scammy to me, but for $20 bucks is it worth cutting your fuel line? 
Get a tune up instead.

----------
> From: matt <msanner@hooked.net>
> To: Multiple recipients of list <vanagon@lenti.med.umn.edu>
> Subject: Increase in performance??
> Date: Wednesday, December 11, 1996 1:09 AM
> 
> Hello:
> In my pursuit to increase gas mileage I came across this item . It is a
> device that fits over the fuel line that reduces emissions and increases
gas
> mileage. Is this a hoax or a scam???
> 
> goto:
> http://www.edmunds.com/edweb/JCWhitney/Parts/81ZC0523.html
> 
> Matt
> ----------------------------------------------------------------------
> >...computers in the future may have only 1,000 vacuum tubes and weigh
> >only 1/2 tons."      --  Popular Mechanics, March 1949