with reference to fig1 an engine 10 has an intake 11 which is fit with one embodiment of a carburetor arrangement 12 . a flow of a hot vaporized fuel 13 and stoichiometric air 14 is regulated as a mixture 17 through an intake throttle regulator 15 and throttle body 16 . the throttle regulator 15 is illustrated in a partially - throttled orientation . the stoichiometric fuel / air mixture 17 to the engine intake 11 is a result of the action of the novel carburetor arrangement 12 which comprises a main combustion air gallery 20 connected to the engine intake 11 ; a heat exchanger or vaporizer 21 ; and a fuel / air regulator 22 ( best seen in fig3 and 4 connected through a flange to the vaporizer . the fuel / air regulator is a conventional low - capacity carburetor for precise control and metering of a rich mixture of fuel 24 a and a carrier air 24 b as a rich mixture 25 through a fuel passage 26 into the vaporizer 21 . the amounts of carrier air 24 b admitted through the fuel / air regulator 22 are less than a stoichiometric amount normally required for operation of the engine 10 , relying instead upon on commingling with a majority of main combustion air 14 being admitted through the main air gallery 20 . commingled air from the main air gallery 14 v and the carrier air supply 24 b stoichiometric amounts of air for the operation of the engine 10 . the carrier air 24 b from the fuel / air regulator 22 is sufficient to carry the rich fuel mixture 25 through the fuel passage 26 . the engine intake 11 is provided with a 300 - micron stainless steel screen 30 as a precautionary measure for arresting and flame or flareback . with reference to fig1 and 2 , the vaporizer 21 is a heat exchanger that enables transfer of heat from hot engine exhaust gases 31 to the cooler rich fuel mixture 25 . one embodiment of the vaporizer 21 comprises an annular fuel chamber 32 fit about the main air gallery 20 ( see also fig6 a ). another embodiment finds the vaporizer 21 located adjacent yet separate from the main air gallery 20 ( see fig6 b ). the fuel chamber 32 has an inlet flange 23 for connection to the fuel / air regulator 22 for forming the rich fuel mixture 25 which flows into the fuel chamber 32 . the fuel chamber 32 also has an exit 33 , preferably annular , into the main air gallery 20 . within the fuel chamber 32 , and also preferably formed about the main air gallery 20 , is formed an independent hot exhaust chamber 34 for giving up heat to the fuel chamber 32 , yet remaining sealed therefrom . the exhaust chamber 34 is provided with a plurality of parallel fuel tubes 35 passing independently therethrough and spaced circumferentially about the gallery 20 . hot exhaust gas 31 enters the exhaust chamber 34 at a tangential exhaust inlet 36 and circulates about the fuel tubes 35 , exiting at a tangential and opposing exhaust exit 37 for return to the engine 10 . the orientation of the exhaust inlet and exit 36 , 37 can vary , however with the objective to maximize contact of hot exhaust gas 31 and the surface area provided by the fuel tubes 35 . the fuel tubes 35 are open to the fuel chamber 32 at a feed head 38 to admit the cool rich fuel mixture 25 and are open at a discharge head 39 to collect a hot rich fuel mixture 13 from each tube 35 . as illustrated in both fig1 and 2 , the flow of rich fuel mixture 25 is preferably directed in through the fuel passage 26 to the fuel chamber 32 , around and down an outside annulus between the fuel and exhaust chambers 32 , 24 to the bottom of the fuel chamber 32 for distribution to each of the fuel tubes 35 . the rich fuel mixture 25 is then directed up the fuel tubes 35 for receiving conductive heat from the hot exhaust gases 31 . the discharge head 39 collects and directs the vaporized fuel 13 through the annular exit into the main air gallery 20 . this particular arrangement , having the hot rich fuel mixture 13 exiting adjacent the top of the vaporizer 21 aids in minimizing the height of main air gallery 20 and the carburetor arrangement 12 overall . a main air sleeve 40 projects substantially concentrically into the main air gallery 20 . as the sleeve 40 is smaller in diameter than the main air gallery , the fuel chamber &# 39 ; s annular exit 33 is formed for admitting hot vaporized fuel mixture 13 from the fuel chamber 21 and into the gallery 20 . the flow of the majority of the air 14 through the sleeve 40 and into main air gallery 20 forms an low pressure at the annular exit 33 , inducing and drawing the vaporized and hot rich fuel mixture 13 into the main air gallery . other means for forming a draft or suction are possible as illustrated with a venturi arrangement shown in fig7 c . as shown in fig3 - 5 , a hot exhaust pipe 50 from the engine 10 is connected to the exhaust chamber 34 . means such as a “ y ” junction 51 and diverter gate 52 ( fig5 ) control the flow of hot exhaust gases 31 . the diverter gate 52 is operable between a heating position ( down in fig5 ) where at least a portion of the hot exhaust 31 is diverted to the vaporizer 21 , and a bypassing position ( up ) where most exhaust gas 31 bypasses the vaporizer 31 . in the heating position , hot exhaust gas 31 circulates through the exhaust chamber 34 and around the tubes 35 for heating and vaporizing any rich fuel mixture 25 passing therethrough . preferably , a substantially co - current heat exchange between hot exhaust gas 31 is formed through a flow of cool rich fuel mixture 25 up the inside of the tubes 35 and hot exhaust gas 31 up the outside of the tubes 35 . with reference to fig3 and 4 , the vaporizer 21 is adapted for connection to one or more exhaust manifolds 53 of the engine 10 . the amount of heat to the vaporizer 21 is controlled by the diverter gate 52 mounted in the exhaust pipe 50 . ideally , the vaporized fuel mixture 25 is raised to a temperature of about 250 ° f . as measured at a probe 60 in the discharge head 39 as it leaves as hot vapor 13 at the top of the fuel tubes 35 . the vaporized fuel mixture 13 is then aspirated through the annular exit 33 and is mixed with warm , filtered main combustion air 14 to form a stoichiometric fuel mixture 17 . the amount of fresh air being mixed with the hot vapor is controlled by a feed butterfly valve 61 mounted inside sleeve 40 . the stoichiometric fuel mixture 17 is directed through a mixing chamber 62 comprising multi - directional blades or vanes 63 to further mix the fuel mixture 17 before reaching the engine intake . a majority of the air required for operation of the engine 10 enters the engine as fresh main combustion air 14 directly into the main air gallery 20 . a conventional air filter 64 is fit to the sleeve 40 . the feed butterfly 61 in the sleeve 40 provides a gross level of control for regulating the quantity of main combustion air 14 in proportion to the rich mixture 25 regulated by the fuel / air regulator 22 . the throttle regulator 15 at the engine intake 11 is controlled through a connection to the gas pedal ( not shown ). the throttle regulator 15 is coordinated with the fuel / air regulator 22 to vary engine output . various other embodiments of the control of main air 14 and rich fuel mixture 13 are illustrated in fig7 a - 7 c . as described above , the feed butterfly 61 grossly controls the main air proportions through the sleeve . in fig7 b , the sleeve 40 may simply comprise a self regulating venturi , without a butterfly . in fig7 c , a venturi 66 can be formed at an inlet to the main air gallery 20 , the venturi having a throat 67 so that the resulting venturi effect may be combined for both proportioning of the air 14 and for creating the low pressure used for drawing the rich fuel mixture 13 into the main air gallery 20 . typically the vaporizer 21 is fitted with a small low - capacity fuel / air regulator 22 such as a mikuni ™ carburetor available from mikuni american corporation of northridge , calif . such a carburetor is typically implemented for use with motorcycles and snowmobiles , and normally not to larger automobiles and the like , including a mikuni hsr42 / 45 series carburetor . as stated , the carburetor provides a rich fuel mixture 25 to the vaporizer 21 for heating by the exhaust gases 31 . the amount of carrier air 24 b in the fuel mixture 25 is non - stoichiometric , that is , the mikuni ™ carburetor does not provide enough carrier air 24 b to provide efficient or complete combustion in the engine 10 . the main air gallery 20 provides the greatest amount of air 14 . the butterfly 61 on the main air gallery regulates the mixture of main air 14 to supplement the rich fuel mixture 25 , 13 provided by the mikuni . in an example a mikuni ™ carburetor was fit to a 350 cu . in . v - 8 engine in a pre - 1990 ½ ton chevrolet ™ truck . the truck had a conventional fuel consumption of 14 miles per gallon ( mpg ) prior to installation of the current invention . afterwards , the performance was increased to 72 mpg .