By Ben Mozart
When the original 625 Street Demon was launched in May 2012, it was greeted with much approval—the only thing conspicuously missing, said some, was greater flow capacity.
In appearance the bigger 750 looks identical to its forerunner, except for the size of its primary throttle valves, which have been enlarged in diameter from 1-3/8th to 1-11/16th. The main venturii diameter has also been enlarged. Predictably the calibrations have also been increased.
The secondary throttles, which are controlled by the Goggle valve, remain unaltered. An innovative device located at the bottom of the secondary bores, the Goggle valve delivers over twice the air flow of the primary bores. It maintains an invigorating effect that can be both felt and heard.
Located at the air horn is an adjustable torsion spring-controlled air valve. Its function is to ensure uninterrupted primary-to-secondary throttle response, regardless of the throttle opening rate.
In common with its predecessor, the 750 accommodates square- or spread-bore intake manifolds with an adaptor plate supplied in the drop kit. It also benefits from the 625’s unique fuel bowl that is integrated with the main body. Available in either aluminum construction or in an exclusive automotive-spec composite, the composite bowl demonstrates its drivability credentials particularly in hot stop-start conditions. Because it reduces heat transfer by as much as 20 degrees Fahrenheit, it contributes to faster hot restarts.
To virtually guarantee a leak-proof bowl Demon created it without any plugged passages. Reassuringly, the bowl gasket is placed above the fuel level.
Perhaps the Street Demon’s most enduring talent is its triple-stack venturii. Two of the booster formations are placed across the bores in the conventional way; the third is neatly integrated into the throttle bore walls. Their purpose is calculated to produce superior fuel emulsification, to present crisp throttle response and drivability, and to provide optimum fuel economy.
An easy replacement for any street four-barrel, the purpose of this latest model is to find favor with those who require a little more air and fuel than the 625 is designed to provide. A single fuel inlet ensures simple installation and two-stage metering rods accommodate most tuning requirements, without carburetor disassembly or removal. For cold starting, a reliable electric-assist bimetal coil choke is provided.
Street Demons are available in three part numbers and finishes: P/N 1903, all aluminum tumble-burnished; 1904, tumble-burnished with composite fuel bowl; and 1905 all aluminum hand polished.