Demon Fuel Systems SPD-850-VS | Carburetor

Part Number
Speed Demon Carburetor; 850 cfm; Demon 4150 Vacuum Secondary; Down Leg Booster; For 302-427 CID Engines w/Cam Profiles Between 220-240 Deg. Duration At 0.050 in.
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The Mighty Demon is perhaps the best value for the dollar in the carburetor market today. It is available in a full range of sizes and directly replaces the Holley HP Models. It features billet aluminum metering blocks/billet aluminum baseplates/large capacity fuel bowls completed with patented sight glasses and patented streamlined air entries. Some of these features are found only on modified carburetors costing much more and several are available only on Demon Carburetors. These innovative ideas allow the new Mighty Demons to produce more power and achieve higher levels of performance than conventional designs. All Mighty Demon carburetors come with a General Competition tuneup but can be easily modified using BG Fuel Systems carburetor service and tuning parts. For high output street engines and for race engines the Mighty Demon delivers the best performance value for the dollar.

BRAND: Demon Fuel Systems


  • Holley Performance Emission Code 3: This part is legal for sale and use on Uncontrolled (Non-Emissions Controlled) Vehicles and Racing Use Only Vehicles. The following vehicles are considered Uncontrolled (Non-Emissions Controlled) Vehicles: 1965 and older U.S. manufactured California Certified vehicles/1967 and older U.S. manufactured Federally Certified vehicles/1967 and older Foreign manufactured vehicle. The following vehicles are considered Racing Use Only Vehicles: Racing Use Only Vehicles are vehicles that are used exclusively for competition and that are not registered and that may never be used on the street. WARNING: It is against the law to install this part on an Emissions Controlled Vehicle. The following vehicles are considered Emissions Controlled Vehicles: 1966 and newer U.S. manufactured California Certified vehicles/1968 and newer U.S. manufactured Federally Certified vehicles/1968 and newer Foreign manufactured vehicle
  • 850 Speed Demon-Vac Sec-Down-Leg (Designed for mild engines from 302-427 cid with cam profiles between 220 and 240 degrees duration at 0.050in.)
  • Fuel Bowls Now Have Dual Threaded Inlets On Each Side
  • Secondary Fuel Bowls Include Notched Floats
  • Changeable Idle High Speed Air Bleeds
  • Redesigned Throttle Lever w/Integrated Kick Downs Options
  • With Billet Metering Blocks And Base Plates
  • Speed Demon Carburetor
  • Changeable Power Valve Restrictions For Precise Tuning
  • Speed Demon Carburetor; 850 cfm; Demon 4150 Vacuum Secondary; Down Leg Booster; For 302-427 CID Engines w/Cam Profiles Between 220-240 Deg. Duration At 0.050 in.;
  • All Aluminum Polished Construction
  • Billet Baseplate Allows Precision Fine Tuning Of Idle Speed
  • Complete Reengineered and Re-Calibrated
  • Fuel Bowls and Main Body Have A Sleeker More Style Appearance


Billet ColorShiny
Booster TypeDown Leg
EmissionWithout EGR
FlangeSquare Bore
Fuel InletDual
Fuel System TypeCarbureted
Fuel TypeGasoline
High Speed Air Bleed28
Idle Air Bleed Size70
Primary Main Jet68
Primary Power Valve6.5
Primary Pump Nozzle Size31
Secondary Main Jet78
Secondary TypeVacuum
Supercharged ApplicationNo
Throttle Bore1.688 in.
UsageRacing/Circle Track
WARNING CA Proposition 65Yes
WARNING CA Proposition 65 MessageWARNING: Cancer and Reproductive Harm -


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