Installing a new Street Demon
By Sam Logan.
Photos by Moore Good Ink.
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Before the new Street Demons were first released to the public on Friday, May 25, 2012, the carburetor company dispatched twenty to thirty pre-production units to discerning carburetor critics for testing and evaluating. For this purpose Street Demons were sent all over the country—even to Australia.
Tests were conducted at sea level and in the mountains, in cold and in hot conditions, in stop-go traffic and in engines with unfathomable camshaft timing—profiles contrived for noise rather than power. Some even found their way onto towing vehicles, lugging heavy trailers up hills. All testers were invited to “Have at it,” as they say and were actively encouraged to present their findings—warts and all.
One of these pre-production Street Demons appeared at Automotive Service and Performance (ASAP), a hot rod tuning shop in Gainesville, Georgia. Known as the poultry capital of the world, Gainesville nestles in the Appalachian foothills on the shores of Lake Lanier about 50 miles north of Atlanta. It has an elevation of 1250 feet.
ASAP’s Bobby Tow had a 1972 Dodge Dart lined-up and awaiting the fitment of the new Street Demon. The Dart, now owned by Rick Ellis, President of the North Georgia Mopar Club, is one of around 250,000 produced in 1972 and was supplied originally with a Carter two-barrel carburetor, which was replaced by an Edelbrock 600 some years ago. Now the Edelbrock is being replaced by one of the first available Street Demons. Here in this sequence of photographs that follow are the simple steps required to install and tune the new carburetor.
Bobby Tow of ASAP anticipates much potential from the first Street Demon in town.
This 1972 Dodge Dart is mostly original except for the addition of power disc brakes, Mopar Performance valve covers and air cleaner, the Edelbrock 600 carburetor with vacuum secondaries and electric choke, and aftermarket headers and dual exhausts.
The first steps are simple: remove the air cleaner and the two return springs. The leading spring in the tech’s left hand is the accelerator return spring. The other serves as the transmission kick-down linkage tension spring.
Remove the cotter pin and yoke that secures the throttle cable to the linkage stud of the carburetor. The linkage stud is a Dodge part transferred from the original carburetor.
Remove the PCV hose. Positive crankcase ventilation transfers crankcase gases to the combustion chambers, via the intake, where they are consumed. The gases are drawn in under the carburetor throttle blades though a channel in the base plate.
Remove the fuel line and plug it to make it leak proof.
If applicable remove the wires from the electric choke.
Undo the 4 nuts and remove the old carburetor
The dividing wall in the plenum indicates a dual-plane intake manifold—two separate plenums and two separate sets of runners. The strengths of the dual plane over its single-plane counterpart are usually livelier low-rpm response and superior torque production, as well as improved drivability and better idle quality. In a race car, black blemishes like these would be attributed to carbon, indicating poor valve sealing or valve bounce or an overly large camshaft producing significant overlap. On our road-going 1972 Dodge Dart, however, this plenum discoloration is caused by PCV gases.
The chief visual difference between the Edelbrock and the Street Demon on the right is the latter’s Goggle valve. Because of Demon’s decision to employ two small, potent 1-3/8in primary throttle bores, large secondary throttles were essential. However, two conventional round throttle bores would have been too restrictive. Hence the uniquely shaped Goggle valve was born.
The original equipment throttle linkage and kick-down stud is transferred to the Street Demon. In production carburetors this stud will be provided in the kit
Sandwiched between the inner and outer gaskets is a heat insulator. In addition to these the Demon kit consists of the following: Instruction sheet Fuel inlet fitting gasket Assorted throttle balls with nuts Transmission kick-down stud with nut Mounting studs, nuts and washers Air cleaner stud Air cleaner gasket Throttle retainer clip Throttle stud (Short) 5/16” hose barb fuel inlet fitting 3/8” tube Inverted flare fuel fitting Positive choke wire
Set the Street Demon onto the mounting studs and secure it to the intake manifold with the four nuts.
Connect the two choke wires, the fuel line, and the crankcase breather line
Connect the throttle cable clevis and secure it with a cotter pin
Check the choke butterfly for correct operating clearance
With a washer and a retaining clip in place the kick-down linkage is secured to the carburetor
Setting the idle speed is performed by observing the tachometer or listening to the engine sound.
Before making adjustments to the idle mixture screws, always bring the engine to normal operating temperature. The first step in idle mixture adjustment is to turn each screw inward slightly (approximately ¼ turn) to determine if engine speed increases or decreases. If it decreases the idle mixture is too lean; if it increases the mixture is too rich; therefore, slow the idle speed adjuster and adjust the idle mixture screws again, this time using a 1/8th turn inward. Out-of-the box, these idle mixture screws were perfect. Nonetheless, they were adjusted by approximately 1/16th of a turn richer (counter clockwise). This prevents the occurrence of a lean condition while braking. Drawing vacuum potentially causes leanness.
The air cleaner stud 1/4in x 20tpi (provided) is marked and cut to the correct length.
Demon Carburetion’s decision to conduct 20 to 30 independent pre-production carburetor tests led Bobby Tow of the ASAP hot rod shop to conclude, “This carburetor is apt to be good.” Car owner Rick Ellis declared, “The Street Demon surprised me twice: it has superior performance and my fuel consumption improved!”
Automotive Service and Performance
Bobby Tow and Tommy Haley
2141 Hilton Dr
Gainesville, GA 30501