Despite the fact that we live in the high-tech world of the 21st century, there's still room for a new idea or two, even in the world of carburetors. And so it is that Demon Carburetion, which is back in business, thank you, has come out with a brand-new carburetor, appropriately named the new Street Demon. Appearances tell us it's clearly not a fluffed-up version of the old Demon but a new casting. It's a bit of a hybrid that takes proven, fuel-mixing ideas from the old Carter air-valve secondary (AVS) carbs and the Thermo-Quad, combining them with a couple of new wrinkles to improve part-throttle driveability. Speaking of which, we bolted this carb (PN 1901) to our '65 El Camino equipped with a 290hp Chevrolet Performance crate engine that is modified with a Comp Cams Thumpr camshaft. The El Camino sports a four-speed and 3.08:1 gears, which makes this a serious low-speed carb-signal test and a major party foul with its combination of a big overlap camshaft and tall rear gears. Every previous carb we've tried stumbled badly off idle just as the clutch engaged. This carb also experiences a lean stumble out of the box, though it recovers much more quickly than the other carburetors, and we might be able to remedy the issue with accelerator-pump-squirter or power-valve-spring mods. Speaking of part-throttle tuning, this carb should be a little easier in that regard, as it allows changing the primary metering rods and enrichment springs (which operate much like a power valve) without having to disassemble the carb. This makes the Street Demon one of the easier carburetors to tune for better street manners. Perhaps best of all, the basic 625 Street Demon is priced less than $350. So there are several reasons to like this new Street Demon. Parts List Description PN Source Price Street Demon 625 1900 Summit Racing $349.95 Street Demon 625 w/ polymer insert 1901 Summit Racing 379.95 Street Demon 625, hand-polished 1902 Summit Racing 449.95 1. This new Street Demon is equipped with the optional phenolic center-body housing that promises cooler fuel, which should result in better driveability. The Street Demon reduces leak paths, since all the fuel is located in the center body with a gasket above the fuel level. Also, note the revised, spring-loaded air-valve secondary door. If the top portion of the carb looks clean, that's because there are no exposed fasteners; it comes apart from the bottom. The dual bolt-pattern baseplate fits both standard square flange and the spread-bore Q-jet pattern.1. This new Street Demon is equipped with the optional phenolic center-body housing that 2. Demon calls this a Triple Stack booster. The idea is that stacked boosters increase the signal (or pressure drop) across the outlet, which introduces main-circuit fuel earlier than single-booster designs. If this sounds like an idea straight out of the school of Quadrajet design, it is. The smaller, 1-3/8-inch Street Demon primary throttle bores increase velocity for crisper throttle response.2. Demon calls this a Triple Stack booster. The idea is that stacked boosters increase th 3. As with Carter-style carburetors, each primary metering rod and spring is accessible from the top by loosening one screw. The metering rods are not interchangeable with earlier Carter carburetors. We know because we tried it. The stepped metering rods (arrow) maintain lean air-fuel ratios in high manifold-vacuum cruise applications. Separating the springs from the metering rods allows finite tuning, which can deliver excellent results.3. As with Carter-style carburetors, each primary metering rod and spring is accessible f 4. Demon calls the revised secondary throttle plate a Goggle Valve Secondary (GVS) that is intended to increase airflow. The center peak is designed to clear the divider plate in dual-plane intake manifolds. As a result, the Street Demon will bolt right on a typical Holley square-flange dual-plane intake manifold without requiring an adapter.4. Demon calls the revised secondary throttle plate a Goggle Valve Secondary (GVS) that i 5. The arrows indicate an innovative Street Demon idle modification that should improve idle quality. Demon engineers say these slots introduce a calibrated amount of air across the location where idle fuel exits the carburetor. These idle air ports shear the fuel, which helps with distribution. In theory, this could allow the engine to idle with improved stability at a leaner idle air/fuel ratio.5. The arrows indicate an innovative Street Demon idle modification that should improve i 6. Demon also offers this optional Throttle Valve cable bracket for older, non-electronic 700R4 and 200-4R transmissions that require a TV cable input. The carburetor linkage offers three different positions for the TV cable point. In this photo, the leading hole is for a TH350 kick-down, while the middle hole is the recommended position.6. Demon also offers this optional Throttle Valve cable bracket for older, non-electronic SOURCES Demon Carburetion 270-901-3346 www.DemonCarbs.com By Jeff Smith Enjoyed this Post? Subscribe to our RSS Feed, or use your favorite social media to recommend us to friends and colleagues!
