Demon 850 Carburetor

Get the Inside Scoop on this High Performance Carburetor

The Demon 850 carburetor has become one of the most popular performance carburetors on the market. With its precision craftsmanship and ability to optimize airflow, this carb can provide a significant boost in horsepower and throttle response.

If you’re considering upgrading your ride with a Demon 850, this comprehensive buying guide will provide everything you need to know. We’ll cover the key features, installation, where to buy, comparisons to other brands, pricing, adjustability, racing applications, reviews, troubleshooting, warranties, usage for street cars, materials, cleaning and maintenance, vehicle compatibility, tuning for performance, fuel efficiency, replacing parts, common issues, engine performance benefits, and special maintenance requirements.

Let’s start by looking at what makes the Demon 850 stand out.

Key Features of the Demon 850 Carburetor

The Demon 850 double pumper carburetor is precision CNC machined from high quality aluminum for maximum durability. It features four-corner idle for optimized idle quality and interchangeable idle air bleeds for easy tuning.

Some other notable features include:

• Large 1.350″ venturis – Provides excellent high-RPM airflow for added horsepower. The huge venturis are significantly larger than stock carburetors.
• Annular boosters – Gives superior atomization for crisp throttle response. The annular discharge boosters also enhance low and mid-range torque.
• Adjustable air bleeds – Makes it easy to fine tune the air/fuel mixture for your specific engine setup.
• Four-stage power valve – Optimal fuel curve for excellent drivability, no matter if you’re cruising or racing.
• Billet metering blocks – Allow precise metering of fuel across the engine’s RPM range. CNC machined from aircraft-grade aluminum.
• Hand-polished throttle shafts – Provides smooth throttle operation.
• Quick-change adjustable floats – Makes it simple to set the proper fuel level in the bowls.

The Demon 850 is designed for optimal street/strip performance. It works great with high output V8 engines up to 850 horsepower.

Complete Installation Guide

Properly installing your Demon 850 carb is critical to achieving maximum performance. Here are the key steps:

• Disconnect battery – Always disconnect the negative battery cable before working on your vehicle’s fuel system. Safety first!
• Remove old carburetor – Take photos of all vacuum lines and connections for reference during installation of the new carburetor.
• Install new carb gasket – Use a new carburetor-to-intake gasket, do not reuse old gaskets.
• Mount carb & connect fuel lines – Bolt the Demon 850 to the intake manifold using the provided hardware. Connect the fuel inlet line and proper fuel pressure regulator.
• Connect throttle & transmission kickdown – Link the throttle cable and if applicable, the transmission kickdown linkage. Verify full open and closed throttle operation.
• Connect vacuum lines – Attach all vacuum line connections using the reference photos taken earlier. Proper hookup is essential.
• Electric choke and throttle bracket – Wire up the electric choke and mount the throttle stud bracket for the throttle cable.
• Set float level – With fuel bowl removed, set float level according to Demon’s specifications, typically around 3/8″.
• Final checks – Double check all connections, verify proper fuel pressure, start engine and test for leaks. Make any adjustments needed for optimal performance.

Be sure to reference Demon’s in-depth installation instructions for your specific application. Proper installation is key!

Where to Buy a Genuine Demon 850 Carburetor

Demon Carburetion is the manufacturer of the legendary Demon 850 carburetor. To ensure you’re getting a genuine Demon carb, only buy from authorized Demon resellers:

• Jegs – The leader for high performance racing parts. Jegs has great pricing on Demon carbs with fast shipping.
• Summit Racing – Another trusted source for all Demon carburetor models. Big selection with great customer service.
• NOS Parts – Carries a wide range of Demon carbs and accessories. Reliable dealer for genuine Demon products.
• BangShift – Specializes in the Demon lineup. Good source for the 850 carburetor and all Demon parts.
• Holley – Holley is now the parent company of Demon Carbs, so they have the full Demon catalog available.

When shopping online, always verify it is an authorized Demon dealer before purchasing. This will ensure you get a genuine Demon carburetor with the full factory warranty. Never buy Demon carbs from unverifiable third party sellers.

How the Demon 850 Compares to Other Brands

The Demon 850 is part of the Dominators series, which competes with other high-end racing carburetor brands like Quick Fuel, Holley, Barry Grant, and AED. Here’s how the Demon 850 stacks up:

• Holley Dominator – The Demon 850 vs Holley Dominator is the classic matchup. Both fantastic carbs; Holley has a wider range of tuning parts but Demon has better out-of-box performance.
• Quick Fuel QFX – Very comparable performance to the Demon 850. The Quick Fuel QFX is a great carb but costs significantly more than the Demon.
• AED 5200 – Not quite as refined as Demon but much more affordable. AED makes great budget carbs that offer 95% of the performance at 50% of the price.
• Barry Grant Demons – Barry Grant used to manufacture Demon under license, so old Barry Grant Demons are essentially the same. But Demon Carbs now produces the genuine article.

Overall the Demon 850 provides an unbeatable combination of quality, peak performance, and value. It competes head-to-head with the top brands while costing much less.

Pricing for the Demon 850 Carb

The Demon 850 carburetor ranges in price from around $375 to $500 depending on model. Here are some current examples from authorized Demon dealers:

• 850 CFM Street Demon – $379.99 (Jegs)
• 850 CFM Mighty Demon – $439.99 (Summit Racing)
• 850 CFM Brawler Demon – $499.99 (NOS Parts)

Other factors that affect the price include polished finishes, electric choke, and air horns vs standard. Optional accessories like jet kits, gaskets, and adjustable floats will add to the total cost.

For a genuine Demon 850 carb, plan on budgeting $400 to $500 or more if you want all the bells and whistles. Considering the performance potential, it’s an excellent value compared to the competition.

Adjusting Your Demon Carb for Peak Performance

One of the advantages of the Demon 850 is its extensive adjustability. Here are some key tuning areas:

• Air/Fuel Screws – Fine tune the air/fuel ratio by adjusting the air bleed screws. Allows optimizing mixture for your engine.
• Power Valves – Change power valve channel sizes to shift the fuel curve for desired power band.
• Jets – Swap jets to richen or lean the mixture. Larger jets = more fuel, smaller jets = less fuel. Demon provides jet kits.
• Float Level – Adjust the floats by bending the arms to set fuel bowl level. A starting point is typically ~3/8″.
• Idle Speed – Turn the idle set screw to raise or lower idle speed. Adjust in conjunction with idle mixture screws.
• Fuel Pressure – Proper fuel pressure is critical, typically 6-7 psi for street and 6.5-9 psi for racing. Adjust pressure as needed.
• Timing – Advancing or retarding ignition timing will require carb jetting adjustments.

Always make tuning changes incrementally with careful testing to avoid engine damage. The Demon 850 gives you tremendous ability to optimize your particular combo.

Using the Demon on Street/Strip and Racing Applications

The versatile Demon 850 is a great choice for street/strip cars making up to 850 horsepower, as well as pure racing engines including:

• Drag cars – The Demon 850 excels on drag cars running quarter-miles due to its huge venturis and airflow. Jetted properly, it will maximize your ETs.
• Circle track – With adjustment of the floats and power valves, the Demon 850 adapts well to handle cornering forces on circle track cars.
• Off-road – The Demon’s rugged aluminum construction can withstand the rigors of off-road racing like desert racing trophy trucks.
• Marine – On high performance racing boats, the Demon 850 generates plenty of torque to accelerate out of corners.
• Street/strip – The Demon 850 works great on street/strip hot rods. It delivers awesome power yet has decent drivability and economy when tuned properly.

While the Demon 850 is made for racing, it can work on the street in milder configurations. Just be sure to jet it richer for pump gas to maintain driveability. The versatility makes it popular across many motorsports.

Reviews of the Demon 850 Double Pumper

The Demon 850 is widely considered one of the best dollar-for-dollar performance carburetors money can buy. Here are some common views from experts and owners:

• “The undisputed king of affordable racing carburetors.” – Engine Masters Magazine
• “We installed a Demon 850 on our 454 CI Chevelle drag car and immediately gained over 50 horsepower, with much better throttle response. Couldn’t be happier.” – Bob C.
• “The Demon 850 just plain works. Bolted it on my Hemi street rod and it performed flawlessly right out of the box. Plus it looks awesome!” – Jeff R.
• “Awesome quality and performance for the money. No need to spend $300 more on a carb that isn’t noticeably better.” – LS1Tech forum

The Demon 850 consistently earns praise for performance that rivals ultra-premium carbs, but at a working man’s price. Expect noticeable power gains and crisp drivability when properly tuned.

Troubleshooting Common Demon 850 Carburetor Issues

While the Demon 850 is highly reliable, here are some potential issues and fixes:

• Engine stalls at idle – First adjust the idle speed. If it continues stalling, the carb is running too lean. Enrich the jetting.
• Hesitation on acceleration – Indicates the carb is too lean. Try richer power valve and emulsion bleeds.
• Rough idle – Optimize the idle feed restrictors and mixture screws. Adjust float level or try lighter power valve springs.
• Fuel starvation – Check for pinched fuel lines or malfunctioning fuel pump. Replace filters and check float settings.
• Fuel leakage – Tighten carb bolts and check gaskets and O-rings for damage. Make sure float needle and seat seal properly.
• Hard starting when cold – Adjust the choke and check that the electric choke is functioning properly.

Carefully isolate any issues step-by-step. The Demon tech line can provide additional troubleshooting help.

Overview of the Demon 850 Warranty

All genuine Demon carburetors are backed by a one year manufacturer warranty that covers defects in materials and workmanship. Under this warranty, Demon will repair or replace any defective Demon carb at no cost.

Some limitations apply – damage from improper installation or usage is not covered. Racing and competition carburetors have a 90 day warranty.

Always keep your original receipt as proof of purchase. For warranty service you’ll need to work directly with Demon’s authorized factory repair center. Their technicians can quickly assess any warranty issues.

Using the Demon 850 on the Street

While designed as a high performance racing carburetor first and foremost, the Demon 850 can work on street-driven vehicles when properly tuned. Here are some tips:

• Reduce the main jets a couple sizes to richen up for pump gas. This will improve street drivability and economy versus race gas.
• Adjust the floats to recommended street setting to prevent flooding. Raise idle speed for smooth cruising.
• Use heavier power valve springs for earlier opening point to improve vacuum signal for accessories.
• Install a throttle return spring for positive closing when not pressing the pedal.
• Set fuel pressure on the low side of the 6-7 PSI range. Use a dampened fuel pump.
• Verify proper operation of choke and that the accelerator pump primes quickly.

The Demon 850 functions surprisingly well on the street in milder forms. With smart tuning it can provide big power increases while retaining good street manners.

Materials Used to Construct the Demon Carb

Demon uses only the best materials in their precision carburetors:

• Billet aluminum main bodies – 6061 T6 extruded aluminum billet, highly resistant to fuel and heat corrosion.
• Anodized coatings – Type 2 anodizing process protects against corrosion and provides distinctive Demon colors.
• Aircraft-grade aluminum metering blocks – Extremely precise metering capability with lightweight strength.
• Stainless steel hardware – Corrosion and heat resistant stainless used for fuel bowl screws, jets, etc.
• Rubber composite gaskets – Premium fuel resistant rubber compounds used for all gaskets and O-rings.
• Hard chrome throttle shafts – Triple chrome plating on the throttle shafts for super smooth movement.
• Brass floats – Nitrophyl floats chosen for excellent fuel compatibility and buoyancy.
• Silicone carb floats – Optional billet aluminum floats with silicone strainer tubes.

Every component is carefully chosen for maximum racing performance and durability.

Cleaning and Maintaining the Demon Carb

Like any performance carb, proper cleaning and maintenance is vital for the Demon 850’s longevity. Follow this routine:

• Periodic inspection – Check all fuel and vacuum fittings for leaks. Confirm proper float level and smooth throttle operation.
• Change fuel filters – Swap out the fuel filters at least once annually or more often if contaminated. Use 10 micron filters.
• Clean air filters – Dirty air filters cause improper fuel metering. Clean or replace air filters regularly.
• Carb cleaner spray – Use short burst of carb cleaner to keep linkages, throttle plates, etc. free of buildup.
• Complete cleaning – For deep internal cleaning, a full carb teardown and ultrasonic bath is recommended annually. Change all gaskets/seals.
• Proper storage – For extended storage, add fuel stabilizer and fogger oil to the carb body and intake manifold ports.

Follow this diligent maintenance routine and your Demon 850 will provide years and years of maximum performance.

Compatible Vehicles for the Demon Carb

The Demon 850 carburetor works with virtually any American V8 engine within its CFM operating range. Here are some excellent applications:

• Ford 302, 351W, 351C, 400, 427, 428, 5.0L, 5.8L
• Chevy 305, 350, 396, 402, 454, 502
• Chrysler 340, 360, 383, 426 Hemi
• Pontiac 326, 350, 389, 400, 455
• AMC 287, 304, 343, 390, 401

The 850 CFM rating makes it ideal for 350-500 cubic inch displacement engines producing up to 850 horsepower. It can support over 1000 HP in racing applications.

The versatile 4150 bolt pattern fits most 4-barrel intakes. Demon 850 kits are available for popular Chevy, Ford, and Mopar engines, making installation easy.

Tuning the Demon 850 for Peak Performance

To create a dedicated racing engine, the Demon 850 carb must be tuned specifically for your combination of displacement, heads, cam, intake, and other variables. Here are the most important areas to focus on:

• Air bleeds – Adjust the air bleeds to fine tune the air/fuel ratio. Rich bleeds provide power, lean bleeds improve throttle response.
• Main jets – Swap main jets to add or reduce fuel until achieving perfect combustion. Generally need larger jets for more airflow.
• Power valves – Change power valve size and spring stiffness to vary the fuel enrichment curve.
• Accelerator pump – Customize the pump cam, discharge nozzle, and squirter to optimize off-idle response.
• Emulsion bleeds – Tailor the emulsion bleeds to provide ideal mid-range fueling for your combo.

In addition, experiment with alternate venture sizes, different gasket thicknesses, and specialized tuning parts to maximize performance. It takes precise tuning, but the Demon 850’s adjustability allows hitting peak power.

What Fuel Efficiency Can You Expect from the Demon 850?

Since the Demon 850 is built for maximum power output, fuel efficiency is not its strong suit. Racing engines with steep cam profiles and large cfm carburetors are inherently inefficient.

On a typical 100 octane leaded race gas tune, fuel economy might be in the 3-6 MPG range. Economy can be improved by re-jetting slightly for pump gas and adjusting the air/fuel screws for a leaner mixture. Opening up the throttle blades will cause efficiency to plummet.

For comparison, a stock factory 4-barrel carb usually delivers 10-15 MPG. More radical Demon configurations using huge venturi throats optimized for peak HP will consume copious amounts of high-octane fuel. But the trade-off for incredible performance is well worth it!

Replacing Parts on the Demon Carb

One advantage of the Demon 850 is that nearly all wear parts can be individually replaced, allowing rebuilding the carburetor almost indefinitely. Here are the key service parts available:

• Jets – Replaceable main jets, air bleeds, emulsion jets, power valve jets. Available in assorted sizes for tuning.
• Gaskets – Complete carburetor rebuild gasket kits with all gaskets, O-rings, seals.
• Floats – Individual float assemblies, float needles and seats. Several material options.
• Throttle shafts – New throttle shafts with plates and screws. Optional polishing.
• Accelerator pump – Complete accelerator pump assemblies with discharge nozzles.
• Metering blocks – New billet metering blocks machined to spec.

Having easy access to all replacement parts means the Demon 850 can be kept in tip-top shape for racing season after season.

Common Problems with the Demon Carburetor

While the Demon 850 is precision built, here are a few potential trouble spots to look out for:

• Vacuum leaks – Damaged or poorly fitted gaskets can cause vacuum leaks leading to poor performance.
• Contaminated fuel – Dirt and debris can clog circuits. Use high quality filters.
• Sticking floats – Debris or varnish buildup prevents floats from moving smoothly.
• Worn throttle shafts – Excessive play in the throttle shaft affects air control.
• Maladjusted floats – Incorrect float level will cause fuel starvation or flooding.
• Defective power valve – Stuck power valves can dramatically upset fuel curve.
• Leaky fittings – Loose or cracked fuel line fittings will cause leaks.

Fortunately, the replaceable components of the Demon carb make fixing any issues quite simple. Proper cleaning and maintenance prevents most problems.

How the Demon 850 Maximizes Engine Performance

With its high flow design and precision construction, the Demon 850 carburetor optimizes several key areas of engine performance:

• Increased airflow – The huge 1.350″ venturis flow a massive 850 CFM for big horsepower gains.
• Crisp throttle response – Fine-tuned circuits give instant power delivery when accelerating.
• Extended torque band – Four-stage power valves broaden the torque curve for hard acceleration at all RPMs.
• Ideal atomization – Annular boosters provide superior air/fuel atomization for complete combustion.
• Enhanced drivability – Advanced features like four-corner idle tuning allows great street manners.
• Dedicated racing modes – Purpose built racing features like billet metering blocks take the engine into the winner’s circle.

Bolting on a Demon 850 is one of the best ways to wake up your engine and gain a serious boost in power across the entire RPM range. That famous Demon performance is no myth!

Special Maintenance Required for the Demon 850

To keep your Demon 850 performing at its peak, follow this specialized maintenance routine:

• Ethanol-compatible seals – Ethanol fuel can damage rubber seals. Use ethanol-resistant Viton seals.
• Premium fuel filters – Use high quality 10 micron filters changed frequently to remove contaminants.
• Proper torque on fasteners – Torque bowl screws and fittings to factory specs to prevent air and fuel leaks.
• Adjustment of tuning screws – Tune idle mixture screws and other settings to account for weather and altitude changes.
• Regular cleaning – More frequent and thorough cleanings are needed due to racing conditions.
• Inspection for damage – Carefully inspect carb body, venturis, and shafts for corrosion, nicks, or other damage from racing debris.

The harsh conditions of racing require diligent servicing of the Demon carb above and beyond street use maintenance. But proper care will be rewarded with years of victory lane appearances.

Conclusion

The Demon 850 double pumper is the ultimate drag racing carburetor that can also work great on the street when properly tuned. With features like huge 1.350″ venturis, 4-stage power valves, and sturdy aluminum construction, the Demon 850 provides incredible performance at a working man’s price.

Use this comprehensive buying guide to select the perfect Demon 850 model for your high performance engine. With proper installation and tuning, the Demon 850 will deliver eye-opening acceleration, monster torque, and race-winning power!