Demon 4 Barrel Carburetor

Rev Up Your Ride With the Ultimate Performance Carb

The Demon 850 carburetor is a high-performance 4-barrel carburetor designed to deliver maximum horsepower and acceleration. This venerable carb has been a favorite on the drag strip and street for over 50 years, prized for its versatility, adjustability, and sheer power.

If you’re looking to hot rod your classic muscle car or upgrade your off-road vehicle, the Demon 850 should be at the top of your list. This buying guide will walk you through everything you need to know about this legendary carburetor.

Overview of the Demon 850 Features

The Demon 850 packs a 850 cfm flow rate, making it ideal for engines producing up to 650 horsepower. It’s available in manual choke, electric choke, and double pumper configurations. Key features include:

• Four-barrel design with center-hung floats for consistent fuel flow
• Interchangeable high-flow venturi clusters
• Adjustable air bleeds for tuning fuel curve
• Billet metering blocks for precision fuel metering
• Multiple idle and high-speed air correctors
• Changeable emulsion bleeds for fine-tuning
• Vacuum operated secondary throttles for crisp acceleration
• Durable and lightweight aluminum construction
• Compatible with alcohol fuels like E85

With so many adjustments, the Demon 850 can be calibrated for everything from street/strip engines to blown race motors. The components are quality throughout, making this a carb built to last.

Step-by-Step Installation of the Demon 850

Installing the Demon 850 takes time and care, but can be managed by any competent gearhead. Here are the key steps:

• Remove the existing carburetor and clean the mounting surface. Inspect all fuel lines, filters, and pumps for damage or leaks.
• Bolt on the new carb using a new gasket, ensuring proper alignment. Connect all fuel lines, transmission kickdown cables, and throttle linkages.
• Connect vacuum lines for the power brakes and advance. Install a new air cleaner and filter.
• Prime the carb by adding fuel down the vent tubes until it’s full. Crank the engine and check for leaks.
• Make initial timing and idle adjustments based on Demon’s recommendations.
• Adjust the float level, fuel pressure, and mixture screws according to your setup.
• Road test the vehicle, fine-tuning as needed until optimal performance is achieved.

Taking your time during installation and tuning will ensure maximum performance and reliability from your new Demon carb.

Where to Buy a Genuine Demon 850 Carburetor

Genuine Demon carbs and parts are sold through authorized retailers to ensure you get a brand new carb, not old stock. Recommended sources include:

• Direct from Demon Carburetion – Order straight from the manufacturer at DemonCarbs.com
• JEGS – Large selection of Demon carbs and tech support available
• Summit Racing – Hundreds of Demon carburetors in stock, discounted prices
• Holley – Now owns Demon, may have additional tech resources
• Local speed shops – Support small businesses while inspecting in person

Shop around for the best price, but be wary of used or counterfeit carbs from disreputable sellers. Paying a bit more for a guaranteed new carb from an authorized source is worth it.

How the Demon 850 Compares to Other Performance Carburetors

The Demon 850 is part of the holy trinity of performance carburetors, along with the Holley Double Pumper and Barry Grant Demon Dominator. Here’s how the Demon 850 stacks up:

• Holley Double Pumper – More brand recognition and availability, but the Demon flows more CFM.
• Barry Grant Demon Dominator – Similar features and CFM, but the Demon has better throttle response.
• Edelbrock AVS2 – Great street carb but limited to 500 CFM, not enough for big power builds.
• Quick Fuel Technology HR Series – Newer design with modular components, but unproven long-term.

The Demon 850 hits the sweet spot of huge flow with crisp throttle response and bulletproof reliability. While every carb has its fans, the Demon remains the choice for uncompromising performance.

Typical Price Range of the Demon Carburetor

As a premium racing carburetor, the Demon 850 commands a steeper price than economy street carbs. Expect to pay:

• $400-$800 – Basic rebuild kits, gaskets, floats, and hardware
• $900-$1,200 – Complete non-choke manual carburetors
• $1,000-$1,400 – Electric or dual-inlet choke carbs
• $1,100-$1,600 – Fancy annodized or polished versions
• $1,200-$1,800 – Fully prepared race Demon carbs
• $400-$600 – Used and rebuilt Demon 850 carbs

Of course, exotic big dog Demon carbs like the 1150 or 1350 models can demand over $2,000 out of the box. But a street-friendly 850 CFM model will deliver performance worthy of the investment. Compared to paying a machine shop $500+ just to blueprint a stock carb, the Demon provides outstanding bang for the buck.

Adjusting the Settings on the Demon Carburetor

One of the Demon carb’s biggest assets is its extensive adjustability. Fine-tuning your particular setup is key to getting the most from these carbs. Some key adjustments include:

• Float Level – Start with the factory recommendation, then adjust for optimal fuel flow.
• Fuel Pressure – Run 6-8 PSI for street cars, 10-12 PSI on racing engines.
• Air Bleeds – Change bleed size to richen or lean out the fuel curve as needed.
• Emulsion Bleeds – Swap bleeds to alter fuel delivery across the RPM range.
• Metering Blocks – Change bleed size for major fueling changes or when switching fuels.
• Air Correctors – Adjust the curb and high-speed air correctors for idle quality and WOT power.

Don’t be afraid to experiment – the adjustability of the Demon carb is made to be tuned. Keep good notes and make changes one at a time.

Using the Demon on Street Cars vs Race Cars

With some adjustments, the Demon 850 can provide awesome performance on both street/strip cars and competitive racers:

• For street use, opt for a choke-equipped model for easier cold starts. Use a lower fuel pressure, smaller venturi clusters, and richer jetting to maintain crisp throttle response and efficiency during street cruising.
• For racing use, run no choke and an open venturi design optimized for maximum airflow. Run tighter clearances, change emulsion bleeds for higher RPM power, and crank up the fuel pressure.
• For dual purpose builds, use the electric choke model and keep an intermediate setup between street and racing configurations. Swap jets and air bleeds when switching duties. Stock up on carb components to make tuning quick and easy.

While the Demon 850 is ideal for racing, smart adjustments can tame it for the street while retaining incredible performance potential.

Reviews of the Legendary Demon Carburetor

The Demon carburetor has achieved legendary status among performance enthusiasts thanks to its outstanding real-world results. Here are just a few rave reviews:

• “Perfect carb for my nitrous-fed 572 big block Chevy stroker. Over 900 horsepower on the bottle and flawlessly tuneable across the RPM range.”
• “I will never run another carb brand in my drag cars. The Demons gave me 200 extra horsepower over my old double pumpers.”
• “My 454 sounded like it was clearing its throat before the Demon. Now it screams like a demon at wide open throttle. Exactly what I wanted!”
• “Saved me 3 tenths on my quarter mile times. The quick throttle response is so much better than other big CFM carbs.”

The universal sentiment is that the Demon carb provides massive flow along with crisp, instant throttle response that other brands can’t match. Just be ready to tame all that newfound horsepower!

Potential Issues and Troubleshooting the Demon Carb

While robustly built, the Demon 850 is still a high-performance racing carb that demands careful setup to avoid issues. Here are some potential problems and solutions:

• Hard starting – Check choke operation, adjust float level and fuel pressure. Increase primary jet size.
• Bog or hesitation – Float level may be too high, flooding the engine. Check for vacuum leaks.
• Poor fuel economy – Tighten air bleeds and richen up the jetting for improved cruising A/F ratio.
• Black smoke – Indicates overrich condition. Lean out the carb with smaller jets and air bleed adjustments.
• Surging idle – Adjust the mixture screws and curb idle air correctors. Verify proper ignition timing.
• Cuts out or backfires – Usually an excessively lean condition. Rich up the carb or inspect for vacuum leaks.

The Demon 850 responds very well to tuning adjustments, so don’t hesitate to break out your screwdrivers and get the carb dialed in perfectly for your engine.

Warranty Coverage on Demon Carburetors

Genuine Demon carbs sold through authorized retailers are backed by a one year limited warranty covering defects in materials and workmanship. This protects against the rare new carb that slips through quality control with damage or flaws.

Make sure to keep the original receipt or invoice to validate your purchase date and warranty coverage. Demon and their dealers stand behind their products and have excellent customer service should issues arise with a new carb.

However, problems from improper installation, tuning, or lack of maintenance are not covered under warranty – that responsibility falls on the end user. So make sure any carb problems aren’t due to external issues before attempting a warranty claim.

Using the Demon 850 on a Street Car

Many gearheads believe a temperamental 850 CFM Double Pumper carb is too wild for street use. But the Demon carb is actually quite streetable with some smart setup choices:

• Opt for a manual choke or electric choke model for easy cold starts.
• Keep fuel pressure under 7 PSI for improved drivability.
• Use smaller venturi clusters meant for street/strip use.
• Keep primary jetting somewhat rich for low speed and cruising efficiency.
• Limit throttle travel with adjustable linkage to avoid over-revving.
• Run stock fuel pump and normal octane street fuel.
• Upgrade to a baffled racing fuel cell to prevent fuel slosh.
• Set lash on vacuum secondaries for a more gradual engagement.
• Maintain proper ignition timing and use heat range matched spark plugs.

The Demon 850 may sound excessive for a street engine, but it’s right at home providing tire-melting power even during daily driving. Proper tuning keeps it from being an ornery beast.

Construction Materials in the Demon Carburetor

The materials and workmanship that go into the Demon carburetor set it apart from cheaper budget castings. Key components include:

• Billet aluminum main body – Strong, lightweight, and beautifully CNC machined
• Stainless or anodized aluminum throttle plates – Resist corrosion and wear
• 7075 or 6061 billet aluminum metering blocks – Hard anodized for durability
• 2024 aluminum float bowls – Lightweight but strong, black hard anodized finish
• 302 stainless steel internal throttle parts – Resists wear and throttle sticking
• Viton or Buna-N gaskets and o-rings – Resist heat and alcohol-based fuels
• Reinforced composite or Acetal resin floats – Provide consistent fuel delivery

No cheap pot metal or brittle castings here – the Demon is built from quality materials designed for hard use, with beautiful chrome-like finishes that last. This exacting construction is what you’re paying for.

Cleaning and Maintaining the Demon Carburetor

Keep your Demon carb running in tip-top shape by following some basic maintenance practices:

• Use only new clean fuel, and install a quality inline filter before the carb.
• Periodically remove the bowls and spray out the fuel passages and jets with carb cleaner.
• Check and tighten all external fasteners, brackets, fuel fittings and vacuum lines.
• Inspect the throttle shafts and plates for tightness and any sticking or binding issues.
• Use compressed air to clear out idle passages as needed to eliminate any roughness at lower RPMs.
• Visually inspect float bowls for any debris or contamination before final reassembly.
• Verify proper float level and smooth free motion of the floats when disassembled.
• Apply carb lube only where specified by Demon – avoid lube where not recommended.

Regular inspection and cleaning when tuning or rebuilding will keep those massive CFM flowing optimally through your Demon.

Vehicle Compatibility and Optimal Use

The Demon 850 makes an outstanding performance upgrade for:

• Classic muscle cars – Chevelle, Camaro, Mustang, Charger, etc. The Demon 850 can far outflow any original carb.
• Hot rods – With blowers, nitrous, or big cubic inch stroker motors, the Demon feeds massive power demands.
• Trucks/SUVs – The legendary Demon delivers tire frying horsepower in lifted street trucks.
• Drag racers – Pro Stock, Pro Mod, Top Sportsman, bracket racers all run Demon carbs for maximum performance.
• Off-road – Demon carbs provide consistently superior airflow for hill climbing, mud running, and desert racing.
• Marine – On high performance cigarette boats, the Demon supplies unending airflow at wide open throttle.

Wherever you need a carburetor to feed an engine producing 500 HP or more, the Demon 850 likely is the ideal choice. It pairs perfectly with aggressive camshafts, big cubic inch motors, and high compression ratios.

Tuning the Demon 850 for Optimal Performance

Getting the most from your Demon 850 comes down to precise tuning:

• Record baseline readings for fuel pressure, ignition timing, air/fuel ratio, and jetting specs with your current combo.
• Adjust air bleeds in minor increments to tweak the fuel curve throughout the RPM range. Document before/after changes.
• Swap in different metering blocks with alternate flow characteristics if needed.
• Emulsion bleeds alter the transition from low to high speed. Watch A/F ratios and temperature at these points.
• Check float levels and make sure you’re running the fuel system at the PSI the carb was designed for.
• Monitor vacuum at idle and steady highway cruise to detect any leaks.
• Read spark plugs for proper coloration after tuning changes. Force the carb rich/lean and note the differences.
• Don’t overlook ignition timing – an inaccurate distributor curve hampers any carb tuning.

The Demon 850 begs you to experiment until you find the magical combination that unlocks the full potential of your engine. The sky’s the limit!

Fuel Efficiency with the High Flow Demon Carb

The tradeoff for the Demon 850’s incredible peak horsepower is usually reduced fuel economy versus a smaller street carb. However, some tactics can help maximize mpg:

• Limit throttle motion and use tall gearing to keep RPMs low during cruising
• Set lash on the secondary throttles for a more gradual engagement
• Run smaller venturi clusters optimized for street/strip use
• Tighten up air bleeds and richen jets for improved idle and cruise A/F ratios
• Adjust timing for maximum efficiency – total advance around 34-38 degrees
• Consider an electric choke model to avoid manual warm-up enrichments
• Upgrade to an aluminum high flow intake manifold to smooth airflow
• Maintain consistent float level and fuel pressure for optimal mixture
• Avoid aggressive camshafts that reduce vacuum and sip too much fuel at low RPMs

The Demon 850 may never match a 500 CFM economy carb for fuel mileage. But intelligent tuning can keep gas costs under control when you exercise some restraint with your right foot.

Replacing Wear Parts on the Demon Carburetor

As a high-performance carb under stress, maintaining your Demon with fresh components is wise insurance:

• Metering blocks – Replace with new blocks or custom tune by swapping emulsion bleeds.
• Needle and seat – Should provide years of service but cheap insurance to swap in new ones during rebuilds.
• Floats – Upgrade to super durable composite floats that won’t soak up fuel.
• Throttle shafts – Worn shafts allow unmetered air and should be replaced.
• Jets and bleeds – Always start tuning with a fresh set of known good jets.
• Gaskets and o-rings – Use new Viton components designed for performance carbs.
• Vacuum secondaries – Rebuild kits available to refresh sticky or tired parts.

Periodically refreshing these affordable components keeps the precision tolerances of your Demon tight and prevents erratic operation from worn parts. You invested big bucks in this carb, so keep it in top form.

Potential Demon Carburetor Issues to Watch For

While extremely robustly designed, like any high performance carb, there are some potential trouble areas on the Demon to keep an eye on:

• Sticking floats – Ensure floats move freely and don’t bind that could lead to flooding.
• Leakdown or “flat-spotting” – Replace worn needle and seat to maintain consistent fuel delivery.
• Vacuum leaks – Inspect all hoses, gaskets, and throttle plates for cracks or looseness.
• Binding secondary throttles – Disassemble and lubricate linkages, replace worn parts.
• Perforated or torn diaphragms – Any small holes cause vacuum leaks and require replacement.
• Jet blockages – Carefully inspect jets for contaminants blocking fuel flow, especially the power valves.
• Throttle sticking – Lube shafts, replace worn components, adjust linkage to prevent binding.
• Fuel leakage – Ensure bowls are tightened fully and gaskets/seals in good condition.

Regular inspection and maintenance helps reduce the likelihood of issues occurring down the road. The Demon carb will provide years and years of trouble-free performance when properly maintained.

How the Demon Improves Performance

The Demon 850 carb provides multiple performance benefits compared to most stock or street replacement carbs:

• Greater airflow – The large venturi design flows up to 850 CFM, supporting over 650 HP. Far greater than an OEM 600 CFM carb.
• Tunable fuel curve – Changeable air bleeds and emulsion bleeds allow tuning the fuel profile for any engine combo.
• Superior throttle response – Quick reacting vacuum secondaries and optimized fuel channels provide instant power.
• Consistent fuel metering – The billet metering blocks and floats maintain precision control of the air/fuel mixture.
• Reduced restriction – Large venturis and smoothing contoured bowl design allows air to flow unimpeded.
• Strength – Billet aluminum body and hardened components are built for extreme duty and high RPM operation.

No question, bolting on a Demon carb instead of a stock replacement is one of the best bang-for-buck power upgrades available. That giant 850 CFM flow turns would-be pony cars into fire breathing monsters.

Special Considerations for the Demon Carb

The Demon 850’s razor sharp performance requires some specific maintenance considerations:

• Requires perfectly clean fuel supply – high volume inline filters are strongly recommended.
• Must run recommended fuel pressure – double check your regulator is providing the PSI required.
• Proper vacuum secondaries setup is crucial – improperly adjusted will result in poor street manners or bog.
• Hardened seats and Viton tipped inlet needles prevent alcohol fuel damage – never run standard components with race fuel.
• Keep extensive tuning notes – record all adjustment changes to allow accurately returning to previous settings.
• Safety first when tuning – nitrous backfires or lean-popped demon engines can seriously injure careless carb tuners. Wear eye protection!

Respect the Demon’s potential and pay close attention to these special tuning needs. Your patience will be rewarded with a perfectly optimized performance carb.

Wrapping Up the Demon 850 Carburetor Buying Guide

This venerable performance legend has stood the test of time, gracing the world’s fastest street cars and baddest race cars alike. Tunable response, fuel curve flexibility, and outright massive airflow validate the Demon 850’s status as a top carburetor for serious horsepower.

While requiring thoughtful tuning and setup, properly installed and adjusted, a Demon carburetor will reward you with tire obliterating power. If you’re ready to unleash your engine’s full potential, the Demon 850 is likely your carburetor soulmate. Just make sure you have the skills to keep this beast fed and happy!