How To Lean Out A Holley Carb


Troubleshooting Your Holley Carb August 2, 2017 Wayne Scraba Fuel Delivery , How-To and Tech Tips , News 1 Holley carburetors find their way onto countless vehicles, from race cars to hot rods to delivery trucks, and for good reason: They’re the standard of performance, and without question some of the most popular and easily tunable. This is very important, since if you allow the engine to overrichen on the line and the temp of the combustion chamber drops , you can cheat yourself out of an easy 25 to 100 HP depending on the size of the engine. Holley points out there is a chamfer around that hole that has a strong effect on what that jet flows. Also since it's a "centrifugal" style charge, you need to make sure that carb hat isn't leaking anywhere if you were spitting fire out of the exhaust, and lean backfiring you could have been doing the same out of the carb which in turn could ave blown apart some of the hosing, causing a leak between the super charger and the carb hat, or. Screw the idle control screws in or out will allow more or less (emulsified) fuel to exit the carb. 3 plus a Holley 2 bbl. My engine builder (he is 52 and a very good friend) Gave me an old race carb (because hes not a fan of vac sec. If used, these early BSA & Triumph carbs should also have 622/235 update kit installed. In order to truly tune my carb, I want a better understanding of the symptoms of lean vs the symptoms of rich. The M4M is the emissions Q-Jet introduced in 1975, which has had certain adjustability added in while some of the off-idle power transition is taken out. out and installed just a regular electric pump straight to the filter to the Carb. Any further in and it will stall or hesitate at the snap of the throttle. Holley carbs come with a standard shooter size which differs by carb list#. The best way to set the idle mixture is to lean the carb out until the vacuum just starts to drop, then richen the mixture by about 1/4 turn. Though it started and ran good, it was dumping fuel and would not lean out to AFR set points. i don't know if you have solved your carb prob yet or not, but if not, we have a great sponsor-Bigs Performance Carbs, from altoona, wisconsin, we used a 4412 that they sponsored to us last year on our street stock, and never had one prob with it at all. I'm sure 95% of everyone on here had to order theirs. A Holley carburetor can be leaned either through the idle circuit or the main jets. turn it back out till it runs smooth and keep turning out till it again runs poorly. Your going to have just as many problems tuning a holley to maximum performance with any carb you get, edelbrock work fairly well out of the box. It is a very common carb for IH vehicles. fuel pressure. Clockwise will lean the idle mixture, counterclockwise will richen the mixture. 302 bored 0. A bad vacuum leak can lean out the mixture enough to cause an engine backfire. it backfires real bad (and fast) when driven, hopefully i havn't broken anything yet. Getting hot along with less lube is generally a bad thing. That is great that Summit carries the idle feed restrictors. Lose the BBD - 318 2bbl to 4bbl Conversion: Trucks & 4x4 : Some time ago, I realized that I, like many people, had a vehicle powered by a Chrysler 318 cubic. The bog or hesitation may be caused by a momentary lean condition when the carb goes from the idle throttle position to the main metering system. When I give a very light throttle input, with on take off or while cruising, I have a lean spot (verifyed with an O2 meter) hich is causign the car to stutter for a second or too. The only way I know to lean out the carb is to read your plugs and jet down or up to get it right. I'm of the opinion that the Edelbrock carb is capable of delivering better power with better fuel economy than a Holley. Think siezed pistons and chewed out bearings Running too rich will usually smoke and lack power, it will foul up spark plugs and smoke you out, but it shouldn't kill the saw. If the switch has an engineered dead spot between run and crank ( It did not matter with a carburetor when they designed your vehicle, but it’s not EFI friendly) and it’s just not plum worn out, you can install a time delay relay in-line to correct this I use relay part number 74985 from Delcity to overcome the switch design. 302 bored 0. Jets are broached. I'll second that! When I got my 55, it's mild 350 had a 1407 carb on it. Vacuum leaks come to mind. tromp on it hard and it will lean back fire out the top of the carb on these carbs try to read the instructions up front there are a few measurements you want to know about first the metering rod assembly is adjustable under this aluminum plug so it is important when you get it out to measure it. If you bought a new 650 or 700 BG Race Demon double pumper, the difference between that and a standard Holley carb is very noticeable. It will require that idle screw is turned to increase RPM for the cylinder to be adjusted. I was amazed at how well the car ran with this carb straight out of the box. I'm sure 95% of everyone on here had to order theirs. Take the plugs out and if they look clean you're good to go. My replacement carb ran great, so they're good in that aspect, and I image if you're a bolt on and go kind of guy, you'll never run into this issue. secondaries. The car will idle in the garage for an hour and barely make it to 180 degrees, but at the track within 5 laps the temp is 230. It will vibrate out of adjustment if your needle valve clamp nut is not tight enough. No missing. Remove main jets and inspectfor foreign matter and proper size stamped on side. I finally got around to remove my holley 750 and putting on my speed demon 750 dp. Hesitation under heavy throttle: Deadspot & stumble. RE: Holley Idle Circuit Mods - Mustangmike - 11-04-2015 Hey Mike, I needed to cross reference the part number on the carb to get the model # on Holley's site. Backfiring through the carb can be an indication of being too lean - this is not a good thing for your blower build. Though it started and ran good, it was dumping fuel and would not lean out to AFR set points. This carb was used on my roadster before switching it out for a 750HP Holley. WOT – Anything over about half throttle reduces manifold vacuum to a point where the power valve should open. To provide additional fuel for high power or high load situations, Holley type carbs utilize a power valve circuit. Almost everybody has a Holley carb but not everyone know how to tune them we show you how and help you learn the science and basics of carburetors. 2 wiht the carter carb and it is running way to rich. The list of all the classic Holley carburetor numbers from the 1930s to 1980s with applications and OEM numbers as well as kits, floats, chokes and manuals is here. This is how I baseline a Holley 4150 Double Pumper carburetor. After talking to Holley tech, I replaced the factory regulator and problem solved. If you bought a new 650 or 700 BG Race Demon double pumper, the difference between that and a standard Holley carb is very noticeable. 3:1 (lambda 1. If I lean it out too much there are a couple cylinders that are fuel starved (too lean) and start to misfire. With a holley, you may need to rejet it, replace the air bleeds, power valve to adjust the mixture to a leaner conditions. The info that Gert sent in contains info on how to adjust holley floats, a high float level will cause a rich condition and low level will lean it out. One trick that works well with Broncos is to use the heat activated switch originally intended to open the EGR diaphragm, if you are no longer using it, you can use it to act as a vacuum advance delay. As you drill them out you will be required to turn the idle mixture screws out to regain good idle control. There are several options out there for that. As a starting point, set the needles 1 1/2 turns out from the full lean position, and then adjust for best idle. Harley Carburetor Jets Hello and I love all the info from this site as I have learned a lot from it. It's acting up. Please help. need some advice on tuning a weiand tunnel ram with 2 new out of the box holley 600 vac. Turning them in will restrict the flow of fuel to the idle circuit and lean the mixture. Starting at: $325. I think mine is a 4160 Holley, but its been 7-8 years since I added and tuned it to the engine. Everything is brand new and has 400 miles on it. Carb was fully rebuilt, specifically for my motor by a very reputable shop. How many turns out are you running the idle screws? When you have a 4 corner idle carb you need to start 3/4 turns out as a rule of thumb. It feels okay but the exhaust is very black and I see plug fouling. The carb is a 1050 Ultra Dominator with 2 circuits, part # 0-80902HB. Install Proper Power Valve. any help would be usefull thanks. Why would you want to start out with the front carb lean, and the rear rich on the idle ?? I always do them at 1/2-3/4 turn on both to start with. Carb was fully rebuilt, specifically for my motor by a very reputable shop. From what I was told from an old desert racer, it's supposedly one of the best carbs to run on a 22r. Leaving carb where it is idle setscrew wise, pull the carb and look underneath to see how far up on the slots the throttle plates are, you are only supposed to be either just barely exposing the bottom of the slot or maybe. Once this has been done, we can move on to the carburetor. I've got a '70 Vette with a 406 in it. 5 inches of vacuum. The carb is a holley street avenger 670 and is running 68 mains and 70 secondary jets with a 6. The has a built-in restriction to the of The air bleed for the idle System ig in the main air horn. How to Install a Holley Carburetor in a Chevy 350 By Bruno Silva on Dec 04, 2009 with Comments 0 Holley carburetors are considered as the most widely used as well as recognizable high-performance carburetors available in the market. Make sure its the right size if you have one - too much air through the PCV will fight you. As soon as I start to push the gas pedal, the AFR gauge peaks out lean. The fuel that is emulsified and coming out is mixed with the air that is going by the throttle blades. The M4M is the emissions Q-Jet introduced in 1975, which has had certain adjustability added in while some of the off-idle power transition is taken out. In order to truly tune my carb, I want a better understanding of the symptoms of lean vs the symptoms of rich. Do you have a PCV valve hooked up to the carb - Mark found his to be a big source of (extra) air to the carb - air without fuel = lean. 2L Eng W/Feedback Valve-Carter Service Repl. I've attempted to solve the issue myself but I'm stuck. In order for the carbs to work properly the ignition timing and valve clearance must be correct. If you come across this problem, replace the hose with a new one. nuts out three turns (richen) Re-start, and: 3) Set balance with Uni-syn 4) Turn in one carb 1/2 turn, and listen for decrease in RPM 5) Turn the other carb in 1/2 turn, and listen for the same decrease in RPM. The popularity of the carburetor has waned in recent years. Strange as it may seem, the main jet on a Holley carb is not what you should be using to calibrate the WOT mixture delivered to the engine. Troubleshooting Your Holley Carb August 2, 2017 Wayne Scraba Fuel Delivery , How-To and Tech Tips , News 1 Holley carburetors find their way onto countless vehicles, from race cars to hot rods to delivery trucks, and for good reason: They’re the standard of performance, and without question some of the most popular and easily tunable. If you want to drop your Cruise AFR's you need to do that with the Primary jets, if this causes your WOT to go lean then you have two options, one increase the size of the power valve feed channels in the metering block or increase the jet size on the secondary side of the carb. I hope my situation is just an exception to the above quote from Holley because my engine runs so damn well as it is. Find Holley Carburetor Jets and get Free Shipping on Orders Over $99 at Summit Racing!. Dyer Blowers manufactures, sells and services 471, 671, and 871 kits for Chevy, Ford, Chrysler, Mopar, Dodge, Plymouth, Pontiac, AMC, Buick and Oldsmobile V8 Engines. Replace the float. The 7309 is the Holley list number and this is the key number if you ever rebuild it. Label all connections to the carburetor such as: fuel line, PCV vacuum and spark - distributor vacuum. 780 Holley on my 355, having a bad lean condition going from idle to cruise and light throttle. A Holley carburetor can be leaned either through the idle circuit or the main jets. Most carb builders compensate for this by closing the power valve to lean out the mixture as the vacuum increases at higher rpm. But don’t lean it out to the point where the engine begins to stumble. Is mixture screw turned in or out to lean carburetor? How do you lean idle circuit on a 650 holley? Turn the idle mixture screw in to lean the mixture, out to richen the mixture. Only the odd ball Holleys made for fuel economy work by turning in to richen. Holley carb: Lean transition from cruise to throttle. Starting at: $325. As a result, jets should never be re-drilled, nor should they be strung on a piece of wire for storage. Holley List Numbers - Holley Carburetor Identification. Make sure to increase the main jet size when installing one of these! Optimal Carburetor Setting. Move up the spike in the slider that make the fuel mixture more rich and lowering it will lean it out. Part of 1 of 1: Adjusting your carburetor. The carburetor that we would recommend is based on how the customer will drive their car and the engine package that is in the car. The carb is a 1050 Ultra Dominator with 2 circuits, part # 0-80902HB. You may need to turn them out a little, try 1. This is due to the introduction of fuel injection, which produces less emissions and more reliable results. For starters: It's a Ford Bronco with a 300 I6. The simplest possible one is essentially a large vertical air pipe above the engine cylinders with a horizontal fuel pipe joined onto one side. 7 liter with a QuadraJet 4 barrel. Jetting is 66P-73S. The carburetor that we would recommend is based on how the customer will drive their car and the engine package that is in the car. Carb Tuning 101 I thought i'd jot down a little primer on carb tuning a Quick Fuel or Holley Ultra double pumper since both have removeable air bleeds, idle feed restrictors, power valve restrictors. Install the air cleaner stud from unassembled parts. Everything is brand new and has 400 miles on it. This is a E85 high performance metering block from Quickfuel. It is really sucking down the gas. But for the enthusiast, a carb should be able to stand up to being disassembled without falling apart. If you are running an Edelbrock or Carter AFB carb, give the idle mixture screws 1/8 of a turn out (richer) and see if this helps. so i was hopeing it was running rich. It's too big of a carb for that motor so the out-of-the-box jets aren't going to be very good. Page 1 of 2 1 2 Next > If I lean them out more, the low. From what I remember, it came pretty close out of the box jet wise. 2L Eng W/Feedback Valve-Carter Service Repl. The 7309 is the Holley list number and this is the key number if you ever rebuild it. If your engine is running too rough, it's important to adjust the mixture and find the correct idling speed to decrease engine. I'm of the opinion that the Edelbrock carb is capable of delivering better power with better fuel economy than a Holley. Here's where gas mileage can really be improved! Jet the carb for an air/fuel ratio between 14. Adjust the idle using the idle mixture screws (clockwise adjustments lean the mixture, counterclockwise richens the mixture). What you are looking for is an increase or decrease in rpm. 5 inches of vacuum. 1) Replace the power valve. The main system is designed to operate and flow enough fuel either way as a 2 or 3 circuit. The engine should pick up speed and begin to smooth out. 0 intake with adapter on the 2. 1963 thunderbird, rebuilt engine and transmission. The carb has main and secondary replaceable jets with its sizing numbers on its face. The best way to set the idle mixture is to lean the carb out until the vacuum just starts to drop, then richen the mixture by about 1/4 turn. 2L Eng W/Out Feedback Valve CAN: 2280. With a warm motor and an idle around 1000rpms (see throttle stop/engine rpm adjustment) turn the idle mixture screw in until the motor starts to lose idle quality and sustainability. This screw is often. To narrow it down, tap the roll pin out of the accelerator pump lever by using a small pin punch or a small finish nail. This means checking all the hoses going to the carb and intake manifold for any cracks or loose fits. 450 cfm holley tuning/ troubleshooting 5 lbs boost, Holley 450cfm mech. Re: Which carb is better Carter bbd or holley 2280 « Reply #13 on: December 20, 2010, 13:48:40 » i like the holly 2 bbrls there easy to work on and easy to rebuild. All of Holley's models are rated in cubic feet per minute (cfm) with the smallest four-barrel rated at 390 cfm and ending with the Dominator line of racing carbs that now extends to 1,475 cfm. The reason vacuum gauges are nice during this process is its easy to find that spot where the RPM drops (vacuum level drops). So to answer the OP's question, no, leaning out the idle circuit will not lean out your cruise AFR's are 2800rpm. How can I tell if my alcohol carburetor is running lean? There are several indicators, one of which is damaged parts such as spark plugs (ground strap, porcelain areas) and pistons. However, adjusting the carburetor is a relatively simple job that can be done with a basic set of hand tools and a little bit of technical knowledge. I was however unaware of the vast adjustments that are needed in order to get maximum horsepower and torque out of the motor. Note that there are two large screws on the front of the carb, just below the nameplate. The one barrel carb on the 6 cylinder engine on my Edsel keeps backfiring unless I pull out the manual choke a little. you want it to be set so that. I currently have a edelbrock carb on my 454 chevy motor. In a CV carb, it isn't directly raised by the throttle. The best way to set the idle mixture is to lean the carb out until the vacuum just starts to drop, then richen the mixture by about 1/4 turn. An exception is some Holley carburetors. How To Adjust The Idle Mixture On Holley Carbs If this is your first visit, be sure to check out the FAQ by clicking the link above. I'm with mountian motor of the Demon carbs. I haven't checked the cats yet to see if they took them off or not the first thing I did was take off the junk holley carb because it ws trash and put on a edelbrock 600 cfm #1406 with auto choke. 050 squirter and brown cam(the biggest you can run on a 4150) and it still had a hiccup. For a typical gasoline engine, maximum power is made with a fuel to air mixture that is considerably richer (25% or more fuel) than the cruise mixture. so i was hopeing it was running rich. It has several passages that are designed to enhance performance, and a completely tunable emulation circuit, and a special power valve circuit to make for smooth transition as the carb goes from idle, on up to WOT. Tips for either Carburetor. We tend to stay around the 71 to 75 jet range. If fuel is seen dripping, the float is stuck or needle and seat are dirty and stuck. This is how I baseline a Holley 4150 Double Pumper carburetor. I'm sure 95% of everyone on here had to order theirs. As you tune the power system to open at a lower vacuum it will take more throttle opening to get the richer power mixture to kick in. thats when the power valve should be open. 3:1 (lambda 1. book and charts to lean or richen the mixture and you will not be far off. If you have an automatic transmission you will need a vacuum sec. Mercruiser GM V8 454 cid 7. The positive should go to any circuit that is hot ONLY when the engine is running. Over the past 3 weeks I have been trying to troubleshoot this problem and have not made much progress. Almost everybody has a Holley carb but not everyone know how to tune them we show you how and help you learn the science and basics of carburetors. Most carb builders compensate for this by closing the power valve to lean out the mixture as the vacuum increases at higher rpm. Move up the spike in the slider that make the fuel mixture more rich and lowering it will lean it out. 1) Turn both carbs' adj. The carb has main and secondary replaceable jets with its sizing numbers on its face. Carb was fully rebuilt, specifically for my motor by a very reputable shop. ) or the Detroit Lubricators used on 1928 and earlier Packards, and others, use a tensioned spring to control the mixture. DO NOT CONNECT THE POSITIVE LEAD TO THE DISTRIBUTOR SIDE OF THE. Holley 4000 Carburetor Kits Here are the various kits that we have for the 4000. Production carbs (like the stock RX-7 Nikki and the Holley) have the venturi cast into the body of the carb, and that venturi cannot be exchanged with a different sized venturi. Hesitation under heavy throttle: Deadspot & stumble. How to adjust holley carb srew mixture. need some advice on tuning a weiand tunnel ram with 2 new out of the box holley 600 vac. Holley points out there is a chamfer around that hole that has a strong effect on what that jet flows. From Holley, Their Sniper fuel injection, 2300 MASTER KIT, POLISHED Part # 550-849K A new intake adapter plate to go between the fuel injection and the OEM intake was made out of aluminum, but I have seen these "somewhere" already made up. 020" or so, if higher you are too rich then it goes super lean when you run out of transfer slot, think of it as mini. Almost everybody has a Holley carb but not everyone know how to tune them we show you how and help you learn the science and basics of carburetors. What you are looking for is an increase or decrease in rpm. The list of all the classic Holley carburetor numbers from the 1930s to 1980s with applications and OEM numbers as well as kits, floats, chokes and manuals is here. A carb running rich, as well as a carb running lean, can cause an off-idle stumble or hesitation upon acceleration. Selecting the Correct Carburetor. Holley Street HP carb too rich at idle. At the Max of 7000 RPM the vacuum was 0". The info that Gert sent in contains info on how to adjust holley floats, a high float level will cause a rich condition and low level will lean it out. If the above adjustments did not get the engine running properly, the jets will need to be changed. runs hot! after a mechanic worked on it and replaced the carburetor, 20 Answers. I have an issue I have been hoping to resolve through searching and lurking, but to no avail. Holley does a pretty decent job of supplying a ready-to-run carb, so the jetting, pump cam, shooter sizing, and spring rates are usually pretty close. Increasing the size of the intermediate bleed will lean out that circuit. If you come across this problem, replace the hose with a new one. I have a 3310 on my 406 and have been tinkering with it now for over a week. Generally, Holley over fuel carbs via PVCR to ensure that they don't ever run lean in the engines selections. A cold engine is always stumbly. All carburetors get completely disassembled and boiled out. 2 wiht the carter carb and it is running way to rich. Check the body for cracks around inlets. My holley carb wont stop cutting out? how do i adjust my air mixture screws. It allows fuel into the carburetor until the carburetor bowl is full, then shuts off the fuel flow. do you guys know what kind of jetsetting i have to put in, my guess is that (after reading a lot about Holley's ) the jets are not right. The accelerator pump squirts gas like a squirt gun every time you push down on the gas pedal. 1) Turn both carbs' adj. fuel pressure. Note: a lean condition is not the only possible source of this type of problem. 5 inches of vacuum instead of 8. Adjust the idle using the idle mixture screws (clockwise adjustments lean the mixture, counterclockwise richens the mixture). For a street engine, one way to lean the part-throttle air-fuel ratio and improve throttle response would be to reduce the primary jet size slightly (assuming the primary circuit is a bit rich). The motor is a FRPP 302 crate with supposedly a "mild" cam and edelbrock rpm air gap intake, hooked to an AOD trans. Lots of folks lately with Holley issues. The carb has main and secondary replaceable jets with its sizing numbers on its face. Otherwise, air will flow across the top of the carb and out of the inlet tract rather than into the air horn. I ended up with a 50cc pump and. You may have to register before you can post: click the register link above to proceed. the motor makes around 11 to 1 compression and runs great with a 950 cfm dbl pumper on the track. A carb running rich, as well as a carb running lean, can cause an off-idle stumble or hesitation upon acceleration. the 1st carb i ever rebuilt was a holly 2 bbrl. on most carbs like holley full manifold vacuum will usually be on the base plate. Install the air cleaner stud from unassembled parts. recently bought a 2nd hand 6210 holley double pumper. It is a very common carb for IH vehicles. Start the engine and turn one of the idle screws in or out. Find helpful customer reviews and review ratings for Holley 0-80770 Street Avenger 770 CFM Square Bore 4-Barrel Vacuum Secondary Electric Choke Carburetor at Amazon. 100 Percent Wet Flow Tested By Holley Technicians. Just had to add some fuel with the accelerator pump squirter and cam. Plugging the bowl vent forces fuel into the engine by way of the PV vacuum passage; if the PV is good,. My holley carb wont stop cutting out? how do i adjust my air mixture screws. You could hurt it if your really getting on it when its jetted to lean at the lower elveations. adjust the secondary "idle speed" screw about another 3/8 of a turn more. Mine was about one and an eigth open. The main system is designed to operate and flow enough fuel either way as a 2 or 3 circuit. So with the carb I ordered Holley P/N GA4708 which is the tuning kit; this is actually the kit for the 625 cfm carbs but that's fine for me because I needed to lean mine out from stock. A rough check on Bing carbs shows there are at least 13,860,000 different combinations of jets. The old Holley Carburetors book by Ulrich from 1972 has a several pages of information that I could scan for you if you send me a PM with an e-mail address to send the files to as PDFs. In some instances this can cause the machine to "bog" as if it were actually running out of gas. Above about 70 mph, the power valve cuts in. 670 inch solid roller cam, patriot 225 runner cnc ported heads, everything else forged. So the 670cfm HP or Avenger Holley, when dry flowed, will flow over 750. lynn bignall is the owner, he would be glad to talk to you and help, he is greatnumber is 715 835 3726. The jets are located in the bottom of the carb. tromp on it hard and it will lean back fire out the top of the carb on these carbs try to read the instructions up front there are a few measurements you want to know about first the metering rod assembly is adjustable under this aluminum plug so it is important when you get it out to measure it. the motor makes around 11 to 1 compression and runs great with a 950 cfm dbl pumper on the track. out and installed just a regular electric pump straight to the filter to the Carb. BG tech advised to drill out the air bleeds, then came back and said they wouldn't put that carb on a 347. Now watch out for a loose needle adjustment. VW Carburetor Jetting Procedure. Ford Small-Block Engine Interchange: Induction System All 221, 260, 289, 302, 351W, and 351C 2-barrel engines were originally fitted with dual-plane iron intake manifolds and the venerable Autolite 2100-series 2-barrel carburetor from the factory. Write Your Own Review You're reviewing: Holley 0-4774C 650cfm 4150 Carburetor. My carb leaks fuel out of the overflow hose at the bottom of my carb My carburetor leaks fuel when I turn the fuel on at a consistent leak out of the bottom hose of the carb. When I give a very light throttle input, with on take off or while cruising, I have a lean spot (verifyed with an O2 meter) hich is causign the car to stutter for a second or too. Jets aren't the only components to consider when it comes to richening the fuel circuits in your Holley carburetor. 2 wiht the carter carb and it is running way to rich. Before you go trying to fix all the errors of the previous carb tuner, set your carb up to the stock Holley spec for your carb List Number (stamped into the front of the air horn). And they run miserably when you try to lean them out. I'm of the opinion that the Edelbrock carb is capable of delivering better power with better fuel economy than a Holley. Discussion in 'Technical' started by scooper77515, Feb 24, 2012. Make sure its the right size if you have one - too much air through the PCV will fight you. How to Fix Engine Backfires Does your engine back fire and you are wondering why? We are a group of ASE certified mechanics that have created this guide to help you save money by fixing your car yourself or to see what you are paying for when taking it in for repairs. Again it is vital that both screws have the same number of turns. Actually with the PV blocked you cant tune your carb for maximum performance, you will either be to fat on bottom end or to lean on top end. Holley carb: Lean transition from cruise to throttle. Hi all, Doing some tuning work on my Holley 390 and was looking for some advice. Your carburetor is a crucial part of your engine, and without a working carburetor, you won't be driving anywhere. However, adjusting the carburetor is a relatively simple job that can be done with a basic set of hand tools and a little bit of technical knowledge. Turning this screw clockwise will reduce the amount of air entering the carburetor, and will, therefore, richen the mixture (refer to a shop manual for correct settings). i don't know if you have solved your carb prob yet or not, but if not, we have a great sponsor-Bigs Performance Carbs, from altoona, wisconsin, we used a 4412 that they sponsored to us last year on our street stock, and never had one prob with it at all. Occasionally, the adjustment screws on a Holley carburetor will loosen from engine vibration while it is running, causing the motor to run poorly and reducing your fuel mileage. It is really sucking down the gas. WOT - Anything over about half throttle reduces manifold vacuum to a point where the power valve should open. The negative lead should go to any good engine ground. However, if you see black soot then you're running rich - meaning you've got too much fuel - if you see white residue then you've got too much air flowing in or you're running lean. If engine speed increases with that one screw, adjust all of the others to match. Holley points out there is a chamfer around that hole that has a strong effect on what that jet flows. probably not cheap but holley makes an off road carb already set up and someone makes a kit for those. How to Tune a Holley (basic) by Lars Grimsrud SVE Automotive Restoration Musclecar, Collector & Exotic Auto Repair & Restoration Broomfield, CO Rev. That job is the function of the power valve and the PVRC. If that doesn't work then consider going to a richer main jet. On Holley carbs, there are two screws that control the idle mixture on the primary metering block. As a starting point, set the needles 1 1/2 turns out from the full lean position, and then adjust for best idle. Once this has been done, we can move on to the carburetor. The carb has main and secondary replaceable jets with its sizing numbers on its face. It will probably not heat up enough again until you are beaten by the car in the other lane. In addition to throttle plates, the lower portion of a carburetor contains numerous air. If your engine is running too rough, it's important to adjust the mixture and find the correct idling speed to decrease engine. Learn how to select, install, tune and modify all popular Holley performance carburetors. Carb manufacturers already know how much fuel a carb flows, and the factory setup is fine for 99 percent of motors out there. he said the carburetor was bad, got another one from thund. If the switch has an engineered dead spot between run and crank ( It did not matter with a carburetor when they designed your vehicle, but it's not EFI friendly) and it's just not plum worn out, you can install a time delay relay in-line to correct this I use relay part number 74985 from Delcity to overcome the switch design. Once this has been done, we can move on to the carburetor. need some advice on tuning a weiand tunnel ram with 2 new out of the box holley 600 vac. How to Adjust a Holley Carb - Adjusting a Holley carburetor is a job that can be done in just a few minutes. Before you go trying to fix all the errors of the previous carb tuner, set your carb up to the stock Holley spec for your carb List Number (stamped into the front of the air horn). You may have to register before you can post: click the register link above to proceed. It allows fuel into the carburetor until the carburetor bowl is full, then shuts off the fuel flow. As it is, it's going to have a weaker signal than Holley designed it to have at low rpms. The best way to set the idle mixture is to lean the carb out until the vacuum just starts to drop, and then richen the mixture by about 1/4 turn. This is the Demon carb. it has a comp cam do not know what size. Typically a carb backfire means too lean a mixture, or timing is too advanced. In most cases, it will be unnecessary to increase jet size more than four numbers greater than the out of the box setting. But for the enthusiast, a carb should be able to stand up to being disassembled without falling apart. That would be correct if the engine was running ENTIRELY on what came out of the idle discharge holes. For example List 4053, or List 4777-4.