How To Lean Out A Holley Carb


When the vehicle is cruising down the highway the mixture needs to lean out considerably if good mileage is to be achieved. I'm with mountian motor of the Demon carbs. A Holley carburetor can be leaned either through the idle circuit or the main jets. I would Go with the holley IMO, the 600cfm if your friend knows how to rebuild carbs easily, if he doesnt, buy the 570 for the 100 or so extra, and it should work basically out of the box with some. Leaning Holley carb midrange I have a great idle AFR and "good" high RPM AFR. Carbs with removable high-speed air bleeds invite calibration problems initiated by the unwit­ting tuner. See our Performance Carburetors, Intake Manifolds, Cylinder Heads, Crate Engines, Electronic Fuel Injection. On a Holley carb, check float levels too. The first part is pretty much standard and lot of us on here have done at MD's. Brodix BB2 heads and 4500 intake with an adapter for a 4150 carb MSD dizzy and 6AL box!. This is how I baseline a Holley 4150 Double Pumper carburetor. 2 wiht the carter carb and it is running way to rich. Hi all, Doing some tuning work on my Holley 390 and was looking for some advice. What you are looking for is an increase or decrease in rpm. on most carbs like holley full manifold vacuum will usually be on the base plate. The problem is it constantly loads up and will hardly idle. As a starting point, set the needles 1 1/2 turns out from the full lean position, and then adjust for best idle. Holley carbs come with a standard shooter size which differs by carb list #. Mercruiser GM V8 454 cid 7. 2 wiht the carter carb and it is running way to rich. Move up the spike in the slider that make the fuel mixture more rich and lowering it will lean it out. 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. I have place a post related to touble I get with heavy smoking engine and stuffing at idle and slow speed. some engine details. 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. Most carb builders compensate for this by closing the power valve to lean out the mixture as the vacuum increases at higher rpm. You might check to see if your float is adjusted right, it could be flooding the carb, and running too much gas out of it. Example of a carburetor with a FUEL SCREW, this is what the pilot jet feeds Watch a step by step tutorial on how to adjust the idle mixture screw on a typical carburetor. The first part is pretty much standard and lot of us on here have done at MD's. Please explain what you mean by rich and throwing fuel out? The hesitation, is it a bog (lean) or rich (sputter)? List all mods and what your current temp and altitude are. If you are going to change carbs you'd better be prepared to spend some time and money on the job. Note: a lean condition is not the only possible source of this type of problem. 010 larger at a time until the mixture screws are required to be at 2 turns out as a baseline. I know the smog pump is unhooked so we have to see what happens there. Bolting the carb back up is simply the reverse of disassembly. Could someone tell me how to lean it out. In order to check for the proper jetting at the main jets, new spark. Everything is brand new and has 400 miles on it. The difference was an idle vacuum of about 4 to 5 inches for the race cam and 11 to 12 inches for the street cam. Is there a simple screw adjustment to lean the carb out a little without screwing something up?. The Holley Truck Avenger is one of the worst carbs to try to run with economy in mind. This information-packed guide provides a detailed view of basic carburetor functioning, modifying for performance applications, custom-tuning for street, racing, off-road, turbocharging, economy, and other special uses. If your carbs are clean (I mean REALLY), all your vacuum hoses are good, your air-cut off valve fresh, choke linkage free, butterfly pivots not worn out, floats set and operating correctly, vacuum pistons free, air and fuel filters fresh and you’ve synchronized AFTER all other tune-up issues are perfect, you should have excellent results. The boosters in a Carter design (Edelbrock) tend to be more responsive than the Holleys on the street type carbs, and Holley's approach to that is to add more fuel both thru the acelerator pump(s) and the power valve circuit. The float bowl mounts on the front of the carburetor and can be metal, or glass. The simplest possible one is essentially a large vertical air pipe above the engine cylinders with a horizontal fuel pipe joined onto one side. Holley carburetors come with a standard shooter size, which varies by the carb list #. Selecting the Correct Carburetor. We carry Carburetors for: American cars and trucks, Import cars and trucks, Antique cars, classic cars, muscle cars, boats, and Industrial Engines. HGM's AccuLink is a really slick chrome steel conversion package that provides a GM-style TPS sensor to all in style Holley, Q-Jet, and Edelbrock carbs. A typical Holley carburetor has two screw-in jets that meter the amount of fuel that flows to each primary venturi. Follow the Edel. I have attempted adjusting the pilot screw, which did alleviate the popping symptoms and gave me a much smoother ride at 25 mph. The fuel that is emulsified and coming out is mixed with the air that is going by the throttle blades. The bog or hesitation may be caused by a momentary lean condition when the carb goes from the idle throttle postion to the main metering system. 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. Page 1 of 2 1 2 Next > If I lean them out more, the low. Stock carb. DISASSEMBLY The following procedure for disassembly will separate the. lynn bignall is the owner, he would be glad to talk to you and help, he is greatnumber is 715 835 3726. With your car in gear and your foot on the brake check your manifold vacuum, whatever your reading is subtract two and thats the size PV you should start with. Needle: The needle is attached to the carb slide and is raised and lowered when you push and release the throttle. As soon as I start to push the gas pedal, the AFR gauge peaks out lean. s for that carb. In order to check for the proper jetting at the main jets, new spark. See our vacuum ports. Using Holley's Carb tuning DVD will eliminate the possibility of missing a step. Take tank and top center air box off. If you are experiencing a bog or hesitation off idle, you can try a larger, higher # shooter size. 4) No power or heat source to choke. Then, tweak the front carb for the highest and steadiest vac reading. If you notice these symptoms, tune your Demon carb in your garage for improved engine performance. 04) in all cases. the plugs are white and have even burnt the tip off a few times. Begin the final needle valve adjustment with the boat running at a slow speed. 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. This is how I baseline a Holley 4150 Double Pumper carburetor. NOTE: Holley carbs also have a secondary idle speed screw, and it should be adjusted in a similar fashion. Let us know how that goes, and we'll continue the virtual tune up then. Holley Carb Baselining/Tuning It's been a while since I've been asked a carburetor-related question, but this one came up this week so I figured I'd do a little writeup. 2L Service Carburetor Manual cause an holley 2280 carburetor to flood to more lean; how to adjust carburetor on 82. I am gitting ready to put a motorcrfat 2150 carb on but i need to passs emisions now wiht the carter carb on. Turning them in will restrict the flow of fuel to the idle circuit and lean the mixture. Small details can get overlooked or forgotten. I'd go 750 vacuum secondary, especially with the automatic trans. it may not be possible to economically recalibrate the carburetor! The key is the style of carburetor. Holley's are an easy carb to tune in my humble opinion. 450 cfm holley tuning/ troubleshooting 5 lbs boost, Holley 450cfm mech. SU carb leaning out and the starving - posted in Engine: I have a 179 with a 3. 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. I used a Holley spreadbore that was designed specifically to replace the Thermoquad that came on these cars. 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. Install the air cleaner stud from unassembled parts. Holley type carbs come with a standard shooter size which differs by carb list #. This is an easy one. The carb has main and secondary replaceable jets with its sizing numbers on its face. In order to truly tune my carb, I want a better understanding of the symptoms of lean vs the symptoms of rich. Played with it some and decided that 500 CFM was just way to big. Adjust the idle using the idle mixture screws (clockwise adjustments lean the mixture, counterclockwise richens the mixture). To locate and identify your Holley carburetor the number is located stamped into the front of the choke tower and will either start with the letter R followed by 4 or 5 digits. Turbo Carb - Blow Through 101 if you're going for a Holley, a 600DP is a huge carb to run on the 6 on the street, particularly if you have to pass emissions. Metering rod equipped carbs can also have the primary rods changed at this point to either lean (thicker rod) or richen out the primary bores. Which way do I turn the mixture screw to lean out the carb. 4) Venting system problem. On a Holley carburetor, the needle and seat are on the top of each float bowl and can be removed and cleaned. With your car in gear and your foot on the brake check your manifold vacuum, whatever your reading is subtract two and thats the size PV you should start with. I have had a look around other forums and seen a bewildering array of stuff that has confused me. Once the engine's idle speed has begun to slow, back each idle mixture screw out 90 degrees to complete the process. Of course, if you convert to a square bore (either by manifold swap or an adapter) you have a much greater carb choice. This may occur with: 1) a wide open throttle to provide more power; 2) high engine load; 3) high engine rpm where the air-fuel mixture tends to lean out; or 4) engine over heating. Leaning out a carburetor will increase the fuel economy and possibly increase the power to a certain point. From what I was told from an old desert racer, it's supposedly one of the best carbs to run on a 22r. First carb was an out of the box holley 750 vac. Use the screwdriver and turn the needle valve screw clockwise 1/8 turn to lean the fuel mixture. When replacing these early carbs, it is proper to use the later model with the pressed in pilot jet bush. If the carburetor is adjusted to make it work well at high speeds, it will be too lean at low speeds. In order to check for the proper jetting at the main jets, new spark. This article shows you how to adjust the air fuel mixture and the idle air speed - the two most common adjustments made when tuning a carburetor. I cant get the damn thing to lean out. Brodix BB2 heads and 4500 intake with an adapter for a 4150 carb MSD dizzy and 6AL box!. 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. Unfollow dodge 318 holley carburetor to stop getting updates on your eBay Feed. Holley carbs come with a standard shooter size which differs by carb list#. I tested this attaching a vacuum gauge to them and running a boat up through the RPMs to see. After you get the primary side dialed in, bring the secondary back into play. Popping out the exhaust could be most anything, but if you're way too rich that can happen as well. idle air screws, used to lean out or rich fuel air mix. Operate the carburetor throttle lever by hand to assure the correct travel (no sticking or binding) by opening to wide open throttle and. I adjusted the electric choke dial towards lean, thinking it's too rich on startup but that doesn't seem to make a difference. ? should lean it out. The Holley 650 (P/N: 0-4777-9) carb is factory jetted on the primary side with 67 main jets and a power valve with a. These restrictions determine the amount of fuel enrichment the power valve circuit provides at wide open throttle or when the engine load is sufficient to reduce the manifold vacuum below the rated value of the power valve. Dropping the jetting it made a tiny bit more power, but it starts to get a little lean on the top end without fully get rid of the dip in the middle. Before you decide to rebuild a carb, make sure it’s still usable. Backfiring through the carb can be an indication of being too lean - this is not a good thing for your blower build. 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. 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. Mine was about one and an eigth open. going to the mechanical pump to the fuel filter to the Carb but I took both of. The bog or hesitation may be caused by a momentary lean condition when the carb goes from the idle throttle postion to the main metering system. But don't lean it out to the point where the engine begins to stumble. I temporarily replaced the Edelbrock with a known-good Holley off a different 351C 4V and it ran great. Turning the idle mixture screws on the side of the metering block, out,counterclokwise,will richen the mixture. But it doesnt. We put a holey carb on but the air cleaner and shaker would not fit right and he bolted the shaker to the hood. The main system is designed to operate and flow enough fuel either way as a 2 or 3 circuit. Model T Carburetor - Page 1 of 18 Sort: [Please Select A Sort Order] Item Popularity Newest Items First Item Number (0-9 A-Z) Item Number Descending (Z-A 9-0) Lowest Price First Highest Price First Description (0-9 A-Z) Description Descending (Z-A 9-0) - Per Page: 10 Items 20 Items 30 Items 40 Items 50 Items 100 Items. so gauge connect [ $10. Now watch out for a loose needle adjustment. Short answer, lean burn models used a Holley 6145 carb, non lean burn used the Holley 1945. So if a smart tuner was to slightly lean out the idle-feed restrictor in the carburetor, this would make the engine run lean at part throttle. it has a comp cam do not know what size. Idle problems can result if these passages become obstructed or the base gasket used with the carb allows air leaks. Adjust the idle using the idle mixture screws (clockwise adjustments lean the mixture, counterclockwise richens the mixture). Holley mechanical and electric fuel pumps are designed to deliver the pressure and volume needed for performance use. I would Go with the holley IMO, the 600cfm if your friend knows how to rebuild carbs easily, if he doesnt, buy the 570 for the 100 or so extra, and it should work basically out of the box with some. I decided to try this Holley and it's awesome! Looks great on my '65 Falcon with a 351W stroker motor (389ci). thanks in advance. Should you rebuild a carburetor or replace it? When people figure out their carburetor is causing problems they might think they only have two choices. Could someone tell me how to lean it out. I had to turn it down some to get it to idle. 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. So this motor and carb ran good for 3K miles then started doing this? Important to know in order to figure whether it is a set-up problem or a failure problem. You set the fuel level, with pump running (wrap a rag around the carb so gas doesn't leak onto the manifold!!!) so the fuel is just starting to dip out of the "peep-hole" in the side of the float. Leaning out a carburetor will increase the fuel economy and possibly increase the power to a certain point. On these carbs, the idle discharge circuit supplies the fuel from idle to about 25 mph. I adjusted the electric choke dial towards lean, thinking it's too rich on startup but that doesn't seem to make a difference. Dropping the jetting it made a tiny bit more power, but it starts to get a little lean on the top end without fully get rid of the dip in the middle. make sure your on flat ground made that mistake once. Then turn the adjustment about 3/4 turns counter-clockwise and start there. Turning them out only makes the rich idle condition worse. If you take fuel line off at center rear of carbs and spray full, this will effectively place cleaner in all your carbs. The administrator has banned your IP address. If you have a bit of a stumble in very light, low speed operation, sometimes it helps to richen it up by another 1/4 turn. The main body includes the metering block, float and the economizer. There are subtle differences in the kits, so be sure to use the carburetor number and match to the list contained in each carburetor kit. the plugs are white and have even burnt the tip off a few times. If you strip out the bowl's threads on an older carb, you'll beat hell finding a replacement. The administrator has banned your IP address. 1) Replace the power valve. Attach the throttle plate to the shaft with the screws so that the numbers on the throttle plate face the idle mixture screw and the dimples face in. Hesitation when I would get on it (seemed like a lean condition)everytime and very week topend. I have the holley 4150 hp 830 cfm annular booster carb on my 408 sbc. When the carburetor sits squarely, it is safe to install nuts and washers. My buddy here on the forum runs lean with 6 jet sizes bigger than my 750 double pumper holley. In order to check for the proper jetting at the main jets, new spark. Holley carbs come with a standard shooter size which differs by carb list#. Leaning Holley carb midrange I have a great idle AFR and "good" high RPM AFR. make sure your on flat ground made that mistake once. Then, he could use the ECI to supply the additional fuel required, so the engine would be operating with a feedback system as it runs down the highway – much like an EFI system. 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. White or light grey muffler end pipes. I'm with mountian motor of the Demon carbs. If no changes have been made to the bike, and it previously ran well, a lean mixture can be traced to a leaking inlet manifold or leaking exhaust (often at the interface of. The 5200 carb flowed 117 cfm including air filter, the 350 flowed 119. A lean pilot jet setting will cause your engine to surge at very low RPM’s, bog or cut-out when the throttle is opened quickly and have trouble idling down. It just gets leaner and leaner and the engine audibly strains and struggles until the powervalve kicks in and when WOOSH, 11. These restrictions determine the amount of fuel enrichment the power valve circuit provides at wide open throttle or when the engine load is sufficient to reduce the manifold vacuum below the rated value of the power valve. Could someone tell me how to lean it out. I currently have a edelbrock carb on my 454 chevy motor. A cold engine is always stumbly. Everything is brand new and has 400 miles on it. Short answer - a carb can't give you a horsepower increase. Whether you have a CCS Performance or a stock HOLLEY® carburetor (or a flow-modified CCS model), jetting should be fairly close if the carburetor is used in the intended application. I forgot to mention the main problem with q- jets is they run lean really lean. But it doesnt. I am a firm believer in that there is no such thing as a carburetor that's too big (CFM rating), BUT usually most carbs that are "big" are also designed for big cam, big inch, and big horsepower V8s. 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. I cleaned out all the passages including the idle bleeds and passages and they are all clear. The Ford book reccomends 2 1/2 turns rich then lean it out. If used, these early BSA & Triumph carbs should also have 622/235 update kit installed. Keep in mind there are other factors that could make her run rich. Carburetor Troubleshooting Guide. I set the screws on my metering block to 1 3/4 turns out after a rebuild and it start good warm or cold so I stopped screwing with them. 5:1 compression. This is to compensate for that first burst of air when you open the throttle. Stock carb. Holley offers likely the widest assortment of sizes of any of the carburetor companies on the market. Here’s where gas mileage can really be improved! Jet the carb for an air/fuel ratio between 14. An exception is some Holley carburetors. 04) in all cases. 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. If that doesn't work then consider going to a richer main jet. Follow the Edel. If air is forced past the carburetor it can siphon fuel, causing the engine to run lean. A Holley carburetor can be leaned either through the idle circuit or the main jets. Discussion in 'Technical' started by scooper77515, Feb 24, 2012. Carburetor Set Up and Lean Best Idle Adjustment If the carb is out of the warranty period and no defect is determined we will estimate the possible cost of tech. adjust the secondary "idle speed" screw about another 3/8 of a turn more. You may can contact Holley any way, and get the information with out knowing the numbers. You may need to turn them out a little, try 1. New 3-14-01 This tech paper will discuss basic set-up and tuning of Holley vacuum secondary carbs for optimum street performance and drivability. In addition to throttle plates, the lower portion of a carburetor contains numerous air passages. 670 inch solid roller cam, patriot 225 runner cnc ported heads, everything else forged. Stock carb. 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. Follow the Edel. The main system is designed to operate and flow enough fuel either way as a 2 or 3 circuit. Mine was about one and an eigth open. The only effect of the idle mix screws it to strarve the engine when screwed all the way in- it doesn't help to screw screw them out (richer). im not a holley fan so i didnt keep track but help is out there good luck. Here’s where gas mileage can really be improved! Jet the carb for an air/fuel ratio between 14. Drill the idle air bleeds out (located in the outer four corners). Could someone tell me how to lean it out. Run the boat at high speed and repeat the procedure if necessary until the carburetor is adjusted for high speeds. 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. Holley additionally has a package for Gen three Dominator carbs that could be very compact and bolts on to the bottom plate. 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. This is even after changing the truck rods out of the carb. My Holley cfm seems to be running a bit rich. The big four suppliers of 4 barrel carburetors today are Edelbrock, Holley, Quick Fuel and Barry Grant, each of these carburetor designs have strong and weak spots. Drill the idle air bleeds out (located in the outer four corners). You may find one on eBay or Craig's List. 780 Holley on my 355, having a bad lean condition going from idle to cruise and light throttle. The level of fuel in the carburetor bowl is critical: too low and the carb will run lean, too high and it will run rich. These restrictions determine the amount of fuel enrichment the power valve circuit provides at wide open throttle or when the engine load is sufficient to reduce the manifold vacuum below the rated value of the power valve. Back out ½ turn more, or until the screw does nothing or runs worse then turn back to the point where it ran its best. Reset idle mixture screw. it backfires real bad (and fast) when driven, hopefully i havn't broken anything yet. Only the odd ball Holleys made for fuel economy work by turning in to richen. Make these adjustments ¼ turn at a time. Carburetor Set Up and Lean Best Idle Adjustment If the carb is out of the warranty period and no defect is determined we will estimate the possible cost of tech. The Holley Truck Avenger is one of the worst carbs to try to run with economy in mind. Which nut to turn to adjust for a leaner fuel mixture on a 600 4160 holley carb?. First, turn in the mixture screw until the engine dies or runs worse, then back out the screw (recommend turning ¼ to ½ turn at a time). If you have a bit of a stumble in very light, low speed operation, sometimes it helps to richen it up by another 1/4 turn. In this article we're going to talk about a third possibility that few realize is an option. The one barrel carb on the 6 cylinder engine on my Edsel keeps backfiring unless I pull out the manual choke a little. Plugging the bowl vent forces fuel into the engine by way of the PV vacuum passage; if the PV is good,. I've never had much trouble getting them to do what I wanted them to do. Holley’s kit is simple to install, using a standard TPS sensor adapted to follow the primary throttle linkage movement, but this kit does require a carburetor using an electric choke. i have set timing 12 to 14 deg adv. The carb has main and secondary replaceable jets with its sizing numbers on its face. it backfires real bad (and fast) when driven, hopefully i havn't broken anything yet. You might check to see if your float is adjusted right, it could be flooding the carb, and running too much gas out of it. The problem here is possibly the intake manifold and TBI adapter, with the manifold being designed for a four-barrel carb it may just not distribute fuel as well with the two barrel sitting on the adapter in the middle of the carb flange. 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. Page 1 of 2 1 2 Next > If I lean them out more, the low. At first I thought maybe the Demon boosters do not draw as much fuel because of less air flow. Crank engine (ignition "off") with air horn removed to fill float chamber. The only effect of the idle mix screws it to strarve the engine when screwed all the way in- it doesn't help to screw screw them out (richer). carburetor is to move fuel out of the. in carburetor distribution so that the carburetors should not be changed from one system to another. It will vibrate out of adjustment if your needle valve clamp nut is not tight enough. Leaning Holley carb midrange I have a great idle AFR and “good” high RPM AFR. ? should lean it out. My only experience is with Holley and Demon carbs, so I ordered a new Holley Street HP last night. Leaning Holley carb midrange I have a great idle AFR and “good” high RPM AFR. Adjustment should be made in slow, small increments. 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. Turning the screw out makes the idle mix-ture more rich. Of course, if you convert to a square bore (either by manifold swap or an adapter) you have a much greater carb choice. If you're determined to use that 750 Holley, you can still get it to run very nicely with some. Hold off on the radical diagnosis until you check it out at 180 or "normal" operating temperature. The main system is designed to operate and flow enough fuel either way as a 2 or 3 circuit. So to answer the OP's question, no, leaning out the idle circuit will not lean out your cruise AFR's are 2800rpm. Any further in and it will stall or hesitate at the snap of the throttle. and they run great. i have set timing 12 to 14 deg adv. but the old setting was pretty close to my new one. #10 Weird Sounds. 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. See if that clears it up. The Holley 650 (P/N: 0-4777-9) carb is factory jetted on the primary side with 67 main jets and a power valve with a. Another approach to figuring out why the carb isnt working right would be to reverse the steps normally used in tuning. If it is at idle adjust the ilde mixture screws and go from there. 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. If you are experiencing a bog or hesitation off idle, you can try a larger, higher # shooter size. Only the odd ball Holleys made for fuel economy work by turning in to richen. 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. Female: Holley offers a variety of universal performance carburetors. How to tell what size carb you need: You take the engine cubic inch and multiply by the maximum RPM and divide by 3456. Made it so that the boat flat out would not run at anything other than WOT, couldn't idle. It also gives gas while the carb switches from the idle circuit to the main circuit. FYI- Every Holley carb I've ever "cured" of the flat-spot was way out of proper adjustment or was mis-timed. 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. On these carbs, the idle mixture screws not only impact the idle circuit but also the first 1/8 throttle. 010 larger at a time until the mixture screws are required to be at 2 turns out as a baseline. The float bowl mounts on the front of the carburetor and can be metal, or glass. FYI- Every Holley carb I've ever "cured" of the flat-spot was way out of proper adjustment or was mis-timed. Too big a carb can also be your problem. That was to be sure that they didn't lean out. Which way do I turn the mixture screw to lean out the carb. Back out ½ turn more, or until the screw does nothing or runs worse then turn back to the point where it ran its best. Just remember that too much of a good thing can get you into trouble - before fine tuning a carburetor you should take note of the stock specs so you can always come back to where you started. type carbs employ a “reverse idle” system in which adjusting screws have to be turned counter-clockwise to lean the mixture. The article also shows the Offy plus 390 Holley 4 bbl. Out of the box, their jetting is extremely close for most applications, provided you've selected the correct CFM carburetor for your application. The secondary side of this carb does not use a power valve to balance the fuel flow between the primary and secondary, so it uses 6-step larger 73 jets. Since 1938, Edelbrock has manufactured its core products in the USA for quality & performance. First, turn in the mixture screw until the engine dies or runs worse, then back out the screw (recommend turning ¼ to ½ turn at a time). It is really sucking down the gas. was the best we have ever had. You set the fuel level, with pump running (wrap a rag around the carb so gas doesn't leak onto the manifold!!!) so the fuel is just starting to dip out of the "peep-hole" in the side of the float. carburetor is to move fuel out of the. 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 the mixture is too lean, there is a dead spot at this instant, no gas. When removing the fuel line, slide a rubber cap plug over the end to prevent fuel from running out, which may create a fire hazard. Hesitation when I would get on it (seemed like a lean condition)everytime and very week topend. I have a holley carb for my correct craft of 1900 Ford PCM engine. Holley's are an easy carb to tune in my humble opinion. On top of that, the price of fuel made the swap an attractive "de-modification". On Holley carbs, there are two screws that control the idle mixture on the primary metering block. The reason vacuum gauges are nice during this process is its easy to find that spot where the RPM drops (vacuum level drops). 050 squirter and brown cam(the biggest you can run on a 4150) and it still had a hiccup. Holley Carb Baselining/Tuning It's been a while since I've been asked a carburetor-related question, but this one came up this week so I figured I'd do a little writeup. If you are experiencing a bog or hesitation off idle, you can try a larger, higher # shooter size. There are subtle differences in the kits, so be sure to use the carburetor number and match to the list contained in each carburetor kit. It just gets leaner and leaner and the engine audibly strains and struggles until the powervalve kicks in and when WOOSH, 11. A Holley carburetor can be leaned either through the idle circuit or the main jets. A simple jet carburetor cannot maintain the needed air/fuel ratio under varying suction levels and becomes too rich at high suction levels. 050 solid roller cam, 10.