Quick Fuel Carb Stumbles Off Idle

To cure this condition, either slightly undo all four idle-mixture adjusting screws to enrich the system or enlarge the idle-feed restrictors in the metering blocks. If you stomp it, it takes off just fine but the car lights the tire when you give it to much gas to get going. Further, with eight venturi bores aligned with their corresponding intake runners, these Demon Inline Twins offer excellent fuel distribution and atomization. When a float needle becomes damaged, it will usually begin to leak a small stream of excess fuel into the carb throat at idle speeds, and during throttle release from high rpms. My engine builder sold me the carb still in the box. the idle to main transition was horrible with this body before,and the main circuit was lean as well due to the big bleeds. Terms often used are: Stuttering Hesitating Running Rough etc etc. Hopefully you'll see a little tube, covered by a rubber plug. The engine vibration causes the needle valve to leak, which causes the engine to run even rougher. I went to the 48 idle jet and raised the needle 1 washer and am running a 195 main with 95" and cams and exhaust. If I let it idle for a bit, it seems to sort of "settle in" to idling. Low fuel delivery. This carb seems to run great in all areas except right off of idle and if you get into the throttle a little bit at low RPM in 4th gear. My motor leans out under quick acceleration and I've tried all holly accelerator cams to adjust the pump to get more fuel out of the pump. I modified the carb for this build. This test is being done while the carburetor is on the engine. Normally do not turn the pilot screw out more than 2. Most of the carburetors need to be re jetted to some extent when dealing with a modified engine. QFi Key Features: Designed for street and off-road vehicles, trucks, RV’s, muscle cars, and more. As rule of thumb, set your fuel pressure to these ranges based on the carburetor brand: 5-7 psi for Holley, Quick Fuel, AED, Willy’s, or Summit Racing; or 4-5 psi for Edelbrock or Jet. #110 or #115 idle air jet (external – in the brass elbow) This should be modified to fix the infamous “off idle” glitch. If you attempt to accelerate too hard off idle, to the point where the secondaries kick in, the car bogs and stumbles to the point where it dies unless you lift your foot off the pedal. If it does you can then go back to dialing in the IAB. The problem I had was with my 1990 NA, which had mysteriously developed a deep hesitation whenever the car moved off from rest. Adjusted by the idle adjust screw on the lower right side of the carb when viewed from the drivers side. If the idle speed increased, adjust the idle speed knob to return the bike to a real slow idle speed. Carb can get bumped in shipping or transportation and can accidentally change the setting. Just a mile up the road and back. Fill bowl with gas. When it is idling the engine runs fine without any miss or hesitation. From idle, if you just tweak on a little throttle as you ease out the clutch, it almost stalls for a second until. I had a little trouble getting a signal to my MSD box to fire the coil during cranking. A carburetor not built for a specific engine and fuel should supply an air/fuel mixture rich enough for a variety of engines since engine damage could result if the carburetor is too lean. 3) Clogged idle mixture circuit. If I stop completely for a second or two, there is no hesitation. A race carburetor isn’t designed to be efficient at lower rpms. A typical Holley carburetor has two screw-in jets that meter the amount of fuel that flows to each primary venturi. 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. Tech Tip #4 Which way to tune the accelerator pump - richer or leaner?. All three systems worked fine except that the off-idle stumble never went away. They also eliminate hesitation and surging, and promote a stable idle and crisp throttle response. I can't call it a victory yet but I'm 98% sure this is the problem. I was running low 1. One of the most innovative manufacturers in the carburetor business is Quick Fuel Technology (QFT). Look into adjusting your throttle plates so they are in the correct position related to the transition slot. mechanical secondary carburetor it may be necessary to change the secondary accelerator pump discharge nozzle restrictions. Had to use secondary throttle blades to set final curb idle. The primary side of the carb is tiny, about 1/3 of the total cfm and uses triple stack boosters giving it incredible atomization velocity and response. What a HUGE improvement off-idle with my new 434 small block. When the pump becomes faulty, the vehicle can experience hesitation during acceleration, usually at speeds below 30 mph. ProMax Performance makes billet throttle plates that have the idle screws relocated closer to the outer edge of the float bowl and can be adjusted easily while running. This often sucks the dirt out of the bleed. Its super easy and quick to change jets and with the turn of s screw you can change when the secondaries open up. If you find that your engine is stumbling off idle and has a hesitation it is because of a carb tuning issue. Step 8: Set your final idle speed. to narrow down what the problem was. The fuel level was set with 6 ½ lbs. works well trans adapt offers 1/2″ laminate type. Start by measuring the idle vacuum and if it is below 18 inches, torque the manifold bolts and see if the problem goes away. This engine was also suffering from a mild off-idle stumble. The return is also located in the tank, hence only one line. 2) If indeed you have enough fuel to stay off the mains, but still have low economy at cruise, you have either too large an idle fuel jet, or too small an idle air jet. We did no adjustments apart from the idle screw. , coil, and 6AL. Holley carbs come with a standard shooter size which differs by carb list#. The dizzy is a fully mechanical Mallory Unilite with a hyfire coil. In conclusion what we've done by advancing the idle timing is burn all the fuel in the combustion chamber, eliminated the rich idle condition and removed the stumble off idle. If the adjustable jet is to the front of the carb,on the side or bottom, it controls the amount of air/fuel mixture going into the engine. we ran a Quick Fuel right out of the box pulled 417. The car would stumble as soon as the throttle was cracked open from idle. At idle I am running 10:1 and cruising is around 10. So I decided to get a new carb and switched from the 600cfm holly to a 600cfm quick fuel. I have a Holley 600 vac sec. But at some point the average owner gets tired of the difficult cold starts, hesitation, less than ideal fuel economy and other carburetor challenges. The idle and off-idle systems are the hardest part of the fuel system to get the fuel curve correct with a blow-through supercharger system, extreme care must be taken to properly size the idle fuel and air restrictions in order to obtain the correct idle and part throttle fuel mixtures. Tuning Carburetors: A Guide for People as Inexperienced as Me. My motor leans out under quick acceleration and I've tried all holly accelerator cams to adjust the pump to get more fuel out of the pump. CB712735 - Quick Fuel Street Series 735 CFM Carburetor - Vacuum Secondary - Electric Choke This Quick Fuel Super Street carburetor offers race performance in a lightweight, street-friendly package. of this fuel is then bled off to an idle well where it is mixed with air from the idle air bleed hole. WOT runs hard no problems. If everything is set up correctly & the carb is sized right, 1-1/2 to 2 turns out is a good starting point. At idle, when the throttle blades are almost closed, the vacuum created by the cylinders causes low pressure in the induction system and activates the idle circuits. idle timing control. Vehicle hesitates immediately off idle. The growth and success of Quick Fuel Technology is attributed to the strength and determination of its staff. 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). No matter how slowly I let out the clutch I still get the stumbling. Quick Fuel’s carburetor technical manager Zach Baker dispelled that myth by saying, “The reality is that there is a huge separation between the efficiency of a street motor and the efficiency of a race motor. I took off the fuel filter, which I'm guess has only been used 200-300 miles city driving. Look into adjusting your throttle plates so they are in the correct position related to the transition slot. Started off with stripping it back to a rolling shell, while all the rust repairs, paint and panel was being completed we built a new 400hp 351 clevo to replace the aging factory 150hp clevo, custom factory looking long range fuel tank, electric fuel pump, exhaust is a full custom mandrel bent stainless system with big extractors and a. Some people think you're supposed to turn the idle mixture screws all the way in, and then back them out 2 1/2 turns. hi nice tech tip ,. Havent had a chance to take it on a longer test drive yet. If you stomp it, it takes off just fine but the car lights the tire when you give it to much gas to get going. This is an easy one. A general rule about setting up carbs is to expect your fuel consumption to rise proportional to newly-found horsepower. Has anyone tried the Quick fuel adjustable metering blocks for a Holley type 4150 carb? I'm running a 650 Speed Demon and I can't get it lean enough at idle no matter what I do. This pair is part# 6282010vb-2 625 cfm 4150 flange,. An emulsified mixture of air and fuel then travels past the. Find Quick Fuel Brawler Street Series Carburetors BR-67212 and get Free Shipping on Orders Over $99 at Summit Racing! Don't let the budget-friendly price fool you--these Quick Fuel Brawler Street Series carburetors are focused on the performance you want and not the pretty box that it comes in. The stock spring in a Holley is plain. Lee Walker from Quick Fuel Technology explains how you can make sure you've got the right jets in your carburetor on race day. If so, you need to open the rear throttle blades a bit. 030) with the L-79 cam (222 @ 50 w/. Help Edelbrock 750, hesitation I have an off idle stumble with my Edelbrock carb and cant seem to cure it. Another good book is the Holley Carb book written by Ulrich and Fisher (spelling may be a little off). Ok I have a brand new quick fuel 650 holley carb. When setting up your carb, the best approach is to set it up on the rich side, then lean it back until you get quick throttle response. The primary throttle blades ( transition slot ) had to be perfectly squared and the mixture screws richer than I liked to eliminated that transition lean stumble. A larger carburetor can create a problem if the converter flash point falls below the peak torque of the engine combination. I checked the codes and nothing came up. A carburetor is specifically designed to do one or the other. QuickFuel 750 rich off idle. It seems like leaving a stoplight over 170° of oil or water temp it wants to stumble & hesitate. clean it out. Part throttle is close to AFR 14 and WOT is still a bit rich at 11. Anyone using a Quick Fuel carb? I also want some particular advice on carb size - the tradeoffs being having enough carb signal, enough to make power at and near redline, but also to have good drivability. Note that I have only purchased a CAN bus cable from Chis, yet he took the time to help me learn. it's like it has asthma. The trimmer still has a hesitation off idle. I have them balanced well and the valves and timing are good. I can richen the idle mixture up and help this problem, but then the idle is way to rich and it will black smoke after idling for about 5-10 seconds. My thought is that if i put the smallest jets avaialbe for the primaries and have the secondaries open up later. Carburetors are pot metal, very weak and easy to. Replace fuel filter and we get a very good stream of fuel when cranking from the hose between pump and carb. How many rpm does the car idle at? If you have the idle screw turned up too much, it will uncover too much of the transfer slot and that will cause a hesitation/bog for sure. It run fairly good. 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). A general rule about setting up carbs is to expect your fuel consumption to rise proportional to newly-found horsepower. I can't get it steadier or higher with idle circuits. Quick Fuel Technology (QFT) has engineered its new Slayer™ series of 600 and 750cfm vacuum secondary street carbs with all the features. What I found was a failing fuel pump. Then it is very simple to tune the carburetor as a single carb engine with no confusion from the other carb. Check float level first by unscrewing sight plugs on fuel bowls. The new idle bypass valve made setting up the idle on the carburetor very easy, and far less complicated than a traditional HP. This assembly delivers an initial shot of fuel in the right amount, and duration, to provide crisp throttle response right off idle. ? Trying to sort out my mates Monaro. you need to go smaller on the leak jet, this will increace the amount of fuel squirt into the intake. most technicians refer to it as a fuel sock. Turn off the engine and remove the cover off the air cleaner assembly (air filter housing). Air to be mixed with idle fuel is provided by the idle air bleed. On Holley Carburetors make sure that you check the accelerator pump adjustment. I got out last night and did a couple of things. Incorrect idle mixture screws - did not fit throttle plate and could not regulate idle fuel flow. The car has a very mild 351C 2V with and Edlebrock Performer, and a 700 Holley double pumper carb. AED Competition Series Award Winning carburetors are all custom built for your specific application. Helpful Information. That would be great if it was that easy. Idle Issues. This test cannot be done accurately when the engine is cold. Also look for. Find Quick Fuel Brawler Street Series Carburetors BR-67212 and get Free Shipping on Orders Over $99 at Summit Racing! Don't let the budget-friendly price fool you--these Quick Fuel Brawler Street Series carburetors are focused on the performance you want and not the pretty box that it comes in. Holley remains the carburetor of choice but there are nice alternatives from Demon, Edelbrock, Summit Racing, Quick Fuel, and Proform. LS1 Carb Intake Kit - Edelbrock Victor Jr/MSD 6014 Ignition/Edelbrock 750 Carb. Not sure what caused the problem, but it's still present, and seems to be causing an extremely rich at idle condition. but same, i feel the engine so rich while running low. Could be a lot of things. You need to blow the debris out of the carb and not into the idle air/fuel well. The WOT air/fuel ratio was only slightly rich at 12. Remove power valve cover. i have moved the throttle accelerator pump lever rod to the closet one to. signal as you come off idle and that would cause a lean condition. Ditch the 800 Edelbrock, and get a Quick Fuel 750 Street Slayer or a Holley 3310-750 cfm. getting fuel smoke from the headers and the plugs are black. 5:1 but under hard acceleration it spikes up to 16:1. This assembly delivers an initial shot of fuel in the right amount, and duration, to provide crisp throttle response right off idle. Some carburetors have a slow speed fuel adjusting screw that regulates the fuel/air mixture in the lower rpm range. 7) Check idle solenoid, especially for power/ground, replace solenoid if necessary. The Power Valve circuit needs to have its flow increased also to bring the primary up to about 35% at WOT. Others have an air adjusting screw. adjusted as best as I can. I've got the standard off idle stumble with a holley carb So basic specs Engine is a 429 Ford, Torker 2 single plane intake, 850 Holley DP with 80 jets front and rear, brown cam in the back, blue in the front, 37 squirters front and back Compression is 10. It appeared to be flooding at idle and the fuel was leaking excessively from the throttle body linkages (on both left & right side). I started driving again. If you throttle engine rapidly from idle it'll stall completely, but if you 'nurse' it up the rev range you can get past the flat spot. 04" front and back. Once the engine is shut off, the fuel in the carburetor bowl begins to evaporate through the bowl vent. Anyway it needs moor fuel in idle. i am not going to say that all of barry grant/ demon products are bad, and i am not going to go into detail. In your case , since this is an intermittent problem - yours has dirt in the circuit. A quick test drive monitored by the Innovate LM-2 delivered some interesting results. "NO , there is only one in each carb, it is not a fuel jet you can change with a screw driver. This engine was also suffering from a mild off-idle stumble. If your car or truck is equipped with a Holley four barrel carburetor and stumbles upon acceleration, more than likely the carburetor needs an adjustment to the accelerator pump assembly. the best type of carb for your app is one with annular boosters. The carb has huge glass sights for the float level, so I could verify that was set properly. In conclusion what we've done by advancing the idle timing is burn all the fuel in the combustion chamber, eliminated the rich idle condition and removed the stumble off idle. So I changed the main jet to170 and moved the needle to the fourth slot from the top. I have the mixture set to the highest idle as well. We also tried a 350 Chevy equipped with a long-duration cam and a Holley 750-cfm 0-3310 vacuum-secondary carb that suffered from a bad off-idle stumble and a pig-rich 10. 0 followed by a test of Quick Fuel’s QFI throttle body fuel injection and most recently I bolted on a different fuel injection system. Slipping clutch so you don't really know what power output is. so i called summit which is where i bought it. i am not going to say that all of barry grant/ demon products are bad, and i am not going to go into detail. This test is being done while the carburetor is on the engine. than expected with weather changes. It is perfectly normal for idle speed to vary as you change the idle mixture screw adjustment. you need to go smaller on the leak jet, this will increace the amount of fuel squirt into the intake. the idle mixture screws are out to 3. No matter what i did it never worked consistently and the off idle stumble seemed uncurable and performance was just lacking. Back off the idle screw to close one carb completely, and set the idle with the second carb only. In your case , since this is an intermittent problem - yours has dirt in the circuit. If there is no fuel in the carburetor, the engine will not start. I am posting this so that someone might avoid the week of headaches I had trying to get rid of an off idle stumble on my '64 Galaxie. Footage taken from Holley Carburetor Installation & Tuning DVD. Hesitation Definition - An engine hesitation is an interruption of continuous power during acceleration. This information was collected from the old suzuki4x4 mailing list at Off-Road. The primary side is the most used and has the idle adjustment that feeds fuel from below the throttle plate. Most of the carburetors need to be re jetted to some extent when dealing with a modified engine. Holley carbs come with a standard shooter size which differs by carb list#. I read the manual backwards and forwards, changed jets and rods, step up springs, idle mixture adjustments, on and on. Start off with. 028 and still very little change. No hesitation or off idle stumble. 025 accelerator pump nozzle-Quick Fuel Technologies secondary diaphragm housing I got it used and rebuilt it when I rebuilt my engine ~5 or 6 years ago. Holley carburetors feature idle mixture screws which control the air/fuel ratio and these are usually the main culprits in an improperly idling carb. This single-stage standard flow power valve boosts your vehicle's power when pulling heavy loads or at fast speeds. this creates a lean off idle mixture. From build invoice 42325. When I leave a stop sign without coming to an absolutely complete stop, it hesitates. The problem I had was with my 1990 NA, which had mysteriously developed a deep hesitation whenever the car moved off from rest. most technicians refer to it as a fuel sock. 5 powervalve, rear has 90 jets no powervalve stock IAB and untouched QF metering block. Typically, racers and engine builders have found this carburetor to be inconsistent which resulted in the fabled "dyno" carburetor that ran very well but was unavailable to the customer. If you stomp it, it takes off just fine but the car lights the tire when you give it to much gas to get going. A sticky or binding TV cable can result in delayed or full throttle upshifts (figure 9). At part throttle while driving you can hear it stumble for a bit. If you find that your engine is stumbling off idle and has a hesitation it is because of a carb tuning issue. The following is just one of a few different ways to check the secondary opening rate/point on an adjustable secondary chamber. A quick test drive monitored by the Innovate LM-2 delivered some interesting results. Now you're ready to reinstall the carburetor and setup your idle system. Atomization Abounds. GAS CARBURETORS MAINTENANCE. When it is idling the engine runs fine without any miss or hesitation. Once the fuel bowls are filled and the engine starts, the float levels are set with the engine running at idle. It sounds like a carb issue from the lean condition your 02 sensor is showing. i am not going to say that all of barry grant/ demon products are bad, and i am not going to go into detail. Quick follow-up. My sparkplugs are normal, throttle input with this 750 cfm on a 468 BBC - performer RPM intake, hydraulic roller, oval port race rite heads in a heavy / automatic trans car is like fuel injection. As the engine is loaded , if it stumbles just off-idle (right when you step on the gas) this means the transition circuit is leaning out too far. Getting 40 mpg and have the idle mixture turned out 3 turns. This information was collected from the old suzuki4x4 mailing list at Off-Road. Verify carburetor is set to stock settings: Idle mixture screw, 11/4 turns from lightly seated. This fast idle and the over rich mixture (due to lack of air), allows the engine to fire up and stay running. Power valve determines when extra fuel is needed. Clamp the ends and connections of the fuel hose. When I leave a stop sign without coming to an absolutely complete stop, it hesitates. Example 3445S. This QFT™ carburetor has been ran on an engine to insure all components are functional. Page 14 of 43 - Les Myers 1989 S10 - posted in Projects: Its sounding like the converter is way to tight. Q: I see the fuel bowls on your race carburetors have dual sight windows. But Moore expected to have to add bypass holes to the new carburetor. Vacuum at idle is between 6. Blow-through carburetors like this Quick Fuel 750 use annular-discharge boosters to deliver a greater volume of fuel to maintain a safe air/fuel ratio at full power. Pull-off or break: The pull-off is manifold vacuum-operated and is designed to open the choke plate slightly after the engine starts, to decrease the signal at the booster. Mid to high rev running is spot on. It would have horrible lean bog and stumble randomly. Once the fuel bowls are filled and the engine starts, the float levels are set with the engine running at idle. Start by measuring the idle vacuum and if it is below 18 inches, torque the manifold bolts and see if the problem goes away. When the engine is cold, more fuel is needed for transition from idle to part-throttle. Air to be mixed with idle fuel is provided by the idle air bleed. Shit canned it for a Quick fuel HR 680. On Holley Carburetors make sure that you check the accelerator pump adjustment. I checked the idle transfer slots, installed the carb, opened up the secondary side a little to raise the idle speed and off I went. Both sides are jetted differently. I see no way an Edelbrock carb will ever be right on one of these cars. Car spits/stumbles at low RPM under acceleration. The SOB would idle right one day and not the next. The idle jet’s up-and-down feed path prevents fuel from siphoning off into the engine from the fuel bowl through the idle circuit. the issue i am having is i have a 1968 charger with a 383 engine stroked to 500 cu in. Top 10 Causes of a Rough Idle | JL Motorworks. all summit holley shoebox carbs have them as well as some quick fuels and some standard holleys. Mine is acting all kinds of stupid right now. Part throttle is close to AFR 14 and WOT is still a bit rich at 11. 5 again and get good idle on 2 counterclockwise screw. But just off idle the engine stumbles. When dyno'd all idle circuits were 1 turn out but now engine is installed I have primary idle screws b/w 1/2 and 3/4 turn out and secondary idle screws at 1/2 turn out. If you attempt to accelerate too hard off idle, to the point where the secondaries kick in, the car bogs and stumbles to the point where it dies unless you lift your foot off the pedal. Elevation is around 400 feet. If not a guess I have to add a gauge but it doesn't sound right since there is no stumble what so ever except for when you barely touch the pedal off idle or in traffic when you get on the pedal again with that light touch. In turn, the AT leans the mixture to attain the proper idle speed. But you might try cranking in about 4 degrees more timing and see what that does. B) At off-idle as the throttle blades begin to open, they uncover the transfer slots which begin to issue fuel, supplementing the discharge from the idle circuits. 035 squirter. Hello all, I have a Quick Fuel SS-750-AN, 750cfm Annular Booster Double Pumper carb on my 340. With a new, clean carburetor such as this Tecumseh 640084B, you can ensure your snowblower starts easily, no matter whether the engine is hot or cold, while also reducing. If you are not sure, take the carb off and turn it over and see where the throttle blade is at on the transfer slot. idle fuel mixture difficult to set with any accuracy. GAS CARBURETORS MAINTENANCE. At part throttle while driving you can hear it stumble for a bit. Then when twisting the throttle it sort of stumbles and spits and crackles before it clears its throat - and then it works fine again! If I have just revved it or have been riding it, and only let it idle for a while it picks up no problem. The only mechanical fuel pump I had go bad would come off idle fine but hard to get any performance out of it so it would starve on the highway. I finally got the stumble out (from cruise to WOT) but then my mileage was terrible (not that we buy these cars for fuel economy, but I was always worrying about running out of gas) I finally got it running lean but stumble is back in a big way. The recommended fuel pressure for this. You have a bad fuel pump. The car would stumble as soon as the throttle was cracked open from idle. The calibration should be very close for all adjustments. If there is no fuel in the carburetor, the engine will not start. Also look for. You can get an off-idle stumble/hesitation/back-fire from both too much squirter as well as not enough. You may have to register before you can post: click the register link above to proceed. Use this information with common sense and at your own risk. I have a quick fuel 650 and it is to rich. _____ Let's use my favorite, a 750 Race Demon with 4-corner idle and full mechanical linkage as an example here. The AVS2 features annular flow primary boosters with a new calibration for improved off idle and cruising performance. Examine the chart below. anyways i. 5 power valve, 71 jets in the front 74 In back. Motivated by this problem, VDL Fuel Systems went to work on producing 4412 carburetors that were repeatable in their performance. be poor and the car might stumble off idle. How to tell what size carb you need: You take the engine cubic inch and multiply by the maximum RPM and divide by 3456. Anyway it needs moor fuel in idle. Those carbs can leak from the bottom and empty the fuel bowl so you have to dump gas in. There is a screw in the bottom of the base plate that pushes open the rear throttle blades. The idle jet's up-and-down feed path prevents fuel from siphoning off into the engine from the fuel bowl through the idle circuit. 5 power valve-green accelerator pump cam-. Use this information with common sense and at your own risk. Retains stock bore and stroke. I can get 20" hg at idle, steady gauge with no fluctuation. Anyway, once you have adjusted the idle mixture screws you should not run rich at IDLE. I've got the standard off idle stumble with a holley carb So basic specs Engine is a 429 Ford, Torker 2 single plane intake, 850 Holley DP with 80 jets front and rear, brown cam in the back, blue in the front, 37 squirters front and back Compression is 10. If not a guess I have to add a gauge but it doesn't sound right since there is no stumble what so ever except for when you barely touch the pedal off idle or in traffic when you get on the pedal again with that light touch. I also noticed at this time the coolant system had a lot of build up and replace and cleaned it all new hoses, thermostat etc. You shouldn't have any vacuum advance at idle. It's a 2 minute call that could save you $100 or more!. Poor gas quality can also be a problem. the idle is to rich. Idle mixture effects idle and to some degree off - idle and very slightly everything else. 030) with the L-79 cam (222 @ 50 w/. The first issues is when you try to "mash the gas hard" it stumbles going from the idle until I pulled the carb off and tinkered with it. A general rule about setting up carbs is to expect your fuel consumption to rise proportional to newly-found horsepower. This leakage can easily be seen while looking down the throat of the carb at idle speeds. The carb has huge glass sights for the float level, so I could verify that was set properly. One sure sign of this is the idle mixture screws do not cause the idle to change when turned in or out. Replace fuel filter and we get a very good stream of fuel when cranking from the hose between pump and carb. If there is no fuel in the carburetor, the engine will not start. Now you're ready to reinstall the carburetor and setup your idle system. Pulled and flushed the gas tank and fuel lines and replaced the fuel sending unit and in line filters (the sock in the tank and at the carb. what could be wrong? I have allready:. Replaced stripped carb air idle mixture screws. 5 powervalve, rear has 90 jets no powervalve stock IAB and untouched QF metering block. If this is your first visit, be sure to check out the FAQ by clicking the link above. Most Holley Street Performance, O. on a mild GMC 302. Incorrect idle mixture screws - did not fit throttle plate and could not regulate idle fuel flow. Low fuel delivery.