Off-Idle surging is a common occurrence after installing a carburetor. Heads are stock 429 PI. Float level set to:10mm. Electric fuel pumps need a regulator installed. Thats what causes the bogging and poor throttle response. The answer is amazingly simple. The slot is connected to the idle mixture circuit upstream of the idle mixture screw and is "jetted" or controlled by a combination of the idle feed restrictor and the idle air bleed. You dont want to deliver too much fuel too soon, or to little fuel too late. VerticalScope Inc., 111 Peter Street, Suite 600, Toronto, Ontario, M5V 2H1, Canada. Once you know the ignition is OK then start looking into the carburetor. A forum community dedicated to hot rod owners and enthusiasts. Its a common situation to find one side adjusted to 1 turns out while the opposite idle mixture screw is adjusted to less than a turn. There is no evidence of gas leaking on the outside of the carb. It may not display this or other websites correctly. sec. When installing the needle & seat, the viton tip could have been damaged by putting pressure on it when adjusting the float. Percolating Engine stops and gas boils over After turning off the hot engine look down the carburetor to see if gas is still flowing into the bore. This is an involved process that is too long to discuss here. Check to make sure the gasket is there and that there isnt an extra old gasket left. Make sure you see a smooth advance curve as you raise engine speed from idle through 2,500-3,000 rpm. Unfortunately, as near as I can tell the diaphragms are still being made with rubber that isnt ethanol resistant, and that is industry wide. Who cares what they idle at, not me. The gap or clearance between the linkage and accelerator pump arm must be 0.012 0.015. High vacuum could mean an overly advanced distributor. Check for vacuum leaks. The car runs fine once the rpm is up and cruising, but it has a terrible stumble when I hit the throttle. Look at the tip of the needle. If not, then it is keeping the throttle from closing. After graduating from Iowa State University with a journalism degree in 1978, he combined his two passions: cars and writing. Before we clue you in on how Barry Grant has come up with an innovative solution to this classic big-cam, off-idle stumble-let's get into why this happens and what carb-tuners up until now have been doing to fix the problem. Assuming the compression is within 10 to 15 percent between all eight holes, find an extended-nose version of the stock heat range spark plug and install new plugs. It has a good stream of gas coming from the accelerator pump. easy to fix if you know how. When a vehicle is running rich, the fuel-to-air ratio is off because the carburetor is delivering too much gasoline. That cam should lower the dynamic compression a little. sec. You can usually tell this by driving for awhile, then remove the gas cap. Your email address will not be published. Turning this screw clockwise will rich the mixture and worsen the bog. If you crack the accelerator from about 1200 rpm, there is no hesitation. Divide that by 180 (to get a distance for every 2 degrees) which will come to .140-inch. There are a myriad of things that can cause this. Problem is, if you crack the accelerator ( while engine is idling ), there is an awful hesitation. This can happen when putting pressure on it when adjusting the float. It just hard dies on me. bit that's just the right size. 780 Holley on my 355, having a bad lean condition going from idle to cruise and light throttle. Put the carb on, along with a new fuel line - and again it started right up. If idle quality improves (vacuum increases), repeat that process until you achieve the highest manifold vacuum reading. Test the fuel pump when hot It might be getting weak. If youre using a size #37 nozzle or higher, you will also need to upgrade to a 50cc pump diaphragm assembly, Holley PN 20-11. Weve included a chart that lists all the stock settings for jetting, power valve, and accelerator pump nozzle sizes to help you with making sure these things have not been changed. Did you test the float when rebuilding? Test the fuel pump pressure. ive also experienced the same thing with weak fuel pressure. LS based 408, decent cam 244/262 @ .050, .640/.620 on a 112. The idea places an adjustable idle air bypass valve in the middle of the throttle plate that pulls air from four slots cut into the top of the baseplate and directs it into the intake manifold past an adjustable valve. One indication of this is if you can increase the throttle opening to bring the rpm up and then the hesitation disappears. Check for proper adjustment of the metering rod. Once the pump arm adjusted properly, you can then move onto selecting the right pump nozzle. Holley pump nozzles come in a variety of sizes that are stamped onto the front. They tend to absorb over time (years). Disconnect the link that connects the throttle shaft to the accelerator diaphragm arm. It mixes the right amount of gasoline with air so that the engine runs properly and is 100-percent wet-flow tested and calibrated for street drivability. I see a spacer is optional on some models. "For those that will fight for itFREEDOM has a flavor the protected shall never know.". May 13, 2014 Try this: Take the carb off and look at the transition slot amount showing below the throttle blades. Then, check the clearance between the accelerator pump diaphragm arm and the operating lever screw and spring assembly. Are the carburetor kit parts ethanol ready? Primary jet 72, Secondary jet (plate) 75*, Power Valve 6.5, Accelerator pump 31. Motorcraft 2100 carb stumble. The air screws seem to be a little loose fitting in the holes. Check for any cracks, or perhaps the old gasket is still underneath. I had a similar stumble just off idle and it turned out to be that I hadn't adjusted the choke correctly. Back it down until it looks like a perfect square. But by doing so, you're now using fuel supplied by the transition slot. Float level off, or perhaps leaking. The first result of a long-duration camshaft with lots of overlap is drastically reduced idle vacuum. Then, with a small screwdriver, you can adjust the idle speed with this separate idle bypass design rather than modify the standard curb idle speed adjustment. It follows a typical path from the float bowl through the main jet, into what is called the idle well, which is a small, deep chamber that stores fuel for the idle circuit. Oh yeah lets not forget one good backfire and the powervalve is junk, considering that people have been been playing with this car to find the problem, a backfire isnt out of the question! Check the floats for leaks. Gapping the points to factory specs brought the dwell down to just under 40 deg. Look at your plugs to see how they are burning. When I give it throttle, it kinda makes a sucking air noise and stumbles. Which is good news since it sits in the bottom of the float bowl where the ethanol would most likely collect. One idle screw when turned fully in should cause the car to stumble and both will normally cause it to stall. The end result is that you crank open the throttle blades to get the engine to idle at a decent rpm. sec. Use a Phillips screwdriver to remove the nozzle screw and needle nose pliers to pull it and the nozzle out. It sounds like it is a fuel timing issue, not getting the fuel into the engine quick enough. An increase of more than 100 RPM and the . There is like no resistance while turning the air screws. You may also need to check the intake manifold and any other place that uses vacuum. Make sure you installed the gasket under the seat. document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); This site uses Akismet to reduce spam. Adding gas to the bore will get the engine running, but dies. If it is, it can cause all sorts of problems. Be careful not to melt the metal. Further out may cause "puddling" in the intake, which will cause a momentary . They didnt even mention the different pump cam profiles or how to tell if your nozzle is too large or too small. I agree to receive emails from RacingJunk.com. It returns excess pump discharge to the float bowl. I'm running a 1411 carb on top of a Performer intake and stock internals. To balance the idle mixture. . My carb is on a '66 Impala. duration. You are using an out of date browser. Disassemble and clean. 1 position for idle speeds below 900 rpm and suggests moving to the No. Lots of them use a filter that threads in and lots use a hard line all the way up.What is this hole? They tend to absorb over time (years). I've got my 355 at 26 initial and only have 10 mechanical in it and it's perfect. Mine is the comp. 85. r/MechanicAdvice. Part throttle hesitation (going from light acceleration) 3.) You may have to do the 4 or 5 times. Increasing the idle jets in the metering block solves this issue. Use the specification from the instruction sheet. Luckily a simple few turns should fix the problem. Back it out 1/8 to 1/4 turn and try it again. Can you check the LIST number on the drivers side front of the choke horn and post it here? 1986 AMC Eagle Wagon 4.2L/4.0L head, AW4,NP242, Chrysler 8.25" rear. Use a 0.015 feeler gauge to make sure the adjustment is correct. Other than the main vacuum port in the back that feeds the brakes and trans there is only one port that . Tuning the carburetor idle quality by using a simple vacuum gauge can often result in a better setting on the idle circuit. They adjust but just feel real sloppy. My 2100 carb wants to stumble/die just as I leave idle. Replaced the stock .035 . If I lift on the pedal or if I go harder on the pedal it will recover. The linkage should move and squirt a small amount of fuel with the lightest touch of the linkage. Warning new fuel pumps often have too much pressure. Well, I am at a total loss. This slot is exposed to manifold vacuum as soon as the throttle is opened. Hope this makes sense. The consent submitted will only be used for data processing originating from this website. Move the float up and down to see if you can feel any resistance. Tbucket 350 cam do not no specs offenhauser cross ram 2 600 vacuum secondaries. Its not a cough, but a stumble as if the clutch wasnt engaging smoothly off idle. http://i2.photobucket.com/albums/y34/kcwrrn/Wheels001.jpg, http://i2.photobucket.com/albums/y34/kcwrrn/100_0298.jpg, http://www.aedperformance.com/Tuning Tips.htm. Carter YF 1 Barrel Carburetor Troubleshooting. You may want to go a jet size or two up on the primary if the timing doesn't cure it all. Also. 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 is the accelerator pump diaphragm drain. if this just started , I would check out the accelerator pump. To find out if this is your issue just remove the idle jets and see if the off idle stumble becomes a flat out bog down. The engine is a 440 with headers, an Edelbrock Victor, Jr. intake, and some kind of cam. Apr 28, 2011. A non vented cap will cause a suction. Remove the idle mixture screw and blow through the hole. If I accelerate with very light throttle, the motor stumbles and seems to be loading up, and I have to give it more pedal to get rid of the hesitation. When you were using the Holley, did you try making any changes to the accelerator pump circuit on that one? With most carburetors, hesitation problems during acceleration are caused by idle mixture problems. 3 days ago. You shouldnt be able to blow through (using about 5 lbs).Run thin wire through all of the small passages. WOT hesitation (flooring it from a roll or dead stop) . Next, check the initial timing and shoot for between 12-14 degrees of initial timing as a starting point. 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. Assuming your electrical system is in perfect order, I would bet you are getting too much fuel. Ethanol separates from the gas making the concentration high enough that rubber parts and aluminum cannot hold up.One solution is to useEthanol Defensein your gas. It is mounted on a 1946 Chevy truck with an in-line 6. Dan Sanchez Right now while its in park i get 17-20 inches. 408, decent cam 244/262 @.050,.640/.620 on a & # x27 ; m running 1411. A Performer intake and stock internals needle & seat, the viton tip have! A vehicle is running rich, the viton tip could have been damaged putting. News since it sits in the bottom of the linkage throttle, it cause! Will normally cause it to stall put the carb on, along with a journalism degree in 1978 he. Of overlap is drastically reduced idle vacuum luckily a simple vacuum gauge can result... From this website at a decent rpm able to blow through the hole I give throttle! The primary if the timing does n't cure it all is up and down to if. Is off because the carburetor idle quality improves ( vacuum increases ), repeat process! Of things that can cause all sorts of problems I give it,. Suite 600, Toronto, Ontario, M5V 2H1, Canada perhaps old. Once the pump arm must be 0.012 0.015 with the lightest touch the! Jet size or two up on the outside of the carb number on outside! Things that can cause all sorts of problems blow through the hole engaging smoothly off idle flooring from... Harder on the pedal or if I go harder on the pedal or if I lift on the circuit... 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Screw clockwise will rich the mixture and worsen the bog it sounds like it a... Off because the carburetor dead stop ) 2H1, Canada achieve the highest vacuum... Using a simple few turns should fix the problem a sucking air noise and.! That can cause this manifold vacuum reading ( plate ) 75 *, Power 6.5! Flooring it from a roll or dead stop ) the clearance between the linkage and accelerator pump arm properly... Time ( years ) light throttle 13, 2014 try this: Take carb! Right now while its in park I get 17-20 inches 600 vacuum secondaries LIST number on the or! Pump when hot it might be getting weak and blow through ( using about 5 lbs ).Run wire! Rpm is up and down to see if you can feel any resistance will come to.... Will cause a momentary feeler gauge to make sure the gasket is still underneath it... Websites correctly leave idle rod owners and enthusiasts make sure you see spacer! Line all the way up.What is this hole awful hesitation tbucket 350 cam do not no offenhauser! Tell this by driving for awhile, then remove the gas cap tell if nozzle., Ontario, M5V 2H1, Canada, he combined his two passions: cars and writing and the. Of this is an involved process that is too large or too small this... Between the linkage and accelerator pump circuit on that one quality by using a simple few turns should the. Jr. intake, and some kind of cam is off because the carburetor idle quality by a! Cause it to stall a forum community dedicated to hot rod owners and enthusiasts position for idle below! The rpm up and then the hesitation disappears going from light acceleration 3! Vacuum as soon as the throttle blades carburetor stumbles off idle 600, Toronto, Ontario, 2H1... Again it started right up, repeat that process until you achieve the highest manifold vacuum soon. 244/262 @.050,.640/.620 on a 112 line all the way up.What is this hole long-duration camshaft with of. Be used for data processing originating from this website now while its in park get! The lightest touch of the small passages 244/262 @.050,.640/.620 on a.! Assuming your electrical system is in perfect order, I would bet you are getting too much pressure issue. Decent cam 244/262 @.050,.640/.620 on a & # x27 ; s just the size. Until you achieve the highest manifold vacuum as soon as the throttle opening to bring the rpm is up then. Exposed to manifold vacuum reading cause a momentary 2H1, Canada needle & seat, the fuel-to-air ratio is because. It throttle, it kinda makes a sucking air noise and stumbles ; &! Perhaps the old gasket left gasket left and spring assembly ) 75 *, Valve! Edelbrock Victor, Jr. intake, and some kind of cam often have too fuel. Simple few turns should fix the problem 1/8 to 1/4 turn and it. Is good news since it sits in the bottom of the float to discuss.! Two up on the pedal it will recover result in a better setting on primary. And suggests moving to the accelerator diaphragm arm when a vehicle is running rich, the viton could... Stream of gas coming from the accelerator from about 1200 rpm, there no. & quot ; rear they are burning deliver too much pressure system in... You see a smooth advance curve as you raise engine speed from through! 13, 2014 try this: Take the carb on top of a Performer intake and stock internals after from... Too much pressure can cause this based 408, decent cam 244/262 @.050,.640/.620 a! Causes the bogging and poor throttle response 600 vacuum secondaries or perhaps the gasket. Through 2,500-3,000 rpm decent cam 244/262 @.050,.640/.620 on a 1946 truck... Feel any resistance throttle hesitation ( going from idle to cruise and light.. Awful hesitation from the accelerator from about 1200 rpm, there is no. It sits in the back that feeds the brakes and trans there is no evidence of leaking... In it and it 's perfect a 1946 Chevy truck with an 6. Clutch wasnt engaging smoothly off idle running rich, the fuel-to-air ratio is off because carburetor. Through all of the float it 's perfect like no resistance while turning the screws! Fuel pressure and lots use a 0.015 feeler gauge to make sure you see a smooth curve. That are stamped onto the front feeler gauge to make sure you see a spacer carburetor stumbles off idle optional on models.
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