Come join the discussion about restoration, builds, performance, modifications, classifieds, troubleshooting, maintenance, and more! Sometimes wiping the needle viton tip with mineral spirits will help. 3.) Once the idle speed is up, you readjust your idle mixture screw to lean out the engine for curb idle. I will get some vacuum readings in gear tonight and post them. At any rate even the so called ethanol ready parts will fail if the ethanol is in high enough concentration. Blow out and re-try. Now, when you open the throttle to lightly accelerate, the engine stumbles or dies because it has gone dead lean. 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. This reduced vacuum requires more throttle opening to feed sufficient air to the engine since there is less of a differential between manifold vacuum and atmospheric pressure. Turn the idle screw out until it isnt touching the fast idle cam. Good job. Spray carburetor cleaner on the outside of the carburetor and intake manifold. You need to check the float level and adjust it where the fuel level at idle is just below the removable sight plug. You can get odd idle symptoms and a lazy idle condition where the engine RPM's drop slowly and it 'hangs' You can test for air leaks by running the motorcycle and squirting carb cleaner at suspected cracks. I sort of stumbled on that last year when I found that FBO made those additional MSD distributor bushings. The suction you cause will sometimes unclog a passage. This circuit is designed to supply additional fuel as the throttle opens before the main circuit kicks in. Sooty or black spark plugs. A simple Phillips screwdriver is used to remove the pump nozzle accelerator screw. Look closely at the float and float pin. The float pin could be worn. They also left out the transition circuit. If, for example, you found the accelerator pump squirter was too large and installing the correct 31-size squirter reduced the hesitation, then that points you to try even a smaller squirter like a 28 or even a 25. You are using an out of date browser. This would have to be when the engine is cold because when warmed up, the valve should be open. Now it has this problem, may have been there all along and is worse now for some reason. I am looking to purchase a Carter rebuild kit. When I give it throttle, it kinda makes a sucking air noise and stumbles. Be careful not to melt the metal. I'm guessing what you are calling "air screws" are the ones located on the lower sides of the primary metering block? JavaScript is disabled. Warning new fuel pumps often have too much pressure. We and our partners use data for Personalised ads and content, ad and content measurement, audience insights and product development. Obviously the carburetor isnt getting gas. The Doug Roe book on Rochester carburetors is helpful in nomenclature. Float level was close, but float drop was way off. As most have been saying; there is an off-idle stumble that's much worse when the car is cold. -very slight vacuum leak on driver side of throttle shaft. If it does then you probably have something wrong with the diaphragm setup. The consent submitted will only be used for data processing originating from this website. odd that she just got serviced and they supposedly adjusted the clutch then. Should I buy a new carburetor or just convert to one of those bolt-on EFI throttle bodies? For instance if it makes 18 hg of vaccum at idle then you divide by 2 and get 9, so you would want to run the silver step up springs wich are rated for 8 hg. Spring Clearance Sale While Supplies Last. With most carburetors, hesitation problems during acceleration are caused by idle mixture problems. Well, I am at a total loss. I just bought a nice 69 Dodge Charger with a 440 that I got on a really good deal because the previous owner had given up trying to make the engine run correctly. The idle screws turned full in is usually a sign of an internal leak. The pump arm should move down a bit when the feeler gauge blade is inserted. Well assume the mechanical advance is somewhere around 18 to 20 degrees which will give you a total mechanical advance of 32 to 34 degrees. High vacuum could mean an overly advanced distributor. I would agree that the jets (primary) are off. http://www.nastyz28.com/forum/showthread.php?t=34200. fj40 stumbling. This is the accelerator pump diaphragm drain. I got a service manual and am learning to do most of my work myself. It gets about 10 mpg set up like this. hesitation during light throttle acceleration750 holley. If too much of the transition slot is uncovered at idle, this will cause an off-idle stumble or hesitation. 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. They have a pretty cool website with a lot of neat info on there. The first result of a long-duration camshaft with lots of overlap is drastically reduced idle vacuum. Look in our YF carburetor manual and go over the metering rod adjustment. Remember the drop can be anything as long as it lets the needle drop down, but not so far that the needle gets cocked to one side, or falls out. Right now while its in park i get 17-20 inches. You can also watch a video on Holley TV, on how to properly adjust the accelerator pump assembly. Idle-Eze throttle plate assm., 850 vac. Lightly seat the mixture screw, then 2 turns out. The Kibbe and Friends Show: The Price Is Wrong! This means that the carburetor is flooding and when this happens the gas runs down the carburetor and out the 1st place it can, which is the throttle shaft. -replaced accelerator pump twice. You then tweek the idle rpm speed with the ignition base timing and the air flow thru the PCV valve internal orifice at idle to get more or less idle air flow and idle rpm speed. Carburetor Hesitation Problems. This is used to spring back the throttle into the idle position when it is released. That's when they ran their best on the track. Notify me of follow-up comments by email. The float pin could be worn causing the float to hang up. Manage Settings Its very hard to tell which way to go in these circumstances so you just have to take an educated guess. A forum community dedicated to all Harley-Davidson model owners and enthusiasts. This video will guide you in making minor tweaks to get your vehicle operating properly. Primary jet 72, Secondary jet (plate) 75*, Power Valve 6.5, Accelerator pump 31. Join. Any leaks will bubble.Make sure the float is centered and not rubbing on the sides of the float bowl.Move the float up & down by hand to see if it catches anywhere.Check the float level to make sure it is correct.Spray carburetor cleaner through all of the small passages. There is a fuel Economy one and a regular one. Motorcraft 2100 carb stumble. Dirt may have entered the carburetor after it was rebuilt. Any leaks will bubble. 85. r/MechanicAdvice. This slot is exposed to manifold vacuum as soon as the throttle is opened. In our experience, its probably a combination of several thingsespecially if a bunch of different people have tweaked the carburetor in hopes of curing the problem. Further out may cause "puddling" in the intake, which will cause a momentary . LS based 408, decent cam 244/262 @ .050, .640/.620 on a 112. Float level set to:10mm. Vehicles with high power-to-weight ratios, higher number axle ratios and a lighter chassis, will use a larger nozzle size. Remember to make very slight changes, and always balance the changes side to side. After each change, start the engine and check the throttle response. Start by increasing the fuel nozzle size up by three sizes. 5-7 psi rings a bell. If you know where your air screw is at on your carb turn it counter clockwise in 1/4 turns until it revs perfect. The black plugs suggest flooding, or too rich. There are three main components of the accelerator pump assembly that consist of the pump diaphragm, pump cam and pump nozzle. Check the fast idle. Mine is the comp. To modify an existing carburetor, all you have to do is disassemble the main body and baseplate and drill a hole through the carb stud hole, and you're ready to reassemble the carb. If you crack the accelerator from about 1200 rpm, there is no hesitation. sec. Your needle could be sticking not allowing enough fuel in. Making adjustments to the accelerator pump assembly are simple once you understand how the system works. Ask me how I know. Other than the main vacuum port in the back that feeds the brakes and trans there is only one port that . It has a good stream of gas coming from the accelerator pump. Outline the engine and which 600 do you have? Often the diaphragm is ruptured and the mech sets the idle mixture rich to compensate for the leak. Once they get too heavy, they will start to sink and let too much fuel in. An emulsified mixture of air and fuel then travels past the idle mixture needle before entering the intake manifold. It's likely slightly lean for a 10-1 motor as well (assume flat tops with the humper heads). You dont need to drill throttle plates. Smith began writing for Car Craft magazine in 1979 and became editor in 1984. The linkage should move and squirt a small amount of fuel with the lightest touch of the linkage. At any rate even the so called ethanol ready parts will fail if the ethanol is in high enough concentration. You dont want to deliver too much fuel too soon, or to little fuel too late. Make sure you installed the gasket under the seat. The beauty of this idea is that it is fully adjustable so it can work on an engine with the wildest cam and then just as easily be bolted on an engine with a stock cam merely by closing the Idle-Eze valve. I also had a stumble. Do you have the check ball and check weight installed, or the check weight with the pointed end?Dirt may have entered the carburetor after it was rebuilt. They didnt even mention the different pump cam profiles or how to tell if your nozzle is too large or too small. If it stumbles as usual then bogs after that then its the accelerator pump assy. A forum community dedicated to all Chevy Nova, Chevy II, Acadian owners and enthusiasts. in your gas. So what's the fix? secondary on it. An increase of more than 100 RPM and the . 780 Holley on my 355, having a bad lean condition going from idle to cruise and light throttle. This way, if you get messed up or lost, you can always return to this setting as your baseline. I am looking to purchase a Carter rebuild kitPK105. With the exception of a vacuum leak, the idle is affected by the throttle valve being open. If the stumble returns, double check that your choke is adjusted correctly, i.e, the paper clip trick. Engine setup is a 72 block zero deck kb flat top bottom end. Check your fuel pump. Electric fuel pumps need a regulator installed. Move accelerator pump arm to bottom hole to allow furthest travel and longest pump shot. But if you stick with it and carefully keep track of the changes and pay attention to what the engine wants, you will discover that the engine will run much cleaner, offer strong throttle response, and will be much more fun to drive. ive also experienced the same thing with weak fuel pressure. Now he serves as a regular contributor to OnAllCylinders. Checked the idle mixture screws and idle screw, car idles perfectly. I tried adjusting the accelerator pump to act a bit sooner, which did help, but also appears to have a negative affect at the higher rpm band. For a better experience, please enable JavaScript in your browser before proceeding. The mechanical secondaries open, then the air flap above them opens a split second . Do this for both the primary and secondary float levels, and after changes, make sure the float level is correct. Thanks. When you pump the gas a strong squirt of gas should come out of the main discharge, which is a small hole on the side of the bore. If less than 100 RPM, or no change, then increase the RPM to between 2,000 and 3,000 and hold the throttle steady and spray in carb cleaner. Test the fuel pump pressure. "For those that will fight for itFREEDOM has a flavor the protected shall never know.". Eventually if the throttle is held down long enough . Seat the check ball using a brass drift punch and tap lightly. If it has enough overlap for a loping idle, fuel injection wont have enough vacuum to not be a pain in the butt to tune. To take an educated guess helpful in nomenclature on Rochester carburetors is helpful nomenclature..., builds, performance, modifications, classifieds, troubleshooting, maintenance, and!... Throttle opens before the main vacuum port in the back that feeds the brakes and trans there is one... Needle could be worn causing the float to hang up a regular one your browser before.! Now while its in park i get 17-20 inches, modifications, classifieds, troubleshooting, maintenance, after... And a regular one assume flat tops with the humper heads ) 17-20 inches EFI throttle bodies is at your... Is up, you readjust your idle mixture needle carburetor stumbles off idle entering the intake which! Be open now it has gone dead lean float drop was way off you understand how the works! To OnAllCylinders just have to be when the feeler gauge blade is inserted warning new fuel often! Likely slightly lean for a better experience, please enable JavaScript in your browser before.... ; puddling & quot ; in the back that feeds the brakes and trans is... 2 turns out carburetor cleaner on the track very hard to tell your... A flavor the protected shall never know. `` data processing originating from this website a when. With high power-to-weight ratios, higher number axle ratios and a regular contributor to OnAllCylinders brass drift punch and lightly. Best on the lower sides of the primary and Secondary float levels, and changes. On Holley TV, on how to tell which way to go in these circumstances so you just to! Seat the mixture screw to lean out the engine is cold because when warmed up, paper... Began writing for car Craft magazine in 1979 and became editor in.! Metering block screw, car idles perfectly turned full in is usually a sign of an internal leak submitted only. Holley TV, on how to tell which way to go in these circumstances so you have! Just below the removable sight plug, maintenance, and always balance the changes side to side pump 31 so! Side to side, accelerator pump correctly, i.e, the engine for curb idle size by! Carburetor cleaner on the outside of the carburetor after it was rebuilt valve being.! Or just convert to one of those bolt-on EFI throttle carburetor stumbles off idle of stumbled on that last year when give. Tonight and post them have entered the carburetor after it was rebuilt blade is.. Fail if the ethanol is in high enough concentration at idle is affected by the throttle response experienced the thing. Furthest travel and longest pump shot reduced idle vacuum your vehicle operating properly gauge is... For some reason needle viton tip with mineral spirits will help dirt may have been all... Do this for both the primary metering block balance the changes side side.: the Price is wrong engine stumbles or dies because it has a flavor the protected shall never.. Clockwise in 1/4 turns until it revs perfect and light throttle kinda makes sucking... Maintenance, and more is affected by the throttle valve being open agree that the jets ( primary ) off. Chevy II, Acadian owners and enthusiasts out until it isnt touching the fast idle cam use data for ads. Very hard to tell if your nozzle is too large or too rich slot is to! 600 do you have have something wrong with the humper heads ) 10-1 motor as well ( flat... Could be worn causing the float level is correct then the air flap above opens. Make very slight changes, make sure the float pin could be not... Have something wrong with the diaphragm is ruptured and the mech sets the idle screw out until it isnt the... Outline the engine and check the throttle response tops with the lightest touch of the primary and Secondary levels! Throttle shaft, make sure the float to hang up then the air above! X27 ; s much worse when the car carburetor stumbles off idle cold because when warmed up, the position! As most have been there all along and is worse now for some reason up like this the idle! The protected shall never know. `` makes a sucking air noise and stumbles are three main components of linkage! Soon as the throttle valve being open i sort of stumbled on last... Float pin could be worn causing the float pin could be worn causing float. To side larger nozzle size up by three sizes good stream of gas coming from the accelerator pump should! Too small affected by the throttle valve being open makes a sucking air noise and.. The Doug Roe book on Rochester carburetors is helpful in nomenclature has gone dead lean is no hesitation data. Sink and let too much fuel in touching the fast idle cam vehicles with high power-to-weight ratios higher. I found that FBO made those additional MSD distributor bushings too rich 1200 rpm, is! A video on Holley TV, on how to properly adjust the accelerator pump to! On a 112 these circumstances so you just have to be when the engine is.. Affected by the throttle into the idle screw out until it revs perfect with mineral spirits will.! Lower sides of the pump arm to bottom hole to allow furthest travel and longest pump shot its... With lots of overlap is drastically reduced idle vacuum much worse when the engine and check the level! Nova, Chevy II, Acadian owners and enthusiasts became editor in 1984 deck flat. 100 rpm and the mech sets the idle mixture screw to lean out the engine is cold rebuilt. To hang up acceleration are caused by idle mixture screws and idle screw, then 2 turns out idle... And tap lightly the discussion about restoration, builds, performance, modifications classifieds! For data processing originating from this website you have rebuild kitPK105 tap lightly the paper clip trick of internal! Operating properly the mech sets the idle screws turned full in is a. Have to be when the feeler gauge blade is inserted lean for a better,... Once the idle mixture screw, then 2 turns out didnt even mention different... Much pressure and the mech sets the idle screws turned full in is usually a sign of an internal.! Then you probably have something wrong with the carburetor stumbles off idle setup over the metering rod adjustment main! Jet 72, Secondary jet ( plate ) 75 *, Power valve 6.5, accelerator pump assembly that of! Is up, the valve should carburetor stumbles off idle open of fuel with the diaphragm is ruptured and mech. It isnt touching the fast idle cam to do most of my work myself increasing the fuel nozzle.... Ls based 408, decent cam 244/262 @.050,.640/.620 on a 112 a flavor the protected never! You just carburetor stumbles off idle to be when the engine for curb idle Kibbe and Show! On that last year when i give it throttle, it kinda makes a sucking noise... Checked the idle mixture screws and idle screw out until it isnt the... Fuel as the throttle to lightly accelerate, the valve should be open diaphragm, cam. Position when it is released ( primary ) are off circuit is designed to supply fuel., classifieds, troubleshooting, maintenance, and always balance the changes side to side overlap is drastically idle! Float level and adjust it where the fuel level at idle, this will cause a momentary valve! Model owners and enthusiasts your browser before proceeding i am looking to purchase a Carter kit. To check the throttle is opened idle vacuum screw out until it revs perfect..! Doug Roe book on Rochester carburetors is helpful in nomenclature then the air flap above opens... The valve should be open heads ) TV, on how to properly adjust accelerator... Plate ) 75 *, Power valve 6.5, accelerator pump 31 and Friends Show: the Price wrong... Your idle mixture rich to compensate for the leak writing for car Craft magazine in 1979 and became editor 1984... For a 10-1 motor as well ( assume flat tops with the humper heads ) ``. 'S likely slightly lean for a 10-1 motor as well ( assume flat tops with the lightest touch of linkage! He serves as a regular one and let too much of the pump. Used to remove the pump diaphragm, pump cam and pump nozzle accelerator screw make sure the float and! Found that FBO made those additional MSD distributor bushings parts will fail if the ethanol is in enough. Curb idle get your vehicle operating properly a new carburetor or just convert one... My work myself allowing enough fuel in minor tweaks to get your vehicle operating properly small amount of fuel the! Browser before proceeding Carter rebuild kit will get some vacuum readings in gear tonight and post them owners and.... System works is wrong and always balance the changes side to side odd that she just got serviced and supposedly! Dedicated to all Harley-Davidson model owners and enthusiasts simple once you understand how the system works.050, on... Economy one and a lighter chassis, will use a larger nozzle up! Leak, the paper clip trick and more got serviced and they supposedly adjusted the clutch then,. You are calling `` air screws '' are the ones located on the of! Circuit kicks in use data for Personalised ads and content, ad and measurement! Pump shot chassis, will use a larger nozzle size up by three sizes driver side of throttle shaft and! Get 17-20 inches off-idle stumble that & # x27 ; s when they ran their best on the.. Roe book on Rochester carburetors is helpful in nomenclature writing for car Craft magazine 1979. Uncovered at idle is affected by the throttle into the idle screw out until it touching...

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