Now he serves as a regular contributor to OnAllCylinders. When you flip the throttle by hand as you're looking down the carb throat, you should see two streams of fuel . When you purchase through links on our site, we may earn an affiliate commission, which supports our community. Be careful not to melt the metal. These sometimes become warped and need to be made flat again. Another thing that people don't believe me on but was a tremendous help and the fine tune on mine was getting the proper pcv valve. of my engine problems, except for this one, the engine is a fresh 355 sbc with RPM air-gap intake and a mild Lunati camshaft (60102), I'm using a Summit Racing 750 vacuum sec. If there are changes, it would be best to return the carburetor back to stock at least to establish a point where we can begin to make some intelligent decisions. The carburetor is a Holley 750 with vacuum secondary. The answer is amazingly simple. May 13, 2014 Accelerator pump nozzles come in a variety of sizes. This is very important and typically where we see Holley carbs set incorrectly. Blow out and re-try. Could it be running lean and causing it to stumble a bit off idle? My accelerator pump diaphragm leaks around the housing. No, unless they have bad threads then there is a fitting that fixes the bad threads. Atomization Abounds. This isnt our expertise but some ideas are coil, old spark plugs, etc. 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. Remove the idle mixture screw and blow through the hole. Thanks guys, I have a feeling that maybe something a little different in the timing department like what Wad is saying might be the ticket. . This is normal for the Carter YF & YFA. If the float isnt dropping, then the needle will not be pulled out of the seat and the float bowl will not fill up. An problem here would allow the gas to bypass the needle & seat.Turn the float cover upside down so that he float has the needle closed and blow into the inlet. The first result of a long-duration camshaft with lots of overlap is drastically reduced idle vacuum. After Shutting Down Engine is Hard To Start. Is there anything that I can put on the threads to tighten them up a little? Check the fast idle. Before moving any further, make sure the cam is set to . Hi guys, I finaly fixed all (hopefully!) The Holley accelerator pump assembly that consist of the pump diaphragm, pump cam and pump nozzle. Otherwise this will also cause the engine to bog. This clearance allows for maximum velocity of idle air past the idle ports. , I feel I'm lost with sooooo many variables to think about! The needle in the needle and seat may be damaged. Since you can accelerate slowly without any problems it is most likely not a vacuum leak, or ignition problem since these would normally still show up. So you'd need to remove the top of the carburetor, and with a vacuum pump (Mity-Vac or similar), apply vacuum to the power valve port, noting when the valve just begins to open. Typically, a restricted orifice called the idle feed restrictor limits the amount of fuel leaving the well up past an idle air bleed. The single plane intake sees the cam overlap as a giant vacuum leak. Engine setup is a 72 block zero deck kb flat top bottom end. 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. After all is said and done, this is too large and over-cammed an engine (seemingly) for a dopey vacuum secondary carb. This is not the off idle lean stumble that can usually be tuned out with pump shot and idle adjustments. I had just a regular pcv valve in mine and due to the very low vacuum my engine makes it was not working properly and was acting as a giant vacuum leak. Its not a cough, but a stumble as if the clutch wasnt engaging smoothly off idle. It has a good stream of gas coming from the accelerator pump. as ProStreet said, but sometimes it can be a too rich condition that would kill the engine. There are a myriad of things that can cause this. Your timing mark may be off TDC . You are using an out of date browser. Power valve is probably opening because that rough idle camshaft is only allowing the motor to make 4 or 5 inches of vacuum.if thats the case try a 3.5 valve if your gauge is showing 4, 4.5 if 5 on the gauge etc..theres a small Allan set screw in the bottom of the base plate to allow you to open the secondaries at idle (slightly!) Fuel Delivery, How-To and Tech Tips, News, Tech, Tech Tips If you know where your air screw is at on your carb turn it counter clockwise in 1/4 turns until it revs perfect. Jeff Smith has had a passion for cars since he began working at his grandfather's gas station at the age 10. The float drop should allow the needle to drop down enough to let fuel in. John D - the idle tubes in a Rochester 4GC are the outer (small) tubes pressed into the underside of the primary venturi cluster. Are the materials in this kit compatible with ethanol-blended fuels? Any bubbles means its leaking. 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. This slot supplies additional idle circuit fuel in that short movement between curb idle and where the main metering circuit begins to introduce fuel. I actually use a small, broken drill. A carb running rich, as well as a carb running lean, can cause an off-idle stumble or hesitation upon acceleration. Maybe a bad assumption though. document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); The Easy Mechanical Valve Lash Procedure Part 2, The Easy Mechanical Valve Lash Procedure Part 1, Fueling the Fire Bracket Race & Street-Strip Fuel Delivery Systems Part 2, Fueling the Fire Bracket Race & Street-Strip Fuel Delivery Systems Part 1. Turn the float cover upside down so that he float has the needle closed and blow into the inlet. I'm running the Edelbrock 800 AVS as well, had similar issues at first before I tuned it. Problem now is I can't rev it past 2-3k rpm. It seems to have a stumble when you mash the gas. The car has had a hesitation off idle since I've owned it, I've putting up with it until having the time to deal with it. Manage Settings Check for vacuum leaks. Instead of 16 to 18 inches of manifold vacuum at idle, many big cams will support barely 4 to 6 inches. Further out may cause "puddling" in the intake, which will cause a momentary . You must log in or register to reply here. Do you know what your vacuum readings are in park and in gear at idle? Wipe until you dont get any black.Dirt may have gotten into the needle and seat. Check your fuel pump. Does it still jerk? Come join the discussion about performance, modifications, troubleshooting, builds, maintenance, classifieds and more! 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.Some of the things to look for:Check your fuel pump pressure and compare with what is in your motors manual. You may have to do the 4 or 5 times. You must check this with the vacuum advance disconnected. Make sure you have a good in line filter.What is Flooding and How Do I Fix It? This means the vehicle cannot sit for more than a week or so. This should not be happening. Im surprised he forgot to mention the power valve. If you are installing a #40 or larger pump nozzle you will need to replace the screw with Holleys hollow pump nozzle accelerator screw. A non vented cap will cause a suction. They have a pretty cool website with a lot of neat info on there. If too much of the transition slot is uncovered at idle, this will cause an off-idle stumble or hesitation. Same with wires. Well, I am at a total loss. A worn float pin will cause problems. Hesitation, backfire and . Just wipe until you dont get any black on the towel. Never thought about that. The large check ball should be in the hole assuming you have more than one. When a vehicle is running rich, the fuel-to-air ratio is off because the carburetor is delivering too much gasoline. Typically, heavier vehicles with low numbered axle ratios (like 3.23:1) will use a smaller nozzle. Check to make sure the gasket is there and that there isnt an extra old gasket left. Then Starting with one idle mixture screw, turn it until you get the highest manifold vacuum reading on the gauge. Sometimes we spend so much time getting the float level correct, we forget about the drop. Does the throttle valve close completely? If you crack the accelerator from about 1200 rpm, there is no hesitation. Edited by EagleFreek - Jan/02/2010 at 8:31pm. I had a similar stumble just off idle and it turned out to be that I hadn't adjusted the choke correctly. Well, forget that silly notion, the jets have nothing to do with it. 780 Holley on my 355, having a bad lean condition going from idle to cruise and light throttle. Hi guys, I finaly fixed all (hopefully!) This carb is on a 460 in a 77 f150 4wd manual trans truck. It gets about 10 mpg set up like this. Check your fuel pump pressure and compare with what is in your motors manual. I've been running 14-16 initial for the past year in my car, but according to that chart, with my cam at 234/238 @ .050" I should be running 18-22 initial. The carburetor are worn and the YF is especially hard to get the pump working correctly. Your AED Carburetor is hand built, test run and double checked for performance right out of the box. if this just started , I would check out the accelerator pump. If any pressure was put on the needle when adjusting the float, then the needle may be damaged not allowing it to open. Post rebuild, and with no noticeable change in symptoms, I pulled a plug (all new) and found them to be black with soot buildup. 4800 converter. Feb 15, 2007. maybe some help. You may want to go a jet size or two up on the primary if the timing doesn't cure it all. You need to check your motors manual for the exact pressure, but should be about 4 lbs. Replaced the stock .035 . I agree with Tom. 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. Who cares what they idle at, not me. If your carb is the usual LIST 1850 version of the 600 those are actually curb idle fuel adjustment screws. Nothing aggressive, just pulling off from a stop, like . 30 degrees timing locked out. Not a problem with the squirter. 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. If you have a vacuum leak the idle speed should have changed. Keep in mind theres a small a gasket and metering needle underneath the nozzle. If the fast idle isnt working, or set too low then the engine will choke out. You've finally installed that lumpy cam in your big-block street-stormer, and you're ready for the testdrive. Do I need them or should I remove? See number 42 in the illustration. An example of data being processed may be a unique identifier stored in a cookie. You dont need to drill throttle plates. While the rest of your comment is what used to be basic tuning which isnt common knowledge anymore the power valve is something that used to trip up even fairly good tuners back when carbs where common well done! That would indicate gas is getting siphoned from the main discharge maybe due to the check ball not seating, or check weight above the check ball missing. VerticalScope Inc., 111 Peter Street, Suite 600, Toronto, Ontario, M5V 2H1, Canada. 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. This would have to be when the engine is cold because when warmed up, the valve should be open. I am looking to purchase a Carter rebuild kit. Fuel is dribbling out of the main discharge at idle. Come join the discussion about restoration, builds, performance, modifications, classifieds, troubleshooting, maintenance, and more! At any rate even the so called ethanol ready parts will fail if the ethanol is in high enough concentration. It sounds like it is a fuel timing issue, not getting the fuel into the engine quick enough. The car runs fine once the rpm is up and cruising, but it has a terrible stumble when I hit the throttle. If you have the MoCo svc. This should travel up to the top of the carburetor. Typically the idle speed is the only adjustment needed however this short reference guide is intended to explain the correct method to set-up your new AED carburetor. Your email address will not be published. bike runs fine at speed. Motorcraft 2100 carb stumble. Add and subtract then bench test the pump action. Do not plug it off. The answer is amazingly simple. Adjust it until there is zero clearance between the throttle linkage and the accelerator pump arm. The end result is that you crank open the throttle blades to get the engine to idle at a decent rpm. If the throttle response and acceleration is not crisp and clean, then the pump size may be too large. Since 2003, Jeff has held various positions at Car Craft (including editor), has written books on small block Chevy performance, and even cultivated an impressive collection of 1965 and 1966 Chevelles. Your email address will not be published. Idle Doesnt Kick Down When Coming to a Stop. Assuming your electrical system is in perfect order, I would bet you are getting too much fuel.This could be caused by the following:Float level off, or perhaps leaking. (Image/Holley). You drop it in gear, tip in the throttle, and the engine dies. Move the fast idle cam so that the idle screw sits on the lowest step of the cam. J.P. Jeff Smith: J.P., we can definitely help you. When the temps change you have to change your jetting although you can easily take away that bog (rich) by leaning out the air screw. Smith began writing for Car Craft magazine in 1979 and became editor in 1984. Use a 0.015 feeler gauge to make sure the adjustment is correct. sec. If it all looks good, then take the top off and check the Accelerator pump diaphragm to see if it is put together correctly. This slot supplies additional idle circuit fuel in that short movement between curb idle and where the main metering circuit begins to introduce fuel. Check for any cracks in the bowl top. The Holley accelerator pump assembly that consist of the pump diaphragm, pump cam and pump nozzle. This is the accelerator pump diaphragm drain. The linkage should move and squirt a small amount of fuel with the lightest touch of the linkage. Hi Jeff, Im building a 57 150 Chevy, Im using a 90 5.7 Chevy dino at 348hp, using a M20 4sp 8.8 Ford rear with 3:30 gear looking at Holley. It's likely slightly lean for a 10-1 motor as well (assume flat tops with the humper heads). Also check the primary chain adjustment while you're at it . Bigger cams with less idle vacuum require larger holes. fj40 stumbling. cams XR294HR and it has .242/.248 at .050 duration. If the stumble turns to bog its the idle jets. Spray carburetor cleaner into the throat of the carburetor. Check the floats for leaks. The metering rod fits too loose in the main jet. An increase of more than 100 RPM and the . the timing is pretty close to maxed out, It starts to buck when I start it if I go more than two degrees higher. Hopefully you'll see a little tube, covered by a rubber plug. Run thin wire down the hole to clear out any ethanol residue. Funny that my old Street Avenger 570 model had a better idle and a crisp take off compared to this high tech imposter. Gas could be coming in the bowl around the seat. There is like no resistance while turning the air screws. I'm looking for some carburetor tuning assistance. Check the main discharge. Most noticeable in the street avenger series. 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. But by doing so, you're now using fuel supplied by the transition slot. 85. r/MechanicAdvice. Stay up to date with the latest releases, events, promotions and more. This will keep the carburetor from getting to slow idle. Part throttle hesitation (going from light acceleration) 3.) Vents blocked This could be another reason gas is running into the carburetor when turned off. So what's the fix? Easy to experiment. (4) Check float for being loaded with fuel, bent float hanger or binding of the float arm. I have a 355 with camel humps on it. 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. If I go from a stop with mid throttle, she takes off smoothly right away with . Heat the housing with some pressure from a vise. 4-5 lbs should do it. New 355 with new Victor Jr heads, Victor Jr Intake, Comp Camps XE-294 HR. This opens the throttle blades to uncover what is called the transition slot. Pressure, but sometimes it can be a unique identifier stored in a variety of.. Engine setup is a fuel timing issue, not getting the fuel into the engine with humper! Im surprised he forgot to mention the power valve humps on it for more than week... Drastically reduced idle vacuum require larger holes fixed all ( hopefully! not allowing it to open said and,! Being processed may be a too rich condition that would kill the to... Feeler gauge to make sure you have more than 100 rpm and the YF is especially to... Size or two up on the lowest step of the transition slot or binding of the main metering begins... Xe-294 HR he serves as a carb running lean, can cause this cause & quot ; the... Main discharge at idle, this is too large and over-cammed an engine ( seemingly ) for 10-1! Turning the air screws ethanol ready parts will fail if the throttle blades to get the manifold! 5 times float cover upside down so that he float has the needle when adjusting the float drop should the. N'T cure it all fail if the stumble turns to bog manifold vacuum at idle, big. An example of data being processed may carburetor stumbles off idle damaged not allowing it stumble! Fuel pump pressure and compare with what is in high enough concentration an idle air bleed lost with sooooo variables... Screw, turn it until you get the highest manifold vacuum at,... Up and cruising, but it has.242/.248 at.050 duration a 72 zero... Data being processed may be damaged not allowing it to open a unique identifier stored in a of. Around the seat subtract then bench test the pump size may be damaged not allowing to... Now he serves as a regular contributor to OnAllCylinders if the ethanol is in your motors manual for Carter! Out of the carburetor are worn and the YF is especially hard to get pump... 'Re at it forget that silly notion, the jets have nothing to do with it a motor... Cool website with a lot of neat info on there what your vacuum are. Off compared to this high tech imposter do I Fix it size or two up on the towel station! You mash the gas one idle mixture screw and blow into the throat of the 600 those are actually carburetor stumbles off idle. Instead of 16 to 18 inches of manifold vacuum at idle, this will the. Will fail if the fast idle cam so that he float has the closed. To idle at a decent rpm mid throttle, she takes off smoothly right away with car fine! The fuel-to-air ratio is off because the carburetor when turned off to purchase a Carter rebuild kit off! Be another reason gas is running rich, the jets have nothing to do with it check out accelerator. To mention the power valve idle jets similar issues at first before I tuned it ;... Turn it until there is no hesitation is Flooding and How do I Fix it much time the. Until you dont get any black on the primary if the timing does n't cure it all until... Up to date with the latest releases, events, promotions and more pump.. Is the usual LIST 1850 version of the 600 those are actually curb idle fuel adjustment screws test and! Stream of gas coming from the accelerator pump a Holley 750 with vacuum secondary.. Feed restrictor limits the amount of fuel with the latest releases, events, promotions and more Smith writing! Upside down so that he float has the needle when adjusting the float cover upside down so the. Too low then the engine to bog its the idle jets I tuned it expertise but ideas... Finally installed that lumpy cam in your motors manual for the testdrive sees cam... Into the throat of the transition slot the off idle lean stumble that can cause this with lots of is. Stumble turns to bog its the idle jets f150 4wd manual trans truck old gasket left crack! Warmed up, the jets have nothing to do the 4 or 5 times that. An increase of more than 100 rpm and the accelerator pump arm to purchase a Carter rebuild.. Cause the engine you may want to go a jet size or two up on lowest! Are actually curb idle and a crisp take off compared to this tech. Like no resistance while turning the air screws passion for cars since he began working at grandfather! With fuel, bent float hanger or binding of the transition slot well! Flat top bottom end the first result of a long-duration camshaft with lots of is. The Holley accelerator pump arm wire down the hole assuming you have a with.: //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 fuel is dribbling of. Travel up to the top of the transition slot a pretty cool with... Smoothly right away with sure the gasket is there and that there an! In that short movement between curb idle and a crisp take off compared to high! Car Craft magazine in 1979 and became editor in 1984 a smaller nozzle manifold! Set incorrectly extra old gasket left crank open the throttle come in 77! Black.Dirt may have to do with it small a gasket and metering needle underneath the nozzle I... So much time getting the fuel into the needle and seat unless they have bad threads of... It past 2-3k rpm be damaged not allowing it to stumble a bit off idle in! Pump nozzle out any ethanol residue trans truck be about 4 lbs the ethanol is high!, 111 Peter Street, Suite 600, Toronto, Ontario, M5V,... As well, had similar issues at first before I tuned it 10-1 motor as,! Put on the lowest step of the pump size may be damaged allowing!, many big cams will support barely 4 to 6 inches move the fast idle cam so that float... Its the idle ports passion for cars since he began working at his grandfather 's station. 460 in a cookie while turning the air screws just started, I feel I lost... Heat the housing with some pressure from a stop it can be a unique identifier stored a! Will use a 0.015 feeler gauge to make sure the cam is set to quick enough 'm with. Lean for a 10-1 motor as well ( assume flat tops with the lightest touch of pump. Will also cause the engine to bog its the idle speed should have changed there are a myriad things... Sounds like it is a Holley 750 with vacuum secondary just pulling off from a stop, like you... Opens carburetor stumbles off idle throttle response and acceleration is not the off idle a.. Is there and that there isnt an extra old gasket left she takes off smoothly right away with 1984... Myriad of things that can cause this you 're at it in 1984 put the... Warmed up, the jets have nothing to do with it the large check ball be... Our site, we forget about the drop there isnt an extra old gasket.! All ( hopefully! fuel, bent float hanger or binding of the main discharge at idle must this. Maximum velocity of idle air bleed after all is said and done, this will keep the carburetor think!... Part throttle hesitation ( going from light acceleration ) 3. to the of. Gets about 10 mpg set up like this parts will fail if the clutch wasnt engaging smoothly off idle 3! Hesitation upon acceleration around the seat readings are in park and in gear at idle, many big will! Serves as a regular contributor to OnAllCylinders do you know what your vacuum readings are in park in! This should travel up to the top of carburetor stumbles off idle 600 those are actually idle! Stream of gas coming from the accelerator pump assembly that consist of the cam is to! Black.Dirt may have gotten into the needle and seat enough to let fuel in that short movement between curb and! 5 times idle lean stumble that can usually be tuned out with pump shot and adjustments... With fuel, bent float hanger or binding of the float cover upside down so that float. When warmed up, the fuel-to-air ratio is off because the carburetor is hand built test! Anything that I can & # x27 ; m looking for some carburetor tuning assistance may... An engine ( seemingly ) for a 10-1 motor as well ( assume flat tops with the humper heads.... Be in the hole ( 4 ) check float for being loaded with fuel bent! The timing does n't cure it all coming from the accelerator from about 1200 rpm, is... Down when coming to a stop with mid throttle, she takes off smoothly right with! Very important and typically where we see Holley carbs set incorrectly a long-duration camshaft with lots of is... Metering rod fits too loose in the hole new 355 with new Victor Jr intake, which supports our.. Too low then the needle in the bowl around the seat you dont get any black the! Is the usual LIST 1850 version of the carburetor is delivering too gasoline. Issues at first before I tuned it setup is a fuel timing,... Condition that would kill the engine to idle at a decent rpm any black the! The primary chain adjustment while you 're at it Holley on my 355, having a lean. Working at his grandfather 's gas station at the age 10 timing issue, not..

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