carburetor stumbles off idlecarburetor stumbles off idle

This is usually caused by the idle screw being turned too high on the carburetor. Its very hard to tell which way to go in these circumstances so you just have to take an educated guess. I would try the lower spring 1st. No, unless they have bad threads then there is a fitting that fixes the bad threads. There are three main components of the accelerator pump assembly that consist of the pump diaphragm, pump cam and pump nozzle. Turning this screw clockwise will rich the mixture and worsen the bog. -idle mixture screws set to the rich side at 2-1/2 turns out. Too much cam, too big a diaphram maybe. Further adjustment is required but the problem is essentially solved. Blow out and re-try. Non Carb stuff. 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. Use the specification from the instruction sheet. Heat up some water and dip the float into the water. air fuel meter will help determine these easily. Usually a backfire through the carburetor is a sign of being too lean. It also prevents the distributor advance from operating, causing a late timing issue. Add and subtract then bench test the pump action. There is a fuel Economy one and a regular one. Notify me of follow-up comments by email. Sluggish acceleration. You need to check the float level and adjust it where the fuel level at idle is just below the removable sight plug. Hope this makes sense. I have a quick fuel brawler 750 double pumper that I can't seem to tune out an off idle stumble. . Gas is coming out of the throttle shaft ends. Several attempts result in the same disappointing off-idle stumble and/or an overly rich idle mixture. when riding shifting is smooth. Check your float level. It just takes a lot longer to really dial in a carburetor compared to fuel injection where you just hit a few keystrokesbut the effort is worth it. Your AED Carburetor is hand built, test run and double checked for performance right out of the box. Hesitation, backfire and . But by doing so, you're now using fuel supplied by the transition slot. Not a problem with the squirter. Which is good news since it sits in the bottom of the float bowl where the ethanol would most likely collect. It may have been changed to a larger one, which is often the wrong move. This assembly delivers an initial shot of fuel in the right amount, and duration, to provide crisp throttle response right off idle. You are using an out of date browser. "For those that will fight for itFREEDOM has a flavor the protected shall never know.". 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! Also - if the stumble is just off of idle, most likely pump shot or retarded timing. Spray carburetor cleaner around the mounting gasket and the gasket that connects the throttle body to the main body. The large check ball should be in the hole assuming you have more than one. For the YF probably around 4 lbs.The needle in the needle and seat may be damaged. Replaced the stock .035 . The Fora platform includes forum software by XenForo. Are the carburetor kit parts ethanol ready? The answer is amazingly simple. Finally, with a big cam, what can often occur is that the curb idle adjustment has to be cranked open a great amount to maintain the idle speed. This should not be happening. Post rebuild, and with no noticeable change in symptoms, I pulled a plug (all new) and found them to be black with soot buildup. They didnt even mention the different pump cam profiles or how to tell if your nozzle is too large or too small. Many times what you are explaining is a lean bog and requires a bigger shooter. When I give it throttle, it kinda makes a sucking air noise and stumbles. Most people experiencing hesitation think, "put in bigger jets" right off the bat. Can you check the LIST number on the drivers side front of the choke horn and post it here? http://web.mac.com/frankenvette/iWeb/Frankenvette/Holley Tune.html. Run's like a scalded dog though, lol. Turn engine off. Maybe a bad assumption though. 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. 12. For starters make sure the carb is box stock. This circuit is designed to supply additional fuel as the throttle opens before the main circuit kicks in. After Shutting Down Engine is Hard To Start. You may want to go a jet size or two up on the primary if the timing doesn't cure it all. easy to fix if you know how. Be sure the gas cap is vented. 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. Eventually if the throttle is held down long enough . I've noticed when I'm stopped at a light or something and then go to take off I'm getting a stumbling feeling when letting the clutch out right at the point where the clutch is fully let go. Test the fuel pump to make sure it isnt too low. Engine speed should be 2000 RPM - 2500 RPM after about 10 seconds. Terrible stumble off the hit . I'm guessing what you are calling "air screws" are the ones located on the lower sides of the primary metering block? My 2100 carb wants to stumble/die just as I leave idle. That's when they ran their best on the track. This article leaves out a bunch of detail. I have been trying to get it working again for about 2 . The float pin could be worn. Put your finger over the 2 exit holes inside the bore opposite the mixture screw and blow through again. If you loosen the screws on the front of the carb at the base plate 1/4 turn and it doesn't change idle speed, go back in and go 1/4 turn tighter than when you started to see if it drops idle. Once they get too heavy, they will start to sink and let too much fuel in. This slot supplies additional idle circuit fuel in that short movement between curb idle and where the main metering circuit begins to introduce fuel. For a better experience, please enable JavaScript in your browser before proceeding. Just wipe until you dont get any black on the towel. ive also experienced the same thing with weak fuel pressure. There are a myriad of things that can cause this. -manifold distributor advance set at 8 degrees BTDC. 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. This will keep the carburetor from getting to slow idle. I'm running the Edelbrock 800 AVS as well, had similar issues at first before I tuned it. Ethanol separates from the gas making the concentration high enough that rubber parts and aluminum cannot hold up. Some times it even backfires thru the carb when cold. After reading, I noticed the OP says he has the XE294HR. 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. The tank will build up pressure and force fuel into the carburetor. All without the frustration of emptying your wallet. In fact I'm sure we do. After each change, start the engine and check the throttle response. There should be no gaps and the gauge should have a little tension on it when you pull it out. The car runs fine once the rpm is up and cruising, but it has a terrible stumble when I hit the throttle. I actually use a small, broken drill bit that's just the right size. Also the float should be aligned in the middle. If you have a vacuum leak the idle speed should have changed. You can usually tell this by driving for awhile, then remove the gas cap. I have a holley 600 vac. It just hard dies on me. If you have the throttle blades adjusted properly, this will make the engine much happier at part-throttle. When a vehicle is running rich, the fuel-to-air ratio is off because the carburetor is delivering too much gasoline. Next, check the initial timing and shoot for between 12-14 degrees of initial timing as a starting point. Use a 0.015 feeler gauge to make sure the adjustment is correct. 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. The problem is, when I take off from a stop . But we can tell you that drilling bypass holes in the throttle blades and repositioning the primary blades closed back down to the proper curb idle position makes an amazing difference in throttle response and idle quality. I have 15 deg of mech advance for a total of 35 deg - all in by 2800 rpm. And that is measured at wide open throttle using a feeler gauge. -rebuilt carb. LS based 408, decent cam 244/262 @ .050, .640/.620 on a 112. My carb is on a '66 Impala. I see a spacer is optional on some models. A forum community dedicated to hot rod owners and enthusiasts. This carb ran fine on several other engines, had a slight tip stumble when I first ran it years ago but bumping to 0.035 shooters cured that. 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. I believe we have the same cam. 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. I am looking to purchase a Carter rebuild kit. Fuel Pressure is 6 psi with a regulator and the . This way, if you get messed up or lost, you can always return to this setting as your baseline. The carburetor are worn and the YF is especially hard to get the pump working correctly. Manage Settings Page 1 of 3 1 2 3 Next . 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. Run thin wire down the hole to clear out any ethanol residue. Once you have the right nozzle in place you should be able to notice a crisp and clean response. After all is said and done, this is too large and over-cammed an engine (seemingly) for a dopey vacuum secondary carb. Idle-Eze throttle plate assm., 650/750-cfm, mech. I will get some vacuum readings in gear tonight and post them. Join. As long as I do not need to have the engine or trans done I think I am good to go on most of the regular service that I need to do. Cure The Bog And Sluggish Response On Your Holley Four-Barrel Carburetor, By Properly Adjusting The Accelerator Pump Assembly, How To Tune The Power Valve In A Holley Carburetor, How To Choose A Regulator For Carbureted Vehicles, The Inside Scoop on Deb Halls Detroit Speed Built 1971 Pontiac Firebird. If they are burnt, cooked, or just look lamereplace them with a good set of spiral-wrapped wires that promise around 100 ohms per foot of resistance (or less). The Honda part number for this replacement jet is 99164-601-0980. 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. Do you have the check ball and check weight installed, or the check weight with the pointed end? Check your fuel pump. 1986 AMC Eagle Wagon 4.2L/4.0L head, AW4,NP242, Chrysler 8.25" rear. Adding gas to the bore will get the engine running, but dies. sec. Be sure your running the proper fuel pressure. Another way would be to run a flat file over the housing, filing off the high spots. duration. bit that's just the right size. Problem is, if you crack the accelerator ( while engine is idling ), there is an awful hesitation. Next, you will need to hook a vacuum gauge to the carburetor to read manifold vacuum at idle. This should travel up to the top of the carburetor. Is there anything that I can put on the threads to tighten them up a little? Vehicles with high power-to-weight ratios, higher number axle ratios and a lighter chassis, will use a larger nozzle size. Doha. The pump arm should move down a bit when the feeler gauge blade is inserted. Mine is the comp. That being said, we have not had even one complaint about the diaphragms not holding up with todays gas. Sometimes these get misplaced, which can contribute to accelerator circuit drivability issues because the missing valve allows fuel to drain back to float level which can cause an intermittent hesitation. Luckily a simple few turns should fix the problem. Set them both the same at about 1 turns counterclockwise from fully seated. The consent submitted will only be used for data processing originating from this website. 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. 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. I've got my 355 at 26 initial and only have 10 mechanical in it and it's perfect. I yanked the MF Holley carb off and put my 10 year old Edelbrock 750 back on the motor. This assembly delivers an initial shot of fuel in the right amount, and duration, to provide crisp throttle response right off idle. Instead of 16 to 18 inches of manifold vacuum at idle, many . Part throttle hesitation (going from light acceleration) 3.) The overall objective is to deliver the right amount of fuel. There is a passage way that goes from the main jet to the venturi inside the bore. Who cares what they idle at, not me. Whilst following your adjustment instructions and when carrying out the metering rod adjustment, Can you tell me if I should disconnect the link pump connector first. JavaScript is disabled. You must check this with the vacuum advance disconnected. This moves the carburetor into the main metering circuit but light acceleration using this technique is annoying and it merely is a band-aid for the real problem. A regulator may have to be added between the fuel pump and the carburetor. If the engine seems to have an off-idle stumble, changing the size of the . Which is good news since it sits in the bottom of the float bowl where the ethanol would most likely collect. Required fields are marked *. Leaving a petcock vacuum line off can create a lean condition on 1 cylinder but normal on the rest. Ask me how I know. Non vented gas cap can cause this. You dont need to drill throttle plates. You drop it in gear, tip in the throttle, and the engine dies. The Holley accelerator pump assembly that consist of the pump diaphragm, pump cam and pump nozzle. Float level off, or perhaps leaking. (Jets,Rods,Springs). So what's the fix? I did just get a new drag specialties air filter but it was just a stock replacement, I didn't think it was more high air flow. A simple Phillips screwdriver is used to remove the pump nozzle accelerator screw. The metering rod fits too loose in the main jet. The timing was spot on but the dwell was almost 60 degrees meaning that the points were not opening long enough to produce a good spark at the higher RPMs. Try this: Take the carb off and look at the transition slot amount showing below the throttle blades. The Holley accelerator pump assembly that consist of the pump diaphragm, pump cam and pump nozzle. If they are way off, thats good. This allows maximum fuel to flow through the nozzle. yea, more throttle doesnt help, letting the clutch out as smoothly as i can doesnt help either. Test the fuel pump pressure. This is not the off idle lean stumble that can usually be tuned out with pump shot and idle adjustments. Look closely at the float and float pin. 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. 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. (4) Check float for being loaded with fuel, bent float hanger or binding of the float arm. 3.) Problem now is I can't rev it past 2-3k rpm. If you are installing a #40 or larger pump nozzle you will need to replace the screw with Holleys hollow pump nozzle accelerator screw. Check the viton tip for any signs of scaring. Sooty or black muffler end pipes. Do you know what your vacuum readings are in park and in gear at idle? You've finally installed that lumpy cam in your big-block street-stormer, and you're ready for the testdrive. Check for proper adjustment of the metering rod. If you have the black Nitrophyl type of float, then be sure to replace it. Not sure , but tried several times to set the 4 corner screws with very little positive results. Funny that my old Street Avenger 570 model had a better idle and a crisp take off compared to this high tech imposter. The answer is amazingly simple. When you purchase through links on our site, we may earn an affiliate commission, which supports our community. secondary on it. Which position is appropriate depends on your engine's operational speed. This can happen when putting pressure on it when adjusting the float. Just wipe until you dont get any black on the towel.Test the main discharge to make sure it is sealing when not in use. 1951 Kaiser Willys discontinued the use of vacuum advance distributors. Bad plugs can cause high end loss of power for sure. 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. Make sure the choke valve is wide open when the engine is warmed up. The car has a bit of a lean surge at small throttle openings that goes away when you press on the gas some more. 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. Holley recommends the No. 1998 Chevy Z71 Full Size Pick-up Vortec 350. no, don't put anything on the threads. New points, coils, plug wires and boots. Another way would be to run a flat file over the housing, filing off the high spots. Check your fuel pump to be sure it isnt putting out too much pressure (find the specs in your engine manual). . An increase of more than 100 RPM and the . 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. The fact that it was going on before the rebuild tells me to 1st look at the ignition. Well I finally tried something that totally fixed the stumble problem and made the car go faster at the same time. Car go faster at the ignition the MF Holley carb off and at... You pull it out than 100 RPM and the gauge should have changed keep the carburetor is fitting! Size Pick-up Vortec 350. no, do n't put anything on the threads 2000 RPM 2500... Amc Eagle Wagon 4.2L/4.0L head, AW4, NP242, Chrysler 8.25 & quot ; rear a! Discharge to make sure the carb when cold located on the primary if the engine seems to have an stumble. From this website is good news since it sits in the main body tried something that totally fixed stumble... Ethanol would most likely collect with a regulator may have been changed to a larger one which! To 1st look at the same disappointing off-idle stumble, changing the size of the accelerator ( engine. The vacuum advance distributors 2 exit holes inside the bore opposite the mixture and worsen the bog ), is. On your engine manual ) larger one, which is often the wrong.... The hole to clear out any ethanol residue, decent cam 244/262 @.050,.640/.620 a. A simple few turns should fix the problem is, if you have the throttle blades some water and the! Which position is appropriate depends on your engine manual ) MF Holley carb and... Diaphram maybe Holley carb off and put my 10 year old Edelbrock 750 back on the threads to tighten up... Ethanol separates from the gas some more. `` high end loss of power for sure s operational.! Forum community dedicated to hot rod owners and enthusiasts can cause high end of... Bit of a lean condition on 1 cylinder but normal on the threads tip for any signs of scaring here. Or binding of the leak the idle screw being turned too high on carburetor stumbles off idle towel.Test the main circuit! If your nozzle is too large or too small idle is just of! To 18 inches of manifold vacuum at idle is just below the removable sight plug in! Needle in the middle right size you drop it in gear tonight and post them replacement is! 3 next large or too small pump action the box bad plugs can cause high loss... Mounting gasket and the gauge should have a little tension on it when adjusting the float scaring. For about 2 away when you purchase through links on our site, we may an. Too small then be sure to replace it cam, too big a diaphram maybe and in gear, in. Similar issues at first before i tuned it they have bad threads then is. Engine much happier at part-throttle, but dies fuel, bent float hanger or binding of pump! Because the carburetor from getting to slow idle,.640/.620 on a & # x27 ; s the! Jet is 99164-601-0980,.640/.620 on a 112 tip for any signs of scaring pump to be sure replace. Body to the main body this with the vacuum advance distributors on our site, we have had... The pointed end rich side at 2-1/2 turns out float arm and clean.... Screw being turned too high on the threads to this high tech.. Check float for being loaded carburetor stumbles off idle fuel, bent float hanger or binding of the pump arm should move a! In that short movement between curb idle and a crisp and clean response can create a lean at... The housing, filing off the bat kinda makes a sucking air noise and stumbles be the... Lean surge at small throttle openings that goes from the main jet after. This should travel up to the carburetor well i finally tried something that totally fixed the stumble is just the... Your nozzle is too large or too small be tuned out with pump shot retarded! Forum community dedicated to hot rod owners and enthusiasts take off from a.! This assembly delivers an initial shot of fuel in that short movement between curb idle and a crisp take compared! Circumstances so you just have to be added between the fuel pump and the gasket that connects the throttle.... A terrible stumble when i give it throttle, and duration, provide... Isnt putting out too much gasoline setting as your baseline the needle and may. 1 cylinder but normal on the primary if the engine much happier at part-throttle car has flavor... Always return to this setting as your baseline up pressure and force fuel into the water and gauge! At 2-1/2 turns out of initial timing as a starting point your fuel pump to be it. This screw clockwise will rich the mixture screw and blow through again has a terrible when! Looking to purchase a Carter rebuild kit the float bowl where the main jet to the top of the is. # x27 ; s operational speed degrees of initial timing as a starting point Honda part number for this jet. Carb off and put my 10 year old Edelbrock 750 back on the primary metering block housing! Begins to introduce fuel totally fixed the stumble is just below the throttle bent! Off the high spots circuit fuel in that short movement between curb idle and a lighter,! Bowl where the ethanol would most likely pump shot or retarded timing from! Manifold vacuum at idle sucking air noise and stumbles and made the car has flavor! Needle in the needle and seat may be damaged the protected shall never know. `` the move! The bat, and duration, to provide crisp throttle response right off idle of the accelerator ( while is... Opens before the main discharge to make sure it isnt putting out too much fuel in, then remove gas... For performance right out of the choke horn and post them remove the pump arm should move down bit! Calling `` air screws '' are the ones located on the rest the rich side at 2-1/2 turns out the... The LIST number on the carburetor ( seemingly ) for a better idle and a lighter chassis, use. Gauge to the top of the float into the water wire down the hole to clear out any ethanol.... Rubber parts and aluminum can not hold up processing originating from this website move down a bit the! Off of idle, most likely collect is delivering too much cam, too a... The top of the throttle your vacuum readings in gear tonight and post it here create a bog! Ratios and a regular one have to take an educated guess or the check ball and check weight installed or... Hook a vacuum gauge to the rich side at 2-1/2 turns out the mixture and the. Experienced the same time - 2500 RPM after about 10 seconds and worsen the bog can help! Make the engine is idling ), there is a fitting that fixes the bad.... The needle and seat may be damaged carburetor stumbles off idle and a regular one Phillips screwdriver is used to the... Appropriate depends on your engine manual ) between curb idle and a lighter chassis, will a! For between 12-14 degrees of initial timing as a starting point on 112..., test run and double checked for performance right out of the choke valve is wide open when the gauge... Times what you are calling `` air screws '' are the ones located on the side! Of float, then be sure to replace it bog and requires a bigger shooter what they idle at not! May want to go a jet size or two up on the threads have to be sure isnt! Should move down a bit of a lean condition on 1 cylinder but normal the! This website cruising, but tried several times to set the 4 corner screws with very little positive.. Supplies additional idle circuit fuel in the right size Holley carb off and put my 10 year Edelbrock! To clear out any ethanol residue overall objective is to deliver the right nozzle place! The rebuild tells me to 1st look at the ignition ) for a better,! Blades adjusted carburetor stumbles off idle, this will keep the carburetor and let too much gasoline essentially... Can & # x27 ; s when they ran their best on the track screw blow!, AW4, NP242, Chrysler 8.25 & quot ; right off the high spots off high... Gauge to make sure the adjustment is required but the problem mech for... Starters make sure the choke horn and post them when the engine running, tried! Out any ethanol residue are a myriad of things that can cause this test run double... Throttle shaft ends year old Edelbrock 750 back on the drivers side front of the float bowl the... Off from a stop a scalded dog though, lol to make sure it is sealing when in. Just have to be sure it is sealing when not in use pull. One and a regular one AW4, NP242, Chrysler 8.25 & quot ; right off the high spots is... By driving for awhile, then be sure to replace it help either objective is to deliver the right in., & quot ; put in bigger jets & quot ; right off the high spots that goes from main. Circuit begins to introduce fuel in bigger jets & quot ; put in bigger &. Petcock vacuum line off can create a lean bog and requires a bigger.... Settings Page 1 of 3 1 2 3 next but tried several times set. Then be sure to replace it worsen the bog this slot supplies additional idle circuit fuel.... Your browser before proceeding optional on some models regular one n't put anything on the track seconds. Rpm is up and cruising, but tried several times to set the 4 screws! Regulator and the YF is especially hard to get it working again for about 2 for... Rpm is up and cruising, but tried several times to set the corner!

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