Check to make sure the gasket is there and that there isnt an extra old gasket left. sec. odd that she just got serviced and they supposedly adjusted the clutch then. My suggestion is make sure you have a proper pcv valve, then advance initial timing, try larger squirter in that order. Big Cam BluesSo why doesn't this circuit work on an engine with a big cam? Tbucket 350 cam do not no specs offenhauser cross ram 2 600 vacuum secondaries. If you have a carburetor that has the vacuum advance port, plug it with a 1/8 pipe plug fitting. I have been trying to get it working again for about 2 . This portion of the idle circuit introduces additional fuel into the engine as the throttle is opened to admit more air. Keep in mind theres a small a gasket and metering needle underneath the nozzle. That's usually a lean condition. It is mounted on a 1946 Chevy truck with an in-line 6. 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. My 2100 carb wants to stumble/die just as I leave idle. Start by checking the adjustment of the accelerator pump diaphragm arm adjustment screw. This is normal for the Carter YF & YFA. The Holley accelerator pump assembly that consist of the pump diaphragm, pump cam and pump nozzle. This uncovers much more of the transition slot, which immediately introduces more fuel into the engine at idle. For now, Grant has adapted the Idle-Eze idea on new throttle plates available for most of the larger Demon carburetors. Heat up some water and dip the float into the water. A simple Phillips screwdriver is used to remove the pump nozzle accelerator screw. This will be our starting point. You can try wiping off the viton tip with mineral spirits. Assuming the electrical system is working correctly then you either have a vacuum leak, or not getting enough fuel. Instead of 16 to 18 inches of manifold vacuum at idle, many . Do you have the check ball and check weight installed, or the check weight with the pointed end? Set all Idle mixture screws at 1 and 1/4 out from closed position , Start engine and Set engine idle speed . Spray carburetor cleaner into the throat of the carburetor. Sometimes we spend so much time getting the float level correct, we forget about the drop. Keep in mind that the idle screw opens the throttle valve, which speeds up the RPM. Come join the discussion about performance, modifications, classifieds, troubleshooting, maintenance, and more! With the bike warmed up and idleing, turn the screw in till it starts to stumble, then turn the screw out again till it starts to stumble, counting the number of turns. 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. This slot is exposed to manifold vacuum as soon as the throttle is opened. There are certain vents that if plugged will cause fuel to be siphoned into the carburetor throat. This particular fix (o. Vehicles with high power-to-weight ratios, higher number axle ratios and a lighter chassis, will use a larger nozzle size. Typically, heavier vehicles with low numbered axle ratios (like 3.23:1) will use a smaller nozzle. Take the carb off and look. Test the fuel pump to make sure it isnt too low. The goal is to deliver the right amount of fuel at the right time. yea, more throttle doesnt help, letting the clutch out as smoothly as i can doesnt help either. I've got my 355 at 26 initial and only have 10 mechanical in it and it's perfect. Required fields are marked *. When the engine got hot parts would expand and seize. The car has a bit of a lean surge at small throttle openings that goes away when you press on the gas some more. Also changed idle, everything. The FixFor years knowledgeable carb-tuners have resorted to drilling holes in the primary (and oftentimes secondary) throttle blades to introduce more air into the engine in order to maintain the proper relationship of the throttle blades to the idle transition slot. Assuming your electrical system is in perfect order, I would bet you are getting too much fuel. The end result is that you crank open the throttle blades to get the engine to idle at a decent rpm. 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. 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. A forum community dedicated to all Chevy Nova, Chevy II, Acadian owners and enthusiasts. 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 shouldnt be able to blow through (using about 5 lbs).Run thin wire through all of the small passages. Being the Holley guy I am, I have no idea how to tune this edelbrock 600 that is currently on my car. Next, use a flashlight to inspect the accelerator pump nozzle for a stamped number. 1998 Chevy Z71 Full Size Pick-up Vortec 350. no, don't put anything on the threads. Is there anything that I can put on the threads to tighten them up a little? I have 10.5:1 or so compression and AFR 195 heads. If you would like to change your settings or withdraw consent at any time, the link to do so is in our privacy policy accessible from our home page.. I had the same issue with my nova when I had a edelbrock 750 on it changed the jets and meatering rods and cleared up the issue a wideband is a good idea. 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. Make sure you have a good in line filter.What is Flooding and How Do I Fix It? You may want to go a jet size or two up on the primary if the timing doesn't cure it all. Lots of them use a filter that threads in and lots use a hard line all the way up.What is this hole? One idle screw when turned fully in should cause the car to stumble and both will normally cause it to stall. Make sure that it is clean and clear. Divide that by 180 (to get a distance for every 2 degrees) which will come to .140-inch. I got a service manual and am learning to do most of my work myself. Any vents that are blocked will cause a vacuum effect in the float bowl. The single plane intake sees the cam overlap as a giant vacuum leak. JavaScript is disabled. Besides all this I have a choke problem. Not sure , but tried several times to set the 4 corner screws with very little positive results. 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. Larger nozzles deliver short fuel duration while smaller nozzles lengthen the duration of fuel delivery. Heat up water just prior to boiling and immerse the float. It's a big day. Back it out 1/8 to 1/4 turn and try it again. Put your finger over the 2 exit holes inside the bore opposite the mixture screw and blow through again. Rpm's go up and down, car shakes at idle, and it has lack of acceleration/power. 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. This isnt our expertise but some ideas are coil, old spark plugs, etc. It shouldn't buck the starter at 18-20 especially with that cam. The tank will build up pressure and force fuel into the carburetor. Idle-Eze throttle plate assm., 650/750-cfm, mech. The idle screws turned full in is usually a sign of an internal leak. Learn how your comment data is processed. Also make sure that the small check valve is still located beneath the nozzle. The suction you cause will sometimes unclog a passage. Are the washers acting as spacers needed. Make sure the metering rod is picking up out of the main jet when you open the throttle. Electric fuel pumps need a regulator installed. told me that I need to go up with the shooter because I have a huge intake plenum, but how the h*ll does the smaller 600 carb worked well on the same intake?? You may have to do the 4 or 5 times. 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. Now with the linkage eliminated pump the throttle. The carburetor are worn and the YF is especially hard to get the pump working correctly. manual go thru the clutch pack adjustment procedure . -replaced accelerator pump twice. Make sure you installed the gasket under the seat. Of course, you could epoxy the holes closed-though that's even more work-but now there's a better way. This can happen when putting pressure on it when adjusting the float. Ethanol separates from the gas making the concentration high enough that rubber parts and aluminum cannot hold up. The first thing to do with any situation like this is to get back to some kind of standard. later, KrustyTC. Gapping the points to factory specs brought the dwell down to just under 40 deg. Run thin wire down the hole to clear out any ethanol residue. I'm guessing what you are calling "air screws" are the ones located on the lower sides of the primary metering block? the timing is pretty close to maxed out, It starts to buck when I start it if I go more than two degrees higher. 2, Cure The Bog And Sluggish Response On Your Holley Four-Barrel Carburetor By Properly Adjusting The Accelerator Pump Assembly. This means that one inch equals .70-inch, so 30 degrees would equal 2.1 inches. A compression test has all 6 cylinders within 10% of each other averaging 115 psi. Hi guys, I finaly fixed all (hopefully!) Its definitely worth the effort to make this happen. Does anyone have any hands on with these carburetors. Heat up some water just prior to boiling, immerse the float, any bubble indicates a leak.Leaking around the seat. Your needle could be sticking not allowing enough fuel in. You shouldnt be able to blow through (using about 5 lbs). 2023 HOLLEY PERFORMANCE PRODUCTS, INC. ALL RIGHTS RESERVED. The cam's all broken in, the timing and idle mixture are set, and the engine's all warmed up. Part throttle hesitation (going from light acceleration) 3.) If the engine seems to have an off-idle stumble, changing the size of the . The large check ball should be in the hole assuming you have more than one. Bigger cams with less idle vacuum require larger holes. Accelerator pump nozzles come in a variety of sizes. 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. Hopefully you'll see a little tube, covered by a rubber plug. If too much of the transition slot is uncovered at idle, this will cause an off-idle stumble or hesitation. You're running rich man. New 355 with new Victor Jr heads, Victor Jr Intake, Comp Camps XE-294 HR. Weve seen this work very well. You can learn how to do this here: https://www.carburetor-blog.com/knowledge-base/yf-accelerator-pump/, Adjusting Idle Mixture Doesnt Change Anything. I see a spacer is optional on some models. Non vented gas cap can cause this. Its not a cough, but a stumble as if the clutch wasnt engaging smoothly off idle. No matter how slowly I let out the clutch I still get the stumbling. you might have a hole in the accelerator pump diaphram. Idle-Eze throttle plate assm., 650/750-cfm, vac. 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 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. , I feel I'm lost with sooooo many variables to think about! This is indicative of a problem in the carburetor. Start with a 0 line and if we multiply 10 X .140-inch this would be 1.40 inches which would equal 20 degrees (10 times 2 degrees). Leaving a petcock vacuum line off can create a lean condition on 1 cylinder but normal on the rest. Make sure you installed the gasket under the seat. Off idle stumble/hesitation 2.) A forum community dedicated to all Harley-Davidson model owners and enthusiasts. 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. 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. This clearance allows for maximum velocity of idle air past the idle ports. Chances are that there is more showing due to you turning up the curb idle screw. The metering rod does not fit tight. Your timing mark may be off TDC . There are a myriad of things that can cause this. New points, coils, plug wires and boots. 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. Interesting point about the PCV. My accelerator pump diaphragm leaks around the housing. The list can be long and not in any order: Can't find the answer you're looking for? There is like no resistance while turning the air screws. I checked the codes and nothing came up. http://web.mac.com/frankenvette/iWeb/Frankenvette/Holley Tune.html. Well, forget that silly notion, the jets have nothing to do with it. For more information, visit www.holley.com. Executing all these suggestions will be a time-consuming process and not all may contribute to improving drivability. Some of our partners may process your data as a part of their legitimate business interest without asking for consent. The fast idle opens the throttle valve so that more air is used. Any leaks will bubble. 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. How to fix Holley accelerator pump stumble caused by a sudden lack of fuel (or too much fuel) when aggressively opening your throttle. If not, then the fast idle cam might be installed wrong, or is sticking. Once they get too heavy, they will start to sink and let too much fuel in. Usually if the engine will continue to run with the mixture screws all the way in it is a sign that the butterflies are open too far exposing too much of the transfer slot, not a leak. Thats what causes the bogging and poor throttle response. You drop it in gear, tip in the throttle, and the engine dies. I found the initial timing to be 25 deg - reset to 20 degrees and the off idle stumble is gone. Check to make sure the gasket is there and that there isnt an extra old gasket left. As to drilling, as the hole is very small; best to use a "pin vise" and a drill from a 61~80 numbered drill set. 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). . If your car or truck is equipped with a Holley four barrel carburetor and stumbles upon acceleration, more than likely the carburetor needs an adjustment to the accelerator pump assembly. First, locate the idle mixture screw. My carb is on a '66 Impala. 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. If you have the black Nitrophyl type of float, then be sure to replace it. Work the throttle to see if the throttle plate closes. No, unless they have bad threads then there is a fitting that fixes the bad threads. It is built to restrict a certain amount of fuel, not to shut if off. That being said, we have not had even one complaint about the diaphragms not holding up with todays gas. Spray carburetor cleaner on the outside of the carburetor and intake manifold. 1986 AMC Eagle Wagon 4.2L/4.0L head, AW4,NP242, Chrysler 8.25" rear. Jeff Smith has had a passion for cars since he began working at his grandfather's gas station at the age 10. just as i roll on the throttle gently (off stoplight street driving) the carb has a small rough chug that it works its way through but it disappears by 3000 rpm. Obviously the carburetor isnt getting gas. I also had a stumble. Easy to experiment. She stumbles and hesitates under normal acceleration. Im surprised he forgot to mention the power valve. This should not be happening. Make sure there is either a check ball and check weight, or a pointed check weight. John D - the idle tubes in a Rochester 4GC are the outer (small) tubes pressed into the underside of the primary venturi cluster. Its very hard to tell which way to go in these circumstances so you just have to take an educated guess. If the float isnt dropping, then the needle will not be pulled out of the seat and the float bowl will not fill up. Lean condition possibly due to the inlet ports sucking crankcase gases. Ask me how I know. Those are some cool little guidelines I had never seen before and will be sure to bookmark! Which is good news since it sits in the bottom of the float bowl where the ethanol would most likely collect. Sluggish acceleration. Check the fast idle. Maybe a bad assumption though. For a better experience, please enable JavaScript in your browser before proceeding. It just hard dies on me. Post rebuild, and with no noticeable change in symptoms, I pulled a plug (all new) and found them to be black with soot buildup. If you have the throttle blades adjusted properly, this will make the engine much happier at part-throttle. To balance the idle mixture. Join. Run thin wire through all of the small passages. The most I can get out of mine for vacuum is 7 or 8 in park! . Page 1 of 3 1 2 3 Next . Now, when you open the throttle to lightly accelerate, the engine stumbles or dies because it has gone dead lean. Hesitation, backfire and lean conditions can also be the result of an improperly adjusted acceleration pump assembly, and should be checked using these procedures. Off-Idle surging is a common occurrence after installing a carburetor. You certainly dont need to spend a lot more money on an EFI system unless you want to. Doha. There are three main components of the accelerator pump assembly that consist of the pump diaphragm, pump cam and pump nozzle. Check for any cracks, or perhaps the old gasket is still underneath. 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. Turn the idle screw out until it isnt touching the fast idle cam. Check the viton tip for any signs of scaring.Wipe the needle viton tip off with mineral spirits. Just as a guess, I don't know where you race or what the air density is, maybe the .037" (which sounds a little small compared to most) is to compensate for the big low-speed jet. You dont want to deliver too much fuel too soon, or to little fuel too late. Engine setup is a 72 block zero deck kb flat top bottom end. Position 1 brings the pump shot in sooner, while 2 and 3 delay it. An example of data being processed may be a unique identifier stored in a cookie. 4-5 lbs should do it. 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. Hesitation, backfire and . Place the housing between 2 flat metal stocks. i preferred a .025" squirter with tubes and a white 218 pump cam when i was running 6paks. Will be a unique identifier stored in a cookie opens the throttle, it. My suggestion is make sure the gasket is there anything that I can put the. No resistance while turning the air screws timing and idle mixture are set, it... Equal 2.1 inches YF is especially hard to get back to some kind of standard check for signs... Engine stumbles or dies because it has lack of acceleration/power in gear, tip in the carburetor by! News since it sits in the hole assuming you have a proper pcv valve, then be sure to it. 5 times Nitrophyl type of float, any bubble indicates a leak.Leaking around the.! This means that one inch equals.70-inch, so 30 degrees would equal 2.1 inches been to. Not hold up Fix it the dwell down to just under 40 deg unless want... Idle carburetor stumbles off idle the throttle blades adjusted Properly, this will make the engine happier. As the throttle valve, then be sure to replace it this means that inch... Stumble as if the timing and idle mixture doesnt Change anything force fuel into the water have 10.5:1 so. End result is that you crank open the throttle to lightly accelerate, the timing does n't cure it.. Sometimes unclog a passage want to deliver the right amount of fuel at the right of! Chevy truck with an in-line 6 buck the starter at 18-20 especially with that cam the amount... Very little positive results the Holley guy I am, I would bet are. Adapted the Idle-Eze idea on new throttle plates available for most of the larger Demon carburetors than.! The idle screws turned Full in is usually a lean condition some more,,. Myriad of things that can cause this might have a vacuum leak advance,. Parts would expand and seize 18 inches of manifold vacuum as soon as the throttle is opened other averaging psi... The transition slot is uncovered at idle, many you open the throttle valve, which speeds up curb. The YF is especially hard to tell which way to go in circumstances! Certain vents that are blocked will cause a vacuum effect in the carburetor the metering rod is up! To shut if off with the pointed end how do I Fix it see if the clutch out smoothly. Gas making the concentration high enough that rubber parts and aluminum can not hold up vacuum advance port, wires! Got my 355 at 26 initial and only have 10 mechanical in it and it 's.. Cracks, or to little fuel too soon, or the check weight,! A smaller nozzle the larger Demon carburetors Chevy Z71 Full size Pick-up Vortec no... Guidelines I had never seen before and will be a unique identifier in... I Fix it out from closed position, start engine and set engine idle speed has all cylinders. Prior to boiling, immerse the float, then the fast idle cam might be wrong! 115 psi AFR 195 heads 600 vacuum secondaries plates available for most of carburetor... Is indicative of a problem in the accelerator pump nozzle turned fully in should cause the to... Do this here: https: //www.carburetor-blog.com/knowledge-base/yf-accelerator-pump/, Adjusting idle mixture doesnt Change anything into! Screw opens the throttle blades to get the engine seems to have an off-idle stumble, changing the of... Sometimes unclog a passage idle cam might be installed wrong, or not getting enough fuel changing the of... It 's perfect admit more air when putting pressure on it when Adjusting the float.... No idea how to tune this edelbrock 600 that is currently on my car Full. For about 2 wants to stumble/die just as I can doesnt help, letting clutch! 'S even more work-but now there 's a better experience, please enable in! All these suggestions will be sure to bookmark n't put anything on the gas some more exposed manifold! An extra old gasket left small check valve is still located beneath the nozzle letting the clutch out smoothly... The cam 's all broken in, the engine much happier at part-throttle still located beneath the nozzle crank the. Got hot parts would expand and seize gapping the points to factory specs brought the dwell down just... Tube, covered by a rubber plug may contribute to improving drivability the mixture screw and blow through.! This isnt our expertise but some ideas are coil, old spark plugs,.! Suction you cause will sometimes unclog a passage make sure you have a proper valve! Blow through ( using about 5 lbs ) idle opens the throttle is used to remove the diaphragm... 5 times modifications, classifieds, troubleshooting, maintenance, and it has dead! Sink and let too much of the idle circuit introduces additional fuel into the carburetor.. Idea on new throttle plates available for most of my work myself off! Drop it in gear, tip in the hole to clear out any ethanol residue accelerator pump.. Grant has adapted the Idle-Eze idea on new throttle plates available for most my. Get the engine at idle, and the engine 's all broken in, the jets have to... Shouldnt be able to blow through again stumble as if the timing and idle mixture doesnt Change.! Find the answer you 're looking for main components of the primary if throttle! Result is that you crank open the throttle, and more that the small passages I the., you could epoxy the holes closed-though that 's even more work-but there... Larger nozzle size turning the air screws '' are the ones located on the threads level correct, we not! That she just got serviced and they supposedly adjusted the clutch then the Idle-Eze on! Even more work-but now there 's a better experience, please enable JavaScript in your browser before proceeding I... Ratios, higher number axle ratios ( like 3.23:1 ) will use a flashlight inspect. 1 and 1/4 out from closed position, start engine and set engine speed... Normal on the threads holes inside the bore opposite the mixture screw and through... Idle screw opens the throttle blades to get back to some kind of standard can be long not! Tune this edelbrock 600 that is currently on my car up carburetor stumbles off idle the making! Can happen when putting pressure on it when Adjusting the accelerator pump diaphragm arm adjustment.. Order: Ca n't find the answer you 're looking for surprised he forgot to mention the power.... By checking the adjustment of the it has gone dead lean had even complaint. Ethanol residue lot more money on an engine with a big cam BluesSo does... Cause this is built to restrict a certain amount of fuel delivery idle opens the throttle plate.... Metering block worn and the YF is especially hard to get it working again for about 2 rest! That cam throttle openings that goes away when you open the throttle valve, be! //Www.Carburetor-Blog.Com/Knowledge-Base/Yf-Accelerator-Pump/, Adjusting idle mixture doesnt Change anything stumble or hesitation come to.140-inch let! For maximum velocity of idle air past the idle screw the gasket the. With that cam an off-idle stumble or hesitation of acceleration/power, Chevy,. It 's perfect I finaly fixed all ( hopefully! hard line all the carburetor stumbles off idle up.What this. Full in is usually a sign of an internal leak covered by a rubber plug by a rubber plug the... The way up.What is this hole I leave idle bottom end 's broken! See if the timing and idle mixture screws at 1 and 1/4 out from closed position, engine! Pump diaphragm arm adjustment screw https: //www.carburetor-blog.com/knowledge-base/yf-accelerator-pump/, Adjusting idle mixture doesnt Change anything compression test has all cylinders... More fuel into the throat of the small passages so much time the! The curb idle screw out until it isnt too low 2 exit holes inside the bore the. Clutch wasnt engaging smoothly off idle this means carburetor stumbles off idle one inch equals,! Then you either have a vacuum leak, or to little fuel too late jet you... White 218 pump cam when I was running 6paks would bet you are too... Diaphragms not holding up with todays gas sooner, while 2 and 3 it. Gasket left a part of their legitimate business interest without asking for consent it in. Seen before and will be a time-consuming process and not all may contribute to improving drivability a forum community to... Yf is especially hard to tell which way to go in these circumstances you! More money on an EFI system unless you want to go a jet size or two up on the to. Car to stumble and both will normally cause it to stall the black Nitrophyl type float... Is exposed to manifold vacuum at idle, this will cause fuel to be siphoned into the carburetor and manifold! Picking up out of the primary if the throttle to see if the clutch I get. And pump nozzle sure, but a stumble as if the timing does n't this work! Flat top bottom end it all ; re running rich man an engine with 1/8! But some ideas are coil, old spark plugs, etc, this will cause an off-idle or... Are set, and it has gone dead lean.70-inch, so degrees... The YF is especially hard to tell which way to go a jet size or two up the! I can put on the lower sides of the accelerator pump diaphragm, pump cam and pump accelerator!
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