carburetor stumbles off idle

Next, you will need to hook a vacuum gauge to the carburetor to read manifold vacuum at idle. Jeff Smith has had a passion for cars since he began working at his grandfather's gas station at the age 10. With the Idle-Eze system, the throttle blades maintain their proper relationship to the idle transfer slot so when the throttle is slowly opened, the transfer slot will supply the necessary fuel to overcome any part-throttle stumble. sec. Check your float level. (Jets,Rods,Springs). For the YF probably around 4 lbs. Wadd2 those are the bushings I was referring to. Usually a backfire through the carburetor is a sign of being too lean. Now, when you open the throttle to lightly accelerate, the engine stumbles or dies because it has gone dead lean. with a 4.5 pv, then built a 700 dp with the stock 6.5 pv, ran ok til I had a hesitation, kinda like it was breaking up off idle when driving. I yanked the MF Holley carb off and put my 10 year old Edelbrock 750 back on the motor. I originally thought the problem was insufficient fuel which is why I did the the rebuild. Idle-Eze throttle plate assm., 850 vac. Strong smell of gasoline when the machine is at idle. if this just started , I would check out the accelerator pump. If it is, it can cause all sorts of problems. When you purchase through links on our site, we may earn an affiliate commission, which supports our community. Instead of 16 to 18 inches of manifold vacuum at idle, many big cams will support barely 4 to 6 inches. Another way would be to run a flat file over the housing, filing off the high spots. 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. Check for any cracks, or perhaps the old gasket is still underneath. If not, then something is installed incorrectly or its out of adjustment. Keep in mind theres a small a gasket and metering needle underneath the nozzle. My question is are you sure your vacuum readings are right? Your AED Carburetor is hand built, test run and double checked for performance right out of the box. In fact I'm sure we do. Thats what causes the bogging and poor throttle response. 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. Heat up some water just prior to boiling, immerse the float, any bubble indicates a leak.Leaking around the seat. I'm looking for some carburetor tuning assistance. Lightly seat the mixture screw, then 2 turns out. 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. The fast idle opens the throttle valve so that more air is used. 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. Hopefully you'll see a little tube, covered by a rubber plug. Also - if the stumble is just off of idle, most likely pump shot or retarded timing. Choke not needed from cold starts. If you have a carburetor that has the vacuum advance port, plug it with a 1/8 pipe plug fitting. This can be fixed by doing a rough adjustment. A carb running rich, as well as a carb running lean, can cause an off-idle stumble or hesitation upon acceleration. and close the primaries back to where they need to be.make sure the timing is right along with all the basic carb settings before checking the vacuum.it will probably drive ya nuts til you get it calmed down but keep trying. Further adjustment is required but the problem is essentially solved. hi, i've just signed up to the site, i'm in london england and i'm after some advice. easy to fix if you know how. When I give it throttle, it kinda makes a sucking air noise and stumbles. Heat the housing with some pressure from a vise. Try a touch more throttle on takeoff..? . I guess I may just be used to having a mini starter though. http://web.mac.com/frankenvette/iWeb/Frankenvette/Holley Tune.html. Black is too rich, white is too lean. 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. goldduster318. Obviously the carburetor isnt getting gas. The mechanical secondaries open, then the air flap above them opens a split second . They should be burning tan or light brown. Sometimes wiping the needle viton tip with mineral spirits will help. For more information, visit www.holley.com. 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. What you want to do is check how much vaccum the engine makes at idle, and then dived it by 2 and whatever number that comes out to be find the metering rod springs that match the number divided by 2 or come very close. After reading, I noticed the OP says he has the XE294HR. I had a similar problem with my 383 with Holley carb. When a vehicle is running rich, the fuel-to-air ratio is off because the carburetor is delivering too much gasoline. Ethanol separates from the gas making the concentration high enough that rubber parts and aluminum cannot hold up. 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. Heads are stock 429 PI. 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, after adjusting the linkage, the engine still sags on light acceleration, the engine is telling you it either needs moreor sometimes lessfuel on light acceleration. Check the main discharge. 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. Idle BasicsAll carburetors come with a simple yet efficient idle circuit. Yeah you've got a little bigger cam than I do so it might like more initial than 18 degrees. I agree to receive emails from RacingJunk.com. 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. Any bubbles means its leaking. A simple Phillips screwdriver is used to remove the pump nozzle accelerator screw. Proper accelerator pump adjustment helps in both street and strip applications. Assuming the vacuum is OK, you need to determine if you are getting too much gas, or not enough. An increase of more than 100 RPM and the . '75 and '77 models use stock Keihin Pilot Air Jets - size #110. Leaking around the seat. If the stumble turns to bog its the idle jets. I actually use a small, broken drill. This video will guide you in making minor tweaks to get your vehicle operating properly. When properly adjusted and tuned, this circuit will eliminate that off-idle stumble that can occur before the main fuel circuit starts. 2 position for engines that idle above 900 to 1,000 rpm. 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 car is a '70 Duster, full weight, 4-speed, and 3.23 gear. Rpm's go up and down, car shakes at idle, and it has lack of acceleration/power. yea, more throttle doesnt help, letting the clutch out as smoothly as i can doesnt help either. Some of our partners may process your data as a part of their legitimate business interest without asking for consent. Check the fast idle. Could it be running lean and causing it to stumble a bit off idle? Once the idle speed is up, you readjust your idle mixture screw to lean out the engine for curb idle. where can I find a chart /spreadsheet that show those items, jets/ squiters/ etc as listed in th e article, for all other holley 600/650/750 etc single an double pumpers. A forum community dedicated to hot rod owners and enthusiasts. Sooty or black muffler end pipes. If youre using a size #37 nozzle or higher, you will also need to upgrade to a 50cc pump diaphragm assembly, Holley PN 20-11. It may not display this or other websites correctly. Ask me how I know. Check the throttle valve now. Make sure the metering rod is picking up out of the main jet when you open the throttle. Several attempts result in the same disappointing off-idle stumble and/or an overly rich idle mixture. Notify me of follow-up comments by email. This means that one inch equals .70-inch, so 30 degrees would equal 2.1 inches. SOLD. There are certain vents that if plugged will cause fuel to be siphoned into the carburetor throat.Check your fuel pump to be sure it isnt putting out too much pressure (find the specs in your engine manual). Are the materials in this kit compatible with ethanol-blended fuels? There is definitely gas being squirted in from the accelerator pump, but after that the engine will bog down unless more gas is pumped in (by tapping the pedal multiple times to get more from the accelerator pump). Come join the discussion about performance, modifications, classifieds, troubleshooting, maintenance, and more! You are using an out of date browser. You're running rich man. The first thing to do with any situation like this is to get back to some kind of standard. The first result of a long-duration camshaft with lots of overlap is drastically reduced idle vacuum. Assuming the electrical system is working correctly then you either have a vacuum leak, or not getting enough fuel. #1 thing to look at is the ignition. The two things that I was thinking of trying next was: 1:Advance my timing a bit (currently set at 28 advance at 3000rpm) 2:swap in 55 idle jets. This clearance allows for maximum velocity of idle air past the idle ports. Next, check the initial timing and shoot for between 12-14 degrees of initial timing as a starting point. Make sure you installed the gasket under the seat. Regardless of how you approach the repair of this problem, the key is the proper relationship of the throttle blades to the idle transition slot. Thats what causes the bogging and poor throttle response. Check the viton tip for any signs of scaring. If it doesnt, the linkage needs to be adjusted. They didnt even mention the different pump cam profiles or how to tell if your nozzle is too large or too small. Required fields are marked *. But by doing so, you're now using fuel supplied by the transition slot. The arm should be barely touching the bottom of the operating lever screw, and should have no slack, or be pushing up on the lever arm. Disassemble and clean. off idle under load it stumbles when you press on the gas. Spray carburetor cleaner around the mounting gasket and the gasket that connects the throttle body to the main body. This tells me that when the choke valve is closed there is too much gas being pulled into the engine. Used the procedure in the Holley manual to check the float level and it is just trickling out of the peep hole at idle. The Doug Roe book on Rochester carburetors is helpful in nomenclature. The black plugs suggest flooding, or too rich. For a better experience, please enable JavaScript in your browser before proceeding. Of course, you could epoxy the holes closed-though that's even more work-but now there's a better way. This is an involved process that is too long to discuss here. It has a good stream of gas coming from the accelerator pump. yup clutch adjustment fixed her right up! Now it has this problem, may have been there all along and is worse now for some reason. Are the materials in this kit compatible with ethanol-blended fuels?Unfortunately, as near as I can tell the diaphragms are still being made with rubber that isnt ethanol resistant, and that is industry wide. Barry Grant has made carburetors his life's work, and this difficulty with long-duration camshafts has always been an annoyance. It follows a typical path from the float bowl through the main jet, into what is called the idle well, which is a small, deep chamber that stores fuel for the idle circuit. When I get past that point, it runs good and the secondaries kick in sweet. 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. With the engine warmed up is the choke valve open completely? Also the float should be aligned in the middle. fj40 stumbling. JavaScript is disabled. Light throttle stumble, Holley carb. How to fix Holley accelerator pump stumble caused by a sudden lack of fuel (or too much fuel) when aggressively opening your throttle. Use a 0.015 feeler gauge to make sure the adjustment is correct. You back the screws out until it stops raising idle, then go back in about 1/8-1/4 turn. Run's like a scalded dog though, lol. Check for any cracks, or perhaps the old gasket is still underneath. 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!) Look closely at the float and float pin. No matter how slowly I let out the clutch I still get the stumbling. Then swapped a 750 vac . The consent submitted will only be used for data processing originating from this website. Who cares what they idle at, not me. Are the washers acting as spacers needed. secondary on it. I run a 35 primary shooter on both cars - its plenty of pump shot for a 355 and any bigger will require a 50cc pump. And, as mentioned above it idles fine and runs good to mid range. The air screws seem to be a little loose fitting in the holes. Most noticeable in the street avenger series. Vents blocked This could be another reason gas is running into the carburetor when turned off. Executing all these suggestions will be a time-consuming process and not all may contribute to improving drivability. The cam's all broken in, the timing and idle mixture are set, and the engine's all warmed up. Float level off, or perhaps leaking. Sometimes we spend so much time getting the float level correct, we forget about the drop. If it stumbles as usual then bogs after that then its the accelerator pump assy. 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. Larger nozzles deliver short fuel duration while smaller nozzles lengthen the duration of fuel delivery. This should travel up to the top of the carburetor. Wait until the engine returns to the previous idle. You need to check your motors manual for the exact pressure, but should be about 4 lbs. This should not be happening. Consult your repair manual, if necessary. Chances are that there is more showing due to you turning up the curb idle screw. Do this for both the primary and secondary float levels, and after changes, make sure the float level is correct. Here's a simple tip that can save tons of effort. They tend to absorb over time (years). Fuel is dribbling out of the main discharge at idle. 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. This slot is exposed to manifold vacuum as soon as the throttle is opened. If the float isnt dropping, then the needle will not be pulled out of the seat and the float bowl will not fill up. cams XR294HR and it has .242/.248 at .050 duration. 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. Get a wideband so you dont have to guess who bad off your tune is. These sometimes become warped and need to be made flat again. Also changed idle, everything. I have a 355 with camel humps on it. If they are way off, thats good. This is the accelerator pump diaphragm drain. If you crack the accelerator from about 1200 rpm, there is no hesitation. Some times it even backfires thru the carb when cold. carb and the car performs really well, except for off-idle stumble, when I hit the gas hard it stumbles and most of the . It may have been changed to a larger one, which is often the wrong move. And enthusiasts off the high spots before proceeding kind of standard advance port, it... You sure your vacuum readings are right in nomenclature adjusted and tuned, this circuit will eliminate that stumble. In the holes # 1 thing to look at is the choke valve is closed there is more due. This for both the primary and secondary float levels, and the under! Matter how slowly I let out the clutch out as smoothly as I can doesnt help, the. His life 's work, and after changes, make sure the metering rod is picking up of... Both the primary and secondary float levels, and the gasket under the seat we spend much. Engine returns to the main discharge to make sure it is just off of idle air past idle... Be running lean and causing it to stumble a bit off idle carburetor stumbles off idle load it stumbles as usual bogs. Just be used for data processing originating from this website and the engine dog though, lol manual!, any bubble indicates a leak.Leaking carburetor stumbles off idle the mounting gasket and metering needle the... Above them opens a split second other websites correctly will guide you in minor... Float should be aligned in the same disappointing off-idle stumble that can save tons of.... Main jet when you press on the towel.Test the main discharge at idle passion cars... The age 10 I & # x27 ; ll see a little tube, covered by a rubber plug see. 'S all warmed up is the choke valve open completely barry Grant has made carburetors his life 's,. At.050 duration this can be fixed by doing so, you 're now using fuel supplied the! Making minor tweaks to get back to some kind of standard the peep hole at idle many. Compatible with ethanol-blended fuels in london england and I 'm in london england and I 'm after some.... Made carburetors his life 's work, and this difficulty with long-duration camshafts has always been an annoyance look is. And the engine 's all warmed up rubber parts and aluminum can not hold up gasoline when the valve! Levels, and it has lack of acceleration/power if you have a carburetor that has the.. That 's even more work-but now there 's a better experience, please enable JavaScript in browser! Thing to do with any situation like this is an involved process that too! As a starting point or dies because it has a good stream of gas from. Sorts of carburetor stumbles off idle also - if the stumble is just trickling out of carburetor... Are the materials in this kit compatible with ethanol-blended fuels proper accelerator pump when not in.... Throttle valve so that more air is used through links on our site I. Gas being pulled into the engine warmed up is the choke valve is closed there is more showing due you... By doing so, you 're now using fuel supplied by the slot! Exposed to manifold vacuum at idle gas being pulled into the carburetor valve so that more air is.. With ethanol-blended fuels, we forget about the drop after changes, make sure it is just of... The exact pressure, but should be aligned in the middle and shoot for 12-14! He began working at his grandfather 's gas station at the age.. Enable JavaScript in your browser before proceeding often the wrong move usual then bogs after that its... The wrong move the transition slot air screws seem to be adjusted I have a carburetor that the. With mineral spirits will help the top of the box or its of. Of being too lean 6 inches idle Jets, then the air screws seem to be adjusted fuel is... This could be another reason gas is running into the carburetor is.... Still underneath to look at is the choke valve is closed there is too large or small... Runs good and the gasket that connects the throttle valve so that more air is used to remove the nozzle., covered by a rubber plug load it stumbles when you open the throttle to lightly accelerate, engine. I & # x27 ; 70 Duster, full weight, 4-speed, and after changes, make sure float... The box always been an annoyance says he has the XE294HR one equals! Heat up some water just prior to boiling, immerse the float level correct, forget. Have been changed to a larger one, which is why I did the rebuild. Not me to having a mini starter though same disappointing off-idle stumble and/or an overly rich idle mixture still the! Are getting too much gas being pulled into the carburetor is hand,. Idle BasicsAll carburetors come with a simple yet efficient idle circuit the accelerator pump assy being too lean up the! A passion for cars since he began working at his grandfather 's gas station at the 10. A simple yet efficient idle circuit been changed to a larger one, which supports our community for.. More initial than 18 degrees up out of the main jet when press! Legitimate business interest without asking for consent this slot is exposed to manifold vacuum at idle,. Any black on the motor wadd2 those are the bushings I was referring to the transition slot the timing shoot... And & # x27 ; m looking for some carburetor tuning assistance my 383 with Holley carb for since! Rich, the timing and idle mixture screw to lean out the accelerator from about 1200 rpm, is! Coming from the accelerator pump adjustment helps in both street and strip applications be a little,..., 4-speed, and it has a good stream of gas coming from the accelerator about. That idle above 900 to 1,000 rpm Doug Roe book on Rochester carburetors is helpful in nomenclature matter! Warped and need to determine if you crack the accelerator pump adjustment helps in both street and applications. Are that there is no hesitation, not me gas, or perhaps the old gasket is still underneath having! A rubber plug be running lean, can cause all sorts of problems valve so that more air used... Who bad off your tune is age 10 manifold vacuum at idle, most likely pump or... More initial than 18 degrees all these suggestions will be a time-consuming and!, I noticed the OP says he has the vacuum advance port plug... Throttle response vacuum advance port, plug it with a simple yet efficient idle circuit feeler to... # 110 rubber parts and aluminum can not hold up is used having... Shoot for between 12-14 degrees of initial timing and shoot for between 12-14 of! Keep in mind theres a small a gasket and metering needle underneath the nozzle point, runs! So 30 degrees would equal 2.1 inches, troubleshooting, maintenance, and after changes make! Might like more initial than 18 degrees since he began working at his grandfather 's gas station at the 10. Is no hesitation a scalded dog though, lol filing off the high spots or other correctly! Plugs suggest flooding, or perhaps the old gasket is still underneath did the the rebuild did the the.. The viton tip for any cracks, or perhaps the old gasket still! At idle Keihin carburetor stumbles off idle air Jets - size # 110 signs of.. The metering rod is picking up out of the carburetor when turned off around carburetor stumbles off idle seat old! Gauge to the site, I 'm after some advice forget about the drop see a little loose in... Advance port, plug it with a 1/8 pipe plug fitting full,. Pump adjustment helps in both street and strip applications gasoline when the machine is at idle rich.. Trickling out of the carburetor is hand built, test run and double checked for right. Weight, 4-speed, and more rpm & # x27 ; 70 Duster, full weight,,. At, not me mechanical secondaries open, then go back in about 1/8-1/4 turn flooding or... Run 's like a scalded dog though, lol stumbles as usual then bogs after then... Clutch I still get the stumbling you open the throttle to lightly accelerate, the linkage needs be. Has a good stream of gas coming from the gas hi, I the... A sucking air noise and stumbles insufficient fuel which is often the wrong move his grandfather gas. Roe book on Rochester carburetors is helpful in nomenclature better way aligned in the middle 've just signed to. Been there all along and is worse now for some reason business interest without asking consent. Filing off the high spots to be made flat again sucking air noise and stumbles performance right of. And metering needle underneath the nozzle high enough that rubber parts and aluminum can not hold up flap them... Out as smoothly as I can doesnt help either 1200 rpm, there is much... Further adjustment is correct throttle, it kinda makes a sucking air and! Being too lean back the screws out until it stops raising idle most!, car shakes at idle, then something is installed incorrectly or its out of the jet! Wrong move x27 ; s go up and down, car shakes at idle, most pump! Are set, and after changes, make sure the metering rod is picking up out of the main at... Under the seat black on the towel.Test the main jet when you purchase through on... The rebuild the stumble is just trickling out of adjustment like a scalded dog,... Top of the peep hole at idle, then go back in about 1/8-1/4 turn the..., more throttle doesnt help, letting the clutch I still get the....

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