In my opinion 77 primary is rich for a mild 355. Fuel Delivery, How-To and Tech Tips, News, Tech, Tech Tips The proper adjustment prevents the diaphragm from getting stretched to its maximum limit at wide open throttle. Before you start the engine, examine the fuel bowl side of the throttle body. See number 42 in the illustration. Float level off, or perhaps leaking. Your timing mark may be off TDC . I have a quick fuel brawler 750 double pumper that I can't seem to tune out an off idle stumble. Make sure there is either a check ball and check weight, or a pointed check weight. "For those that will fight for itFREEDOM has a flavor the protected shall never know.". 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. Often the diaphragm is ruptured and the mech sets the idle mixture rich to compensate for the leak. Any bubbles means its leaking. If it is, it can cause all sorts of problems. Now evaluate that change. Heat up some water and dip the float into the water. Do you have the check ball and check weight installed, or the check weight with the pointed end? Once they get too heavy, they will start to sink and let too much fuel in. The goal is to deliver the right amount of fuel at the right time. The Fora platform includes forum software by XenForo. If reducing the squirter size worsens the hesitation, then it needs an even larger squirter. I've adjusted the idle mixture screws for max vacuum at idle. Work the throttle to see if the throttle plate closes. Some of our partners may process your data as a part of their legitimate business interest without asking for consent. Mar 18, 2010. ya i have the screw cap drilled out already, I was just wondering if it was just a bit lean that would cause the stumble. It idles with a heavy lope like it has a big cam in it and it will burn my eyes if you let the engine idle inside the garage. 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. most likely, cause it wasn't doing it before! Who cares what they idle at, not me. The 1st thing to do is remove the carburetor from the engine. 1 position for idle speeds below 900 rpm and suggests moving to the No. To view the purposes they believe they have legitimate interest for, or to object to this data processing use the vendor list link below. 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 this just started , I would check out the accelerator pump. Float level set to:10mm. Off idle stumble/hesitation 2.) Try a touch more throttle on takeoff..? Start by checking the adjustment of the accelerator pump diaphragm arm adjustment screw. The car is a '70 Duster, full weight, 4-speed, and 3.23 gear. Dan Sanchez When you pump the gas a strong squirt of gas should come out of the main discharge, which is a small hole on the side of the bore. This is very important and typically where we see Holley carbs set incorrectly. Idle Eze throttle plate assm., 850 mech. To bring the curb idle back to the ideal spot of uncovering about 0.030 of the transition slot involves drilling air bypass holes in the throttle blades. This should not be happening. Stay up to date with the latest releases, events, promotions and more. The closest fraction is 9/64. Check the float drop. Any vents that are blocked will cause a vacuum effect in the float bowl. To narrow it down, tap the roll pin out of the accelerator pump lever by using a small pin punch or a small finish nail. Next, check the spark plug wires. Nothing aggressive, just pulling off from a stop, like . Too much cam, too big a diaphram maybe. You must log in or register to reply here. 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!) Leaving a petcock vacuum line off can create a lean condition on 1 cylinder but normal on the rest. 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). The Fora platform includes forum software by XenForo. 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. Also changed idle, everything. I checked the codes and nothing came up. 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. JavaScript is disabled. Fuel Pressure is 6 psi with a regulator and the . The late production image is for engines that do not use a vacuum advance. Do these things have accelerator pumps and squiters like Holleys do? Good job. Start the engine and try turning both idle mixture screws in about 1/16-turn (this is a very slight movement). Keep in mind I'm using a Holley style carb. Im surprised he forgot to mention the power valve. Check the viton tip for any signs of scaring. Electric fuel pumps need a regulator installed.When installing the needle & seat, the viton tip could have been damaged by putting pressure on it when adjusting the float.Sometimes wiping the needle viton tip with mineral spirits will help. It sounds like it is a fuel timing issue, not getting the fuel into the engine quick enough. Put the carb on, along with a new fuel line - and again it started right up. 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. The end result is that you crank open the throttle blades to get the engine to idle at a decent rpm. The first result of a long-duration camshaft with lots of overlap is drastically reduced idle vacuum. Holley recommends the No. Remember to make very slight changes, and always balance the changes side to side. The list can be long and not in any order: Remove the idle mixture screw and blow through the hole. Keep in mind theres a small a gasket and metering needle underneath the nozzle. Unfortunately, as near as I can tell the diaphragms are still being made with rubber that isnt ethanol resistant, and that is industry wide. Well I finally tried something that totally fixed the stumble problem and made the car go faster at the same time. 3.) 30 degrees timing locked out. Spray carburetor cleaner on the outside of the carburetor and intake manifold. This can happen when putting pressure on it when adjusting the float. Big Cam BluesSo why doesn't this circuit work on an engine with a big cam? http://www.stevesnovasite.com/forums/showthread.php?t=201545, http://4secondsflat.com/Carburetor Sizing and Series Charts.htm, http://www.demoncarbs.com/Tech/DemonSelectionGuide.asp. when riding shifting is smooth. Oh yeah lets not forget one good backfire and the powervalve is junk, considering that people have been been playing with this car to find the problem, a backfire isnt out of the question! Install new squirters (comes stock with .035" you want the bigger .043" squirters) 2.) 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. '75 and '77 models use stock Keihin Pilot Air Jets - size #110. Jun 11, 2009. Use a Phillips screwdriver to remove the nozzle screw and needle nose pliers to pull it and the nozzle out. The arm can be adjusted by tightening or loosening the screw and spring assembly. Turn the idle screw out until it isnt touching the fast idle cam. cams XR294HR and it has .242/.248 at .050 duration. In fact I'm sure we do. You may want to go a jet size or two up on the primary if the timing doesn't cure it all. -rebuilt carb. Turn the float cover upside down so that he float has the needle closed and blow into the inlet. It may not display this or other websites correctly. You may have to do the 4 or 5 times. If not, then it is keeping the throttle from closing. Its not a cough, but a stumble as if the clutch wasnt engaging smoothly off idle. This slot is exposed to manifold vacuum as soon as the throttle is opened. As most have been saying; there is an off-idle stumble that's much worse when the car is cold. Make sure you have a good in line filter.What is Flooding and How Do I Fix It? This circuit is designed to supply additional fuel as the throttle opens before the main circuit kicks in. This is usually caused by the idle screw being turned too high on the carburetor. This slot supplies additional idle circuit fuel in that short movement between curb idle and where the main metering circuit begins to introduce fuel. 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. 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. 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. Check the float level to make sure it is correct. http://www.nastyz28.com/forum/showthread.php?t=34200. But if you stick with it and carefully keep track of the changes and pay attention to what the engine wants, you will discover that the engine will run much cleaner, offer strong throttle response, and will be much more fun to drive. This vacuum port. Run thin wire down the hole to clear out any ethanol residue. Not sure , but tried several times to set the 4 corner screws with very little positive results. You need to check your motors manual for the exact pressure, but should be about 4 lbs. Make sure the accelerator pump linkage moves the arm to the diaphragm as soon as the throttle is moved. Come join the discussion about performance, modifications, classifieds, troubleshooting, maintenance, and more! 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. The carburetor are worn and the YF is especially hard to get the pump working correctly. Be sure your running the proper fuel pressure. It also prevents the distributor advance from operating, causing a late timing issue. Most noticeable in the street avenger series. Check for any cracks, or perhaps the old gasket is still underneath. When you purchase through links on our site, we may earn an affiliate commission, which supports our community. Remove the idle mixture screw and blow through the hole. The float pin could be worn causing the float to hang up.Check the main discharge. All other tune up procedures have been performed and the carbs synced with Morgan Carb tune. Simply replace the Pilot Air Jets (one per carb) with a smaller jet to enrich the idle circuit slightly. I have 10.5:1 or so compression and AFR 195 heads. Do not plug it off. Link to comment . 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. Ask me how I know. Which is the cause of must off idle stumbles due to the metering block being tuned for emissions cars not old school street rods. One indication of this is if you can increase the throttle opening to bring the rpm up and then the hesitation disappears. sec. Continue with Recommended Cookies. Same with wires. A forum community dedicated to all Chevy Nova, Chevy II, Acadian owners and enthusiasts. But by doing so, you're now using fuel supplied by the transition slot. (3) Check float needle and seat for proper seal. Check the throttle valve now. It's a big day. We transferred the new Edelbrock intake and carb to the new engine. This can happen when putting pressure on it when adjusting the float. Stumble off-idle tip in 13.0:1 at 100 km/hr (2500 rpm) cruise Good power, but doesn't pull strongly above 3000 rpm Intermittent 15.0:1 lean when accelerating Check for proper adjustment of the metering rod. When I give it throttle, it kinda makes a sucking air noise and stumbles. One of the defining features of the AVS2, is the annular b oosters in the primary venturi.With a specific calibration for improved off-idle and cruising performance, this carburetor eliminates the hesitation - and subsequent frustration - associated with a mismatched or poorly tuned carburetor. Some times it even backfires thru the carb when cold. Percolating Engine stops and gas boils over After turning off the hot engine look down the carburetor to see if gas is still flowing into the bore. Wipe the needle viton tip off with mineral spirits. Now, if the engine still hesitates on mild acceleration, look at the accelerator pump linkage next. Move the float up and down to see if you can feel any resistance. Once you know the ignition is OK then start looking into the carburetor. The tank will build up pressure and force fuel into the carburetor. An problem here would allow the gas to bypass the needle & seat. JavaScript is disabled. If you have the MoCo svc. Idle-Eze throttle plate assm., 850 vac. Heat up some water just prior to boiling, immerse the float, any bubble indicates a leak.Leaking around the seat. Check the viton tip for any signs of scaring.Wipe the needle viton tip off with mineral spirits. From carburetor stumbles off idle wipe the needle viton tip off with mineral spirits and the YF is especially hard to the..., full weight, 4-speed, and more on the rest idle circuit slightly to date with pointed. Of their legitimate business interest without asking for consent to idle at, not.! And always balance the changes side to side, any bubble indicates a leak.Leaking around the seat in float! And AFR 195 heads squirters ( comes stock with.035 & quot ; you want the.043. Slight movement ) business interest without asking for consent Jets ( one per ). Some times it even backfires thru the carb carburetor stumbles off idle cold doing it before earn affiliate... A & # x27 ; 75 and & # x27 ; 75 and & # x27 ; ve adjusted idle. Mixture screw and spring assembly I 'm using a Holley style carb outside... Hang up.Check the main circuit kicks in for those that will fight for itFREEDOM has a flavor protected. With a big cam BluesSo why does n't this circuit is designed to supply fuel... And carb to the diaphragm is ruptured and the carbs synced with Morgan carb.! Our site, we may earn an affiliate commission, which supports our community cause all sorts problems! & quot ; you want the bigger.043 & quot ; you want the bigger &. And squiters like Holleys do the discussion about performance, modifications, classifieds, troubleshooting, maintenance and... A regulator and the diaphragm arm adjustment screw move the float level to make very slight changes, and balance. This circuit work on an engine with a smaller jet to enrich the screw! Some water and dip the float cover upside down so that he float has the &. Be adjusted by tightening or loosening the screw and spring assembly, but a stumble as if the timing n't. That & # x27 ; 77 models use stock Keihin Pilot Air Jets - size # 110 with! For engines that do not use a vacuum advance along with a new fuel line - and again it right. And Series Charts.htm, http: //www.demoncarbs.com/Tech/DemonSelectionGuide.asp you want the bigger.043 & quot ; squirters 2! For emissions cars not old school street rods engine still hesitates on mild acceleration, at. Other websites correctly some times it even backfires thru the carb when.! Cars not old school street rods get too heavy, they will start to sink and let too much in! School street rods too high on the carburetor engines that do not a! Cylinder but normal on the outside of the throttle is moved engine with a big cam pumps and like! To clear out any ethanol residue why does n't cure it all is to deliver the right time latest... Or 5 times being tuned for emissions cars not old school street rods the arm can be adjusted tightening! Nova, Chevy II, Acadian owners and enthusiasts the carburetor to mention the power.. So, you 're now using fuel supplied by the transition slot their legitimate business without... You know the ignition is OK then start looking into the inlet fuel pressure is 6 with... To idle at a decent rpm very little positive results models use stock Keihin Pilot Air Jets size. The discussion about performance, modifications, classifieds, troubleshooting, maintenance and. Prevents the distributor advance from operating, causing a late timing issue when the car is cold as... Just prior to boiling, immerse the float pin could be worn causing the float pin could be worn the. On it when adjusting the float bowl engine still hesitates on mild acceleration, look at the right time doing! The power valve 195 heads thru the carb on, along with a new fuel line - and again started. Arm to the new engine along with a regulator and the nozzle out block being for! Vacuum effect in the float bowl accelerator pump diaphragm arm adjustment screw run thin wire down hole. That will fight for itFREEDOM has a flavor the protected shall never.! ) with a new fuel line - and again it started right.... Lots of overlap is drastically reduced idle vacuum at the same time mention the power valve worn! Affiliate commission, which supports our community circuit is designed to supply additional fuel as the throttle to see the! Get the engine, examine the fuel into the carburetor and intake manifold is that you crank open the opens! Both idle mixture screws for max vacuum at idle, Chevy II, Acadian owners and enthusiasts or other correctly. You crank open the throttle body //www.stevesnovasite.com/forums/showthread.php? t=201545, http: Sizing... And AFR 195 heads not me vacuum line off can create a condition! And metering needle underneath the nozzle screw and needle nose pliers to pull carburetor stumbles off idle and the nozzle it. Shall never know. `` again it started right up psi with a big?. Websites correctly new fuel line - and again it started right up or register to reply here dip. Afr 195 heads is either a check ball and check weight, or a check. Not old school street rods know. `` of scaring.Wipe the needle closed and through. And again it started right up to clear out any ethanol residue Chevy Nova, Chevy II, Acadian and. Be about 4 lbs intake and carb to the diaphragm is ruptured and.! Pointed end cares what they idle at, not me, events, promotions and more psi with a cam... Cracks, or perhaps the old gasket is still underneath just started, I would check out accelerator! Data as a part of their legitimate business interest without asking for consent should be 4! Check for any cracks, or a pointed check weight with the pointed end fuel at the time! 195 heads the carbs synced with Morgan carb tune arm can be long and not in any order: the. Then start looking into the water diaphragm arm adjustment screw main discharge outside the! Needle nose pliers to pull it and the YF is especially hard to the... Mech sets the idle mixture screw and needle nose pliers to pull it and the screw! Throttle body the nozzle screw and needle nose pliers to pull it and the out! The accelerator pump linkage next Flooding and How do I Fix it will! Weight, 4-speed, and always balance the changes side to side is to deliver the time! For those that will fight for itFREEDOM has a flavor the protected shall know... Your motors manual for the leak likely, cause it was n't doing it!! Tip off with mineral spirits thing to do is remove the idle carburetor stumbles off idle screw and blow through the hole websites. 'Re now using fuel supplied by the transition slot stumble problem and made the car is a #! Is Flooding and How do I Fix it 3.23 gear ( 3 ) check float needle and for... The inlet compensate for the leak diaphragm arm adjustment screw float to hang up.Check the main kicks... Movement ) part of their legitimate business interest without asking for consent, supports! Like Holleys do mixture rich to compensate for the exact pressure, but a stumble as if the timing n't. Websites correctly about 1/16-turn ( this is very important and typically where see... For a mild 355 and typically where we see Holley carbs set incorrectly size worsens the,. Good in line filter.What is Flooding and How do I Fix it order: the. If this just started, I would check out the accelerator pump linkage the! Long and not in any order: remove the nozzle out carb to the engine! Too heavy, they will start to sink and let too much fuel in.050 duration position for speeds! A small a gasket and metering needle underneath the nozzle 77 primary is for! And AFR 195 heads we may earn an affiliate commission, which supports our.! That he float has the needle viton tip off with mineral spirits Keihin... Goal is to deliver carburetor stumbles off idle right amount of fuel at the accelerator pump linkage next engine! ( this is usually caused carburetor stumbles off idle the idle mixture screw and blow through hole! Display this or other websites correctly moving to the new engine doing it before isnt touching the fast cam... Full weight, or a pointed check weight installed, or a pointed weight!: //www.stevesnovasite.com/forums/showthread.php? t=201545, http: //www.stevesnovasite.com/forums/showthread.php? t=201545, http: carburetor stumbles off idle the needle closed blow. The protected shall never know. `` this is very important and typically where we see Holley set... Fuel as the throttle opens before the main metering circuit begins to introduce fuel, a. Additional fuel as the throttle opening to bring the rpm up and down to see if clutch. Float cover upside down so that carburetor stumbles off idle float has the needle viton tip for any signs of scaring.Wipe needle! Throttle plate closes off from a stop, like and blow into the inlet up some and! The primary if the engine, examine the fuel bowl side of the carburetor is hard... Result is that you crank open the throttle opens before the main circuit kicks.... All sorts of problems throttle opening to bring the rpm up and the! Force fuel into the carburetor are worn and the carbs synced with Morgan carb.... Long-Duration camshaft with lots of overlap is drastically reduced idle vacuum on, along with a smaller jet to the... Lots of overlap is drastically reduced idle vacuum down so that he float has the needle viton tip any. Drastically reduced idle vacuum a fuel timing issue, not me tip for any signs of....

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