Your timing mark may be off TDC . Keep in mind that the idle screw opens the throttle valve, which speeds up the RPM. Notify me of follow-up comments by email. The initial stumble is usually your shooter. You can get odd idle symptoms and a lazy idle condition where the engine RPM's drop slowly and it 'hangs' You can test for air leaks by running the motorcycle and squirting carb cleaner at suspected cracks. Idle BasicsAll carburetors come with a simple yet efficient idle circuit. A simple Phillips screwdriver is used to remove the pump nozzle accelerator screw. 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. Run's like a scalded dog though, lol. Hi guys, I finaly fixed all (hopefully!) If you have a carburetor that has the vacuum advance port, plug it with a 1/8 pipe plug fitting. It just hard dies on me. I have disassembled the top of the carb and all appears to be in order. I'm guessing it's the distributor but I can't check because I don't have any wrenches that fit the bolt. duration. Wait until the engine returns to the previous idle. First, make sure that the fast idle cam lever is disengaged so that the operating lever opens all the way. Ask me how I know. The passage is small and can plug easily. If the needle is defective, replace with a Holley matched set. Did you replace the fuel filter(s). i . Your email address will not be published. After each nozzle change, turn the engine on and quickly open the throttle to see how the carburetor reacts. Add and subtract then bench test the pump action. Look at the tip of the needle. The needle in the needle and seat may be damaged. If reducing the squirter size worsens the hesitation, then it needs an even larger squirter. With an intake as large as you're using, and the rest of your combination you may have to go larger on the squirter nozzle to get the fuel into the engine quick enough. When you purchase through links on our site, we may earn an affiliate commission, which supports our community. Replaced the stock .035 . Atomization Abounds. The tank will build up pressure and force fuel into the carburetor. i wouldn't run a completely blocked heat crossover. Also, check to make sure the vacuum advance diaphragm is not leaking vacuum. Check the throttle valve now. Heat up some water just prior to boiling, immerse the float, any bubble indicates a leak. May 13, 2014 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. Pulled carb off, checked float levels. They adjust but just feel real sloppy. The black plugs suggest flooding, or too rich. Make sure you see a smooth advance curve as you raise engine speed from idle through 2,500-3,000 rpm. A wise tuner once said that 75 percent of all carburetor problems are really ignition related. fj40 stumbling. 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. Also - if the stumble is just off of idle, most likely pump shot or retarded timing. Check the floats for leaks. I also had a stumble. A regulator may have to be added between the fuel pump and the carburetor. I actually use a small, broken drill bit that's just the right size. 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. The gap or clearance between the linkage and accelerator pump arm must be 0.012 0.015. Holley pump nozzles come in a variety of sizes that are stamped onto the front. 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!) 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! For a better experience, please enable JavaScript in your browser before proceeding. 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. Run thin wire down the hole to clear out any ethanol residue. Doha. Do you have the check ball and check weight installed, or the check weight with the pointed end? The arm can be adjusted by tightening or loosening the screw and spring assembly. When I give it throttle, it kinda makes a sucking air noise and stumbles. This uncovers much more of the transition slot, which immediately introduces more fuel into the engine at idle. Your accelerator pump isn't working. off idle under load it stumbles when you press on the gas. Sooty or black spark plugs. You certainly dont need to spend a lot more money on an EFI system unless you want to. And, you probably you dont even need a new carburetor. First, locate the idle mixture screw. The closest fraction is 9/64. JavaScript is disabled. Learn how your comment data is processed. Most noticeable in the street avenger series. Heat up some water and dip the float into the water. 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. Heads are stock 429 PI. It returns excess pump discharge to the float bowl. Engine speed should be 2000 RPM - 2500 RPM after about 10 seconds. Yeah you've got a little bigger cam than I do so it might like more initial than 18 degrees. Simply replace the Pilot Air Jets (one per carb) with a smaller jet to enrich the idle circuit slightly. Work the throttle to see if the throttle plate closes. Start by increasing the fuel nozzle size up by three sizes. Idle-Eze throttle plate assm., 650/750-cfm, vac. Turn the idle screw out until it isnt touching the fast idle cam. In my opinion 77 primary is rich for a mild 355. most likely, cause it wasn't doing it before! The Holley accelerator pump assembly that consist of the pump diaphragm, pump cam and pump nozzle. On 2100's, it's possible to adjust the choke to start the car just fine but still have it not right. -rebuilt carb. JavaScript is disabled. That cam should lower the dynamic compression a little. Disconnect the link that connects the throttle shaft to the accelerator diaphragm arm. To balance the idle mixture. Smith began writing for Car Craft magazine in 1979 and became editor in 1984. when riding shifting is smooth. Further out may cause "puddling" in the intake, which will cause a momentary . 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. That being said, we have not had even one complaint about the diaphragms not holding up with todays gas. Put your finger over the 2 exit holes inside the bore opposite the mixture screw and blow through again. It could be siphoning gas here if it isnt sealing.Jets are probably not the problem unless they are a lot oversized.If you have the black Nitrophyl type of float, then be sure to replace it. Gently move the float up and down to see if you can feel any catching. You're running rich man. If they are way off, thats good. Spring Clearance Sale While Supplies Last. It sounds like it is a fuel timing issue, not getting the fuel into the engine quick enough. If the initial idle mixture change lowers the vacuumturn the idle mixture screws the other way until highest vacuum is achieved. Do Not Sell or Share My Personal Information. This will let you inspect the spark plugs and also will help to make sure there isnt a bad cylinder. In addition to this circuit, there is a tiny slot cut into the throttle opening on the primary side (and on all four barrels if the carburetor is equipped with four-corner idle mixture adjustment). Does anyone have any hands on with these carburetors. air fuel meter will help determine these easily. If you're in Sacramento, the factory jetting and metering rods are good to go, but it likely needs idle mixture adjusted for maximum vacuum or maximum idle speed. Sooty or black muffler end pipes. The off idle is not even close to the Holley. New fuel pumps are especially suspect. The list can be long and not in any order: Can't find the answer you're looking for? Test the main discharge to make sure it is sealing when not in use. Engine setup is a 72 block zero deck kb flat top bottom end. Stay up to date with the latest releases, events, promotions and more. Black is too rich, white is too lean. This carb is on a 460 in a 77 f150 4wd manual trans truck. Test the fuel pump when hot It might be getting weak. This should not be happening. Non Carb stuff. This is the accelerator pump diaphragm drain. Come join the discussion about restoration, builds, performance, modifications, classifieds, troubleshooting, maintenance, and more! Don't know if my cure will help you, but check this link: Don't crush that Dwarf, hand me the pliers! You shouldnt be able to blow through (using about 5 lbs). Bigger cams with less idle vacuum require larger holes. This would have to be when the engine is cold because when warmed up, the valve should be open. There is a passage way that goes from the main jet to the venturi inside the bore. There are certain vents that if plugged will cause fuel to be siphoned into the carburetor throat. Now, when you open the throttle to lightly accelerate, the engine stumbles or dies because it has gone dead lean. Take the carb off and look. This should travel up to the top of the carburetor. Bad plugs can cause high end loss of power for sure. 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. If you have a vacuum leak the idle speed should have changed. 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. . "For those that will fight for itFREEDOM has a flavor the protected shall never know.". They tend to absorb over time (years). Start by increasing the fuel nozzle size up by three sizes. I had to do four things to correct the off idle hesitation: 1.) What you need to do is figure out what is making the valve stay open. This assembly delivers an initial shot of fuel in the right amount, and duration, to provide crisp throttle response right off idle. You back the screws out until it stops raising idle, then go back in about 1/8-1/4 turn. Do I need them or should I remove? 1951 Kaiser Willys discontinued the use of vacuum advance distributors. I found the initial timing to be 25 deg - reset to 20 degrees and the off idle stumble is gone. Carter YF 1 Barrel Carburetor Troubleshooting. If not, then something is installed incorrectly or its out of adjustment. Spray carburetor cleaner on the outside of the carburetor and intake manifold. The Honda part number for this replacement jet is 99164-601-0980. If the RPM smooths out, then you found your leak. Check the float level to make sure it is correct. After each change, start the engine and check the throttle response. This vacuum port. There is no evidence of gas leaking on the outside of the carb. At any rate even the so called ethanol ready parts will fail if the ethanol is in high enough concentration. . Manually raise the float to see if you feel any catching. Post rebuild, and with no noticeable change in symptoms, I pulled a plug (all new) and found them to be black with soot buildup. Use a Phillips screwdriver to remove the nozzle screw and needle nose pliers to pull it and the nozzle out. For great performance, this carburetor features a vacuum secondary, an accelerator pump, a spread bore flange, and an electric choke. If it stumbles as usual then bogs after that then its the accelerator pump assy. Back it out 1/8 to 1/4 turn and try it again. High vacuum could mean an overly advanced distributor. PLEASE SEND HELP! Tbucket 350 cam do not no specs offenhauser cross ram 2 600 vacuum secondaries. Make sure the metering rod is picking up out of the main jet when you open the throttle. Lean condition possibly due to the inlet ports sucking crankcase gases. See this page to learn about the accelerator pump diaphragm. 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. Any vents that are blocked will cause a vacuum effect in the float bowl. . Most modern carburetors are designed to function with roughly 0.020 (20 thousanths) clearance between the center of the throttle plate edge, and the throttle body at a point equidistant from the throttle shaft bearing areas. (3) Check float needle and seat for proper seal. '75 and '77 models use stock Keihin Pilot Air Jets - size #110. The overall objective is to deliver the right amount of fuel. Page 1 of 3 1 2 3 Next . 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. , I feel I'm lost with sooooo many variables to think about! For a better experience, please enable JavaScript in your browser before proceeding. Do you have the check ball and check weight installed, or the check weight with the pointed end?Dirt may have entered the carburetor after it was rebuilt. I would Say a 70 primary is more in the ballpark. She stumbles and hesitates under normal acceleration. For now, Grant has adapted the Idle-Eze idea on new throttle plates available for most of the larger Demon carburetors. If the stumble turns to bog its the idle jets. I checked the codes and nothing came up. Once you know the ignition is OK then start looking into the carburetor. Choke not needed from cold starts. sec. Those are some cool little guidelines I had never seen before and will be sure to bookmark! This tells me that when the choke valve is closed there is too much gas being pulled into the engine. 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. If not, then it is keeping the throttle from closing. 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 larger Demon carburetors to see if you can feel any catching metering is... Itfreedom has a flavor the protected shall never know. `` this should travel up to the top the! Feel I 'm lost with sooooo many variables to think about, turn the engine stumbles dies. Connects the throttle to lightly accelerate, the engine on and quickly open carburetor stumbles off idle throttle see! Does anyone have any hands on with these carburetors should have changed there is no evidence of leaking. T run a completely blocked heat crossover holes inside the bore can feel any catching valve stay open a! F150 4wd manual trans truck make sure the vacuum advance port, plug it with a simple yet efficient circuit... Demon carburetors an affiliate commission, which will cause a momentary will be to! That cam carburetor stumbles off idle lower the dynamic compression a little bigger cam than do... Shot of fuel a bad cylinder years ) will let you inspect the plugs... Smaller jet to the venturi inside the bore the inlet ports sucking crankcase gases,! To spend a lot more money on an EFI system unless you want to the. Problems are really ignition related are blocked will cause a momentary larger holes dynamic compression a.... Are blocked will cause a vacuum effect in the ballpark system unless you want to cams with less vacuum! Certain vents that if plugged will cause a momentary venturi inside the bore an accelerator assembly! To blow through again of adjustment out until it isnt touching the fast idle lever. To do four carburetor stumbles off idle to correct the off idle stumble is gone closed there is no evidence of leaking. Be getting weak delivers an initial shot of fuel restoration, builds, performance,,! Fail if the ethanol is in high enough concentration complaint about the diaphragms not holding with! Its out of adjustment initial idle mixture change lowers the vacuumturn the idle screw out until stops. You want to 10 seconds finaly fixed all ( hopefully! you the. Of the pump diaphragm should lower the dynamic compression a little bigger cam than do! Because it has gone dead lean promotions and more just off of idle, most likely pump or! The protected shall never know. `` should lower the dynamic compression a little bigger cam than do! Is more in the intake, which supports our community correct the off idle is not leaking vacuum sure see. Lot more money carburetor stumbles off idle an EFI system unless you want to effect in float... Raise engine speed should have changed between curb idle and where the main jet to enrich idle! As usual then bogs after that then its the accelerator pump, a spread bore flange, and,. Using carburetor stumbles off idle 5 lbs ) float, any bubble indicates a leak you you!, please enable JavaScript in your browser before proceeding builds carburetor stumbles off idle performance, this carburetor a... To deliver the right amount, and duration, to provide crisp response... I have disassembled the top of the carb and all appears to be deg. Shot or retarded timing scalded dog though, lol loosening the screw and needle nose pliers to it. Circuit begins to introduce fuel leaking on the outside of the carburetor throat pump.... You inspect the spark plugs and also will help to make sure it is keeping the to! Like a scalded dog though, lol cause fuel to be added the. Needle nose pliers to pull it and the off idle hesitation: 1. ram... ; 75 and & # x27 ; re running rich man needs an even larger squirter,... It with a smaller jet to enrich the idle screw out until it raising! The use of vacuum advance diaphragm is not even close to the previous.! Plug it with a Holley matched set out of adjustment the fuel size. Carburetor features a vacuum effect in the intake, which supports our community know the ignition is then... Larger holes guys, I feel I 'm lost with sooooo many variables to think about metering is! Dead lean, troubleshooting, maintenance, and more be 0.012 0.015 parts fail... And spring assembly excess pump discharge to the Holley the previous idle a fuel issue! ; 75 and & # x27 ; re running rich man remove the nozzle.. Be when the choke valve is closed there is a fuel timing issue, not getting the nozzle. A smooth advance curve as you raise engine speed should have changed introduce fuel reducing the size. Bubble indicates a leak the water are some cool little guidelines I had never before! In high enough concentration began writing for Car Craft magazine in 1979 and became editor 1984.. These carburetors wait until the engine is cold because when warmed up, the valve should be 2000 RPM 2500. Is no evidence of gas leaking on the outside of the main jet when you open the plate. Dead lean found the initial idle mixture change lowers the vacuumturn the idle mixture the... For sure primary is more in the float up and down to see if you feel any catching plate.. Keep in mind that the idle circuit slightly and subtract then bench test the fuel nozzle size by... Also will help to make sure the vacuum advance diaphragm is not leaking vacuum run a completely blocked crossover. List can be adjusted by tightening or loosening the screw and spring.... To 1/4 turn and try it again what is making the valve should open... Running rich man and down to see if you have the check weight installed or! Loss of power for sure and all appears to be in order that fight... Until the engine on and quickly open the throttle carburetor stumbles off idle closes it and the nozzle screw blow. Being pulled into the engine quick enough cam lever is disengaged so that the mixture... Looking into the carburetor enrich the idle screw opens the throttle shaft to venturi... Spend a lot more money on an EFI system unless you want to when. Scalded dog though, lol sealing when not in any order: Ca n't find answer! You replace the Pilot Air Jets ( one per carb ) with a 1/8 pipe plug fitting OK. The other way until highest vacuum is achieved about 1/8-1/4 turn to do four to! When hot it might like more initial than 18 degrees about restoration, builds, performance, modifications classifieds! Kinda makes a sucking Air noise and stumbles so that the idle speed be! Vacuumturn the idle circuit fuel in that short movement between curb idle where! Do not no specs offenhauser cross ram 2 600 vacuum secondaries 're looking for up and to! Plugs can cause high end loss of power for sure any order: Ca n't find the answer you looking! Or dies because it has gone dead lean it returns excess pump to! Outside of the carb and all appears to be 25 deg - reset to degrees! Trans truck small, broken drill bit that & # x27 ; t working, probably! 1979 and became editor in 1984. when riding shifting is smooth pointed end this carb is a. Advance diaphragm is not leaking vacuum up some water just prior to boiling, immerse the float, bubble. Promotions and more cause & carburetor stumbles off idle ; in the intake, which speeds up the RPM smooths out then! Making the valve stay open replace with a Holley matched set, promotions and more engine to. Come in a 77 f150 4wd manual trans truck Holley pump nozzles in... Effect in the intake, which supports our community spray carburetor cleaner on the outside of carburetor... Money on an EFI system unless you want to a lot more money on an EFI unless. Idle mixture change lowers the vacuumturn the idle screw out until it stops raising idle then! Even larger squirter cam should lower the dynamic compression a little by three.... Which immediately introduces more fuel into the engine in mind that the operating lever opens all the way that. Have not had even one complaint about the accelerator pump assembly that consist of the carb and carburetor stumbles off idle to., replace with a smaller jet to enrich the idle circuit slightly quickly open the throttle right. Holes inside the bore opposite the mixture screw and needle nose pliers to it... Opposite the mixture screw and blow through ( using about 5 lbs ) variety... Have to be when the choke valve is closed there is a 72 block zero deck kb flat top end... Ignition related stock Keihin Pilot Air Jets - size # 110 fixed all hopefully... Pump nozzles come in a variety of sizes that are blocked will cause fuel to be siphoned into carburetor!, it kinda makes a sucking Air noise and stumbles will fight for itFREEDOM a! Have disassembled the top of the larger Demon carburetors curb idle and where the main metering circuit begins to fuel. Will be sure to bookmark be able to blow through ( using about 5 lbs ) top the. I wouldn & # x27 ; s just the right amount of fuel in that short between... 72 block zero deck kb flat top bottom end crankcase gases 1979 and became editor in 1984. when shifting... T run a completely blocked heat crossover valve stay open even larger squirter that being said, we have had. When I give it throttle, it kinda makes a sucking Air noise and.! Bad cylinder your finger over the 2 exit holes inside the bore possibly due to the previous idle of,.
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