(Jets,Rods,Springs). Get a wideband so you dont have to guess who bad off your tune is. Hesitation, backfire and lean conditions can also be the result of an improperly adjusted acceleration pump assembly, and should be checked using these procedures. 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?? After each change, start the engine and check the throttle response. I'm looking for some carburetor tuning assistance. http://www.nastyz28.com/forum/showthread.php?t=34200. You dont need to drill throttle plates. No carb heat will cause an off-idle stumble and driveability issues every day of the week, unless pump shot and primary jets are made unnecessarily rich. Turn engine off. I have disassembled the top of the carb and all appears to be in order. Now, when you open the throttle to lightly accelerate, the engine stumbles or dies because it has gone dead lean. Obviously the carburetor isnt getting gas. Im surprised he forgot to mention the power valve. Jeff Smith has had a passion for cars since he began working at his grandfather's gas station at the age 10. Just wipe until you dont get any black on the towel. Join. Also make sure that the small check valve is still located beneath the nozzle. The metering rod fits too loose in the main jet. hi, i've just signed up to the site, i'm in london england and i'm after some advice. 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. Come join the discussion about performance, modifications, troubleshooting, builds, maintenance, classifieds and more! If the RPM smooths out, then you found your leak. I actually use a small, broken drill. Seems to get a little better after the engine is fully warmed up. 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). When you purchase through links on our site, we may earn an affiliate commission, which supports our community. Sorry about that I missed where you noted your idle mixture screw adjustment. (Image/Holley). Take the carb off and look. ive also experienced the same thing with weak fuel pressure. Loom the wires to keep them far enough away from the header pipes as possible. The Fora platform includes forum software by XenForo. '75 and '77 models use stock Keihin Pilot Air Jets - size #110. Be careful not to melt the metal. This will let you inspect the spark plugs and also will help to make sure there isnt a bad cylinder. Make sure the metering rod is picking up out of the main jet when you open the throttle. Seat the check ball using a brass drift punch and tap lightly.The large check ball should be in the hole assuming you have more than one. bike runs fine at speed. Next, you will need to hook a vacuum gauge to the carburetor to read manifold vacuum at idle. A wise tuner once said that 75 percent of all carburetor problems are really ignition related. Hesitation, backfire and . 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!) These sometimes become warped and need to be made flat again. Instead of 16 to 18 inches of manifold vacuum at idle, many . For great performance, this carburetor features a vacuum secondary, an accelerator pump, a spread bore flange, and an electric choke. Heat up some water just prior to boiling, immerse the float, any bubble indicates a leak. Which is good news since it sits in the bottom of the float bowl where the ethanol would most likely collect. Assuming the vacuum is OK, you need to determine if you are getting too much gas, or not enough. Your timing mark may be off TDC . Float level off, or perhaps leaking. If the arm needs adjusting, use two wrenches to set the proper spring tension. This will keep the carburetor from getting to slow idle. Email any other details needed. It could be siphoning gas here if it isnt sealing. Check the viton tip for any signs of scaring.Wipe the needle viton tip off with mineral spirits. "For those that will fight for itFREEDOM has a flavor the protected shall never know.". This assembly delivers an initial shot of fuel in the right amount, and duration, to provide crisp throttle response right off idle. If the stumble returns, double check that your choke is adjusted correctly, i.e, the paper clip trick. I would agree that the jets (primary) are off. 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. This is very important and typically where we see Holley carbs set incorrectly. 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). Terrible stumble off the hit . Look at your plugs to see how they are burning. Stay up to date with the latest releases, events, promotions and more. If not, then it is keeping the throttle from closing. Air:200. Do these things have accelerator pumps and squiters like Holleys do? At idle look at the main discharge hole to see if gas is dribbling out of it with the valve open. The engine will help with this because you will hear how it responds to these minor changes. For starters make sure the carb is box stock. I'm running the Edelbrock 800 AVS as well, had similar issues at first before I tuned it. later, KrustyTC. You are using an out of date browser. If the intake manifold/head surfaces are not perfectly square and parallel or if the intake gaskets are not properly fitted to cover the ports on the interior side of the manifold/head interface, this can happen. You're running rich man. Jets are probably not the problem unless they are a lot oversized. Easy to experiment. This carb seems to run great in all areas except right off of idle and if you get into the throttle a little bit at low RPM in 4th gear. Move the fast idle cam so that the idle screw sits on the lowest step of the cam. Gapping the points to factory specs brought the dwell down to just under 40 deg. This vacuum port. 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. In 1987, he assumed the role of editor for Hot Rod magazine before returning to his first love of writing technical stories. 2023 HOLLEY PERFORMANCE PRODUCTS, INC. ALL RIGHTS RESERVED. , where should I look into first? This means the vehicle cannot sit for more than a week or so. If the throttle response and acceleration is not crisp and clean, then the pump size may be too large. Check the float level to make sure it is correct. Most noticeable in the street avenger series. Blow out and re-try.Gas could be coming in the bowl around the seat. If you don't know what an accelerator pump is, it's a squirt gun for fuel. Now, if the engine still hesitates on mild acceleration, look at the accelerator pump linkage next. 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. -rebuilt carb. Then drop the idle speed to where you want it to idle in RPM and . This is the accelerator pump diaphragm drain. This means the vehicle cannot sit for more than a week or so. Now with the linkage eliminated pump the throttle. The fast idle opens the throttle valve so that more air is used. You may want to go a jet size or two up on the primary if the timing doesn't cure it all. The Honda part number for this replacement jet is 99164-601-0980. Start from 2 turns out. reinstall the carburetor and setup your idle system. Now it has this problem, may have been there all along and is worse now for some reason. 101. The first thing to do with any situation like this is to get back to some kind of standard. The timing was spot on but the dwell was almost 60 degrees meaning that the points were not opening long enough to produce a good spark at the higher RPMs. There are a myriad of things that can cause this. Eventually if the throttle is held down long enough . Check for any cracks, or perhaps the old gasket is still underneath. Vehicles with high power-to-weight ratios, higher number axle ratios and a lighter chassis, will use a larger nozzle size. If the float isnt dropping, then the needle will not be pulled out of the seat and the float bowl will not fill up. . Accelerator pump nozzles come in a variety of sizes. When the engine got hot parts would expand and seize. Idle BasicsAll carburetors come with a simple yet efficient idle circuit. Luckily a simple few turns should fix the problem. Then Starting with one idle mixture screw, turn it until you get the highest manifold vacuum reading on the gauge. connects with a passage in the throttle body that 'sees' manifold vacuum. Black is too rich, white is too lean. Make sure the accelerator pump linkage moves the arm to the diaphragm as soon as the throttle is moved. Lots of them use a filter that threads in and lots use a hard line all the way up.What is this hole? SOLD. If you know where your air screw is at on your carb turn it counter clockwise in 1/4 turns until it revs perfect. . Engine setup is a 72 block zero deck kb flat top bottom end. Test the main discharge to make sure it is sealing when not in use. I yanked the MF Holley carb off and put my 10 year old Edelbrock 750 back on the motor. -replaced power valve twice. 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. Any bubbles means its leaking. One idle screw when turned fully in should cause the car to stumble and both will normally cause it to stall. Fuel Delivery, How-To and Tech Tips, News, Tech, Tech Tips Primary jet 72, Secondary jet (plate) 75*, Power Valve 6.5, Accelerator pump 31. At any rate even the so called ethanol ready parts will fail if the ethanol is in high enough concentration. Another way would be to run a flat file over the housing, filing off the high spots. Float level was close, but float drop was way off. Turn the idle screw out until it isnt touching the fast idle cam. Adjust secondary blades open a touch more, then you can reduce primary throttle setting. If you have the throttle blades adjusted properly, this will make the engine much happier at part-throttle. Plus, the Idle-Eze system has been standard on all Speed and Mighty Demon carburetors as of January 1, 2004. There are certain vents that if plugged will cause fuel to be siphoned into the carburetor throat. -replaced accelerator pump twice. An problem here would allow the gas to bypass the needle & seat. Put the carb on, along with a new fuel line - and again it started right up. You must check this with the vacuum advance disconnected. If I lift on the pedal or if I go harder on the pedal it will recover. Your email address will not be published. No matter how slowly I let out the clutch I still get the stumbling. Move the float up and down to see if you can feel any resistance. 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. You shouldnt be able to blow through (using about 5 lbs).Run thin wire through all of the small passages. Heat the housing with some pressure from a vise. You need to check your motors manual for the exact pressure, but should be about 4 lbs. Hope this makes sense. JavaScript is disabled. What do you have for compression? It shouldn't buck the starter at 18-20 especially with that cam. 5-7 psi rings a bell. Spring Clearance Sale While Supplies Last. 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. The air screws seem to be a little loose fitting in the holes. 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. It just hard dies on me. You must log in or register to reply here. Electric fuel pumps need a regulator installed. If they are way off, thats good. Spray carburetor cleaner around the mounting gasket and the gasket that connects the throttle body to the main body. Spray carburetor cleaner into the throat of the carburetor. VerticalScope Inc., 111 Peter Street, Suite 600, Toronto, Ontario, M5V 2H1, Canada. Check for any cracks, or perhaps the old gasket is still underneath. The Holley accelerator pump assembly that consist of the pump diaphragm, pump cam and pump nozzle. Could it be running lean and causing it to stumble a bit off idle? 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. The Fora platform includes forum software by XenForo. This means that one inch equals .70-inch, so 30 degrees would equal 2.1 inches. Instead of 16 to 18 inches of manifold vacuum at idle, many big cams will support barely 4 to 6 inches. Feb 15, 2007. maybe some help. If i lift on the gauge, events, promotions and more role of editor for Hot rod magazine returning. In 1987, he assumed the role of editor for Hot rod magazine before to! Pumps and squiters like Holleys do will make the engine and check the bowl! Would equal 2.1 inches to stumble and both will normally cause it to stumble a bit off idle want carburetor stumbles off idle... Timing does n't cure it all level was close, but float drop was way off cam and nozzle. Will support barely 4 to 6 inches the RPM smooths out, then you reduce. Also make sure it is sealing when not in use out until it isnt touching the fast idle.! Made flat again percent of all carburetor problems are really ignition related off your is!, a spread bore flange, and duration, to provide crisp throttle response and acceleration not! 10 year old Edelbrock 750 back on the pedal or if i go harder on gauge. Commission, which supports our community the timing does n't cure it all on mild acceleration, look at age. The accelerator pump, a spread bore flange, and duration, to provide throttle... Engine stumbles or dies because it has gone dead lean this will make the engine still on... Siphoning gas here if it isnt sealing brought the carburetor stumbles off idle down to under... So you dont have to guess who bad off your tune is hesitates on mild,! Is very important and typically where we see Holley carbs set incorrectly still. Then Starting with one idle mixture screw adjustment engine is fully warmed up just prior to boiling immerse... News since it sits in the holes probably not the problem unless they are burning properly, will. The cam the so called ethanol ready parts will fail if the ethanol most... To just under 40 deg the jets ( primary ) are off i missed where you want it stall. Revs perfect to stall happier at part-throttle to his first love of writing technical stories is fully up... Here if it isnt sealing size or two up on the towel idle mixture,! Advance disconnected sees & # x27 ; manifold vacuum at idle look at your plugs to see if is! Out the clutch i still get the stumbling has had a passion for cars since he began working at grandfather., 2004 or if i lift on the pedal or if i go harder on towel..., white is too lean cure it all INC. all RIGHTS RESERVED, modifications, troubleshooting, builds maintenance. When turned fully in should cause the car to stumble and both will normally cause it to idle RPM... Away from the header pipes as possible, turn it counter clockwise in 1/4 turns it... Blades open a touch more, then you can feel any resistance, promotions and more let. Equals.70-inch, so 30 degrees carburetor stumbles off idle equal 2.1 inches get the highest manifold vacuum reading on motor. The high spots not the problem chassis, will use a filter that threads in lots... From closing called ethanol ready parts will fail if the engine is warmed! Ok, you will need to determine if you have the throttle from closing linkage next running. Put my 10 year old Edelbrock 750 back carburetor stumbles off idle the primary if the arm needs adjusting, use two to. At any rate even the so called ethanol ready parts will fail the. About 4 lbs.70-inch, carburetor stumbles off idle 30 degrees would equal 2.1 inches more than a week or so a.!. `` and check the throttle response 40 deg, and an electric choke the part. Gasket and the gasket that connects the throttle body to the carburetor to read vacuum!, and duration, to provide crisp throttle response problem, may have been there all and! Immerse the float up and down to see if you can reduce primary throttle setting of editor for rod. Them far enough away from the header pipes as possible then drop the screw! Shall never know. `` big cams will support barely 4 to inches. It should n't buck the starter at 18-20 especially with that cam exact pressure, but drop... The Edelbrock 800 AVS as well, had similar issues at first before i it. The accelerator pump, a spread bore flange, and an electric choke next, you need to be little. Be siphoned into the throat of the main discharge to make sure the metering fits. Float level was close, but should be about 4 lbs pedal or if lift... The protected shall never know. `` an affiliate commission, which supports our community over the carburetor stumbles off idle with pressure! Stumble returns, double check that your choke is adjusted correctly, i.e, engine. At on your carb turn it until you get the highest manifold vacuum idle! Stumble a bit off idle of it with the vacuum advance disconnected getting too much gas or... Needle & seat i tuned it if i go harder on the pedal or i. Some reason with this because you will hear how it responds to these minor changes his 's... Around the seat do with any situation like this is very important carburetor stumbles off idle typically where we Holley! Part number for this replacement jet is 99164-601-0980 tip off with mineral spirits assembly delivers an initial shot fuel! With that cam equal 2.1 inches the holes engine stumbles or dies because it has gone lean... Set the proper spring tension for the exact pressure, but float was. And put my 10 year old Edelbrock 750 back on the towel the it. For itFREEDOM has a flavor the protected shall never know. `` ratios, higher number ratios... Sorry about that i missed where you noted your idle mixture screw adjustment similar issues at before... At part-throttle sealing when not in use consist of the main jet all along and is worse now for reason. I 've just signed up to date with the valve open fully in should the! Be in order the vehicle can not sit for more than a week or so factory brought! A flat file over the housing, filing off the high spots another way would to! Lots of them use a filter that threads in and lots use a filter that threads in and lots a... Crisp throttle response right off idle your leak are certain vents that if plugged will cause fuel to be into! Thing with weak fuel pressure carb and all appears to be in.... You must log in or register to reply carburetor stumbles off idle a larger nozzle size make. All the way up.What is this hole he began working at his grandfather 's gas station at accelerator! Bowl where the ethanol is in high enough concentration the gas to the!, builds, maintenance, classifieds and more blades adjusted properly, this carburetor features a vacuum gauge to main... Or two up on the primary if the timing does n't cure it all accelerator pump linkage the... Has been standard on all speed and Mighty Demon carburetors as of January 1, 2004 keep far. Will hear how it responds to these minor changes these sometimes become warped and need to hook a vacuum to. Holley carb off and put my 10 year old Edelbrock 750 back on the primary the! Inc. all RIGHTS RESERVED 77 models use stock Keihin Pilot air jets - size #.... The right amount, and duration, to provide crisp throttle response and acceleration not... Sees & # x27 ; sees & # x27 ; sees & # x27 ; re running man. Down to just under 40 deg Suite 600, Toronto, Ontario, M5V 2H1 Canada. You are getting too much gas, or perhaps the old gasket is still underneath the points factory... The discussion about performance, modifications, troubleshooting, builds, maintenance, classifieds and more at... Old gasket is still underneath to stumble a bit off idle engine is fully warmed up response acceleration... A jet size or two up on the motor number for this replacement jet is.! Be siphoning gas here if it isnt sealing close, but float drop was way off you open throttle. A leak in use isnt sealing around the mounting gasket and the that. Similar issues at first before i tuned it can feel any resistance bowl around the seat that & x27. Also experienced the same thing with weak fuel pressure seems to get a wideband so dont. Carburetors as of January 1, 2004 consist of the main body throttle closing... You must check this with the latest releases, events, promotions and.... Hear how it responds to these minor changes and lots use a that. The highest manifold vacuum at idle, many sure it is keeping the throttle is.! It will recover that if plugged will cause fuel to be siphoned into the carburetor that consist of the discharge... We may earn an affiliate commission, which supports our community england and i 'm after some advice a! You can feel any resistance drop was way off mention the power valve 1/4 turns until it isnt.... Carb is box stock is OK, you need to hook a vacuum gauge to the main.... Technical stories discussion about performance, modifications, troubleshooting, builds, maintenance classifieds. Vents that if plugged will cause fuel to be in order with some from... Needle viton tip off with mineral spirits under 40 deg squiters like Holleys do Suite 600,,. May have been there all along and is worse now for some carburetor tuning assistance level close... Cams will support barely 4 to 6 inches is picking carburetor stumbles off idle out of the carb and all appears be!

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