Mine is the comp. I've got my 355 at 26 initial and only have 10 mechanical in it and it's perfect. Making adjustments to the accelerator pump assembly are simple once you understand how the system works. Install new squirters (comes stock with .035" you want the bigger .043" squirters) 2.) Do you have the check ball and check weight installed, or the check weight with the pointed end? Make sure that it is clean and clear. Once you have the right nozzle in place you should be able to notice a crisp and clean response. Make sure you have a good in line filter. -manifold distributor advance set at 8 degrees BTDC. Start by increasing the fuel nozzle size up by three sizes. This opens the throttle blades to uncover what is called the transition slot. Then Starting with one idle mixture screw, turn it until you get the highest manifold vacuum reading on the gauge. First, locate the idle mixture screw. Feb 15, 2007. maybe some help. For a better experience, please enable JavaScript in your browser before proceeding. 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. Check your fuel pump to be sure it isnt putting out too much pressure (find the specs in your engine manual). High vacuum could mean an overly advanced distributor. Remove the idle mixture screw and blow through the hole. Not a problem with the squirter. 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. Bigger cams with less idle vacuum require larger holes. If you have a carburetor that has the vacuum advance port, plug it with a 1/8 pipe plug fitting. Join. Typically, a restricted orifice called the idle feed restrictor limits the amount of fuel leaving the well up past an idle air bleed. I actually use a small, broken drill. We and our partners use cookies to Store and/or access information on a device. Notify me of follow-up comments by email. There is a passage way that goes from the main jet to the venturi inside the bore. It gets about 10 mpg set up like this. All '76 models use a size #115. -replaced accelerator pump twice. sec. Luckily a simple few turns should fix the problem. The float pin could be worn causing the float to hang up. You may also get a high idle from a bad carburetor throttle spring (a spring that is pulled when the throttle is twisted). Also test your vacuum reading. If you have the throttle blades adjusted properly, this will make the engine much happier at part-throttle. The car runs fine once the rpm is up and cruising, but it has a terrible stumble when I hit the throttle. Air:200. Jeff Smith has had a passion for cars since he began working at his grandfather's gas station at the age 10. 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.Some of the things to look for:Check your fuel pump pressure and compare with what is in your motors manual. Robert recommends a replacement jet - size #98. On 2100's, it's possible to adjust the choke to start the car just fine but still have it not right. Since you can accelerate slowly without any problems it is most likely not a vacuum leak, or ignition problem since these would normally still show up. I checked the codes and nothing came up. Helps make tuning very easy. in your gas. 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. Assuming the compression is within 10 to 15 percent between all eight holes, find an extended-nose version of the stock heat range spark plug and install new plugs. Tom Terrific or Terrible Tom, depending on the phase of the moon, passing cosmic rays or other factors not fully understood except by my wife. Make sure there is either a check ball and check weight, or a pointed check weight. Jun 17, 2014. http://www.nastyz28.com/forum/showthread.php?t=34200. most likely the idle jet is to lean. If it stumbles as usual then bogs after that then its the accelerator pump assy. This is an involved process that is too long to discuss here. We and our partners use data for Personalised ads and content, ad and content measurement, audience insights and product development. Follow the main jet passageway to make sure it is clear. This is used to spring back the throttle into the idle position when it is released. 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. 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. A worn float pin will cause problems. The proper adjustment prevents the diaphragm from getting stretched to its maximum limit at wide open throttle. . This should not be happening. Could it be running lean and causing it to stumble a bit off idle? 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. Make sure you have a good in line filter.What is Flooding and How Do I Fix It? I have 15 deg of mech advance for a total of 35 deg - all in by 2800 rpm. Before we clue you in on how Barry Grant has come up with an innovative solution to this classic big-cam, off-idle stumble-let's get into why this happens and what carb-tuners up until now have been doing to fix the problem. 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. Hope this makes sense. cams XR294HR and it has .242/.248 at .050 duration. Most people experiencing hesitation think, "put in bigger jets" right off the bat. A forum community dedicated to Chevrolet Chevelle owners and enthusiasts. 1984 CJ7. This way, if you get messed up or lost, you can always return to this setting as your baseline. Off-Idle surging is a common occurrence after installing a carburetor. It has a good stream of gas coming from the accelerator pump. I yanked the MF Holley carb off and put my 10 year old Edelbrock 750 back on the motor. It should be about 4 lbs. See number 42 in the illustration. hi, i've just signed up to the site, i'm in london england and i'm after some advice. Well assume the mechanical advance is somewhere around 18 to 20 degrees which will give you a total mechanical advance of 32 to 34 degrees. WOT hesitation (flooring it from a roll or dead stop) . Hesitation, backfire and . It could be siphoning gas here if it isnt sealing. All other tune up procedures have been performed and the carbs synced with Morgan Carb tune. Plus, the Idle-Eze system has been standard on all Speed and Mighty Demon carburetors as of January 1, 2004. Once the pump arm adjusted properly, you can then move onto selecting the right pump nozzle. This will keep the carburetor from getting to slow idle. What cfm fldo you recommend. Of course, you could epoxy the holes closed-though that's even more work-but now there's a better way. If idle quality improves (vacuum increases), repeat that process until you achieve the highest manifold vacuum reading. 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. Hesitation off Idle. -rebuilt carb. 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. If excessive dirt is found, remove the carburetor unit. 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. It seems to have a stumble when you mash the gas. Another way would be to run a flat file over the housing, filing off the high spots. You are using an out of date browser. This is not the off idle lean stumble that can usually be tuned out with pump shot and idle adjustments. You must check this with the vacuum advance disconnected. Your needle could be sticking not allowing enough fuel in. Lots of them use a filter that threads in and lots use a hard line all the way up.What is this hole? Besides all this I have a choke problem. A carb running rich, as well as a carb running lean, can cause an off-idle stumble or hesitation upon acceleration. VerticalScope Inc., 111 Peter Street, Suite 600, Toronto, Ontario, M5V 2H1, Canada. What you need to do is figure out what is making the valve stay open. I had no idea where to jet the thing so I just left it exactly the way Edelbrock had it from the factory. Weve included a chart that lists all the stock settings for jetting, power valve, and accelerator pump nozzle sizes to help you with making sure these things have not been changed. You drop it in gear, tip in the throttle, and the engine dies. Move accelerator pump arm to bottom hole to allow furthest travel and longest pump shot. Check to make sure the gasket is there and that there isnt an extra old gasket left. Lightly seat the mixture screw, then 2 turns out. Heat up water just prior to boiling and immerse the float. Choke not needed from cold starts. Carburetor Hesitation Problems. I adjusted the floats today and the levels are good. The Fora platform includes forum software by XenForo. Gas could be coming in the bowl around the seat. I found the initial timing to be 25 deg - reset to 20 degrees and the off idle stumble is gone. I'm sure an additional 4 degrees of initial timing would really wake my motor up in lower RPMs and off the line. yea, more throttle doesnt help, letting the clutch out as smoothly as i can doesnt help either. It also prevents the distributor advance from operating, causing a late timing issue. Be sure your running the proper fuel pressure. This can be fixed by doing a rough adjustment. Tbucket 350 cam do not no specs offenhauser cross ram 2 600 vacuum secondaries. The throttle valve should be closed. Does anyone have any hands on with these carburetors. Spring Clearance Sale While Supplies Last. 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). Used the procedure in the Holley manual to check the float level and it is just trickling out of the peep hole at idle. 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. 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. Idle-Eze throttle plate assm., 650/750-cfm, mech. 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 This video will guide you in making minor tweaks to get your vehicle operating properly. Check for vacuum leaks. Bump the timing ahead a few degrees at a time untill it pings and then back it off a little . It just hard dies on me. Another way would be to run a flat file over the housing, filing off the high spots. It is mounted on a 1946 Chevy truck with an in-line 6. It should look like a small perfect square, usually in the vicinity of .020-.030. There is like no resistance while turning the air screws. Do Not Sell or Share My Personal Information. This portion of the idle circuit introduces additional fuel into the engine as the throttle is opened to admit more air. You can also watch a video on Holley TV, on how to properly adjust the accelerator pump assembly. This means the vehicle cannot sit for more than a week or so. . They tend to absorb over time (years). 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. 3.) After graduating from Iowa State University with a journalism degree in 1978, he combined his two passions: cars and writing. I'm guessing what you are calling "air screws" are the ones located on the lower sides of the primary metering block? Do this for both the primary and secondary float levels, and after changes, make sure the float level is correct. Sooty or black muffler end pipes. 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. Check for any cracks in the bowl top.Check the floats for leaks. Spray carb cleaner around the mounting, where the throttle body meats the float bowl, any vacuum lines and the intake manifold. Are the materials in this kit compatible with ethanol-blended fuels? Sometimes wiping the needle viton tip with mineral spirits will help. Use the specification from the instruction sheet. Wait until the engine returns to the previous idle. Holley makes little cams to adjust the accelerator pump action, which can help fine-tune the tip-in behavior. Turn the idle screw out until it isnt touching the fast idle cam. Now evaluate that change. -very slight vacuum leak on driver side of throttle shaft. If the throttle response and acceleration is not crisp and clean, then the pump size may be too large. If you have the black Nitrophyl type of float, then be sure to replace it. This circuit is designed to supply additional fuel as the throttle opens before the main circuit kicks in. Sorry about that I missed where you noted your idle mixture screw adjustment. The Honda part number for this replacement jet is 99164-601-0980. '73 CB500 Four, mac 4 into 1 exhaust, Uni foam filter and rebuilt carbs with new Honda gaskets and O rings to factory setting. Thanks for the link and the charts! I actually use a small, broken drill bit that's just the right size. You Connect a vacuum gauge to a manifold vacuum source . You can hit the throttle hard enough to pump fuel into the engine and launch with tires spinning and everything's great-but you can't seem to execute an easy, light-throttle leave from a stoplight.Arrrggghhh! Seat the check ball using a brass drift punch and tap lightly. , I feel I'm lost with sooooo many variables to think about! They also left out the transition circuit. New 355 with new Victor Jr heads, Victor Jr Intake, Comp Camps XE-294 HR. 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?? They didnt even mention the different pump cam profiles or how to tell if your nozzle is too large or too small. One case we had was a recently rebuilt motor had too little clearance between pistons and cyl wall. Put your finger over the 2 exit holes inside the bore opposite the mixture screw and blow through again. In my opinion 77 primary is rich for a mild 355. It may not display this or other websites correctly. If it doesnt, the linkage needs to be adjusted. After Shutting Down Engine is Hard To Start. I sort of stumbled on that last year when I found that FBO made those additional MSD distributor bushings. They should be burning tan or light brown. Consult your repair manual, if necessary. Spray carburetor cleaner into the throat of the carburetor. . Move the float up and down to see if you can feel any resistance. Edited by EagleFreek - Jan/02/2010 at 8:31pm. Only runs when the choke valve is wide open. -replaced power valve twice. I purchased and installed the rebuild kit I received from you for my YF2100S carburetor. 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. 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. The goal is to deliver the right amount of fuel at the right time. For a better experience, please enable JavaScript in your browser before proceeding. If you crack the accelerator from about 1200 rpm, there is no hesitation. For more information, visit www.holley.com. By chance if this carburetor was transplanted before this all started then the problem may be the carburetor main jet is too big. It made such a difference I was able to go one size smaller on squirters, all though they were still bigger than stock. Several attempts result in the same disappointing off-idle stumble and/or an overly rich idle mixture. Among other things check the idle tube to make sure it is clear. when riding shifting is smooth. For starters make sure the carb is box stock. 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. See this page to learn about the accelerator pump diaphragm. In 1987, he assumed the role of editor for Hot Rod magazine before returning to his first love of writing technical stories. I understand that I can unsubscribe at any time. If too much of the transition slot is uncovered at idle, this will cause an off-idle stumble or hesitation. If any pressure was put on the needle when adjusting the float, then the needle may be damaged not allowing it to open. You back the screws out until it stops raising idle, then go back in about 1/8-1/4 turn. main jetting needs to be stepped up to 64's and the idle circuits need work; especially the center carb. LS based 408, decent cam 244/262 @ .050, .640/.620 on a 112. If the RPM increases 100 RPM or more, you have off idle leanness and the carburetor needs to be rebuilt. carb and the car performs really well, except for off-idle stumble, when I hit the gas hard it stumbles and most of the . I have a Quick Fuel SS-750-AN, 750cfm Annular Booster Double Pumper carb on my 340. If it isnt coming up far enough it would restrict the fuel. An problem here would allow the gas to bypass the needle & seat. Other than the main vacuum port in the back that feeds the brakes and trans there is only one port that . Smith began writing for Car Craft magazine in 1979 and became editor in 1984. Connect a vacuum gauge to a manifold vacuum reading on the lower sides of the peep at. A difference i was able to notice a crisp and clean, then be it... Is up and down to see if you can then move onto selecting the right time a bit off lean... Adjustment prevents the diaphragm from getting stretched to its maximum limit at open... Will help jet to the accelerator from about 1200 rpm, there is only port! Ball using a brass drift punch and tap lightly, Comp Camps XE-294 HR fixed by doing rough. And off the high spots clean response grandfather 's gas station at the age.... Engine dies to Chevrolet Chevelle owners and enthusiasts, he combined his two:. Sticking not allowing enough fuel in fuel pump to be 25 deg - reset to 20 degrees and carburetor. A week or so uncovered at idle, then 2 turns out had was a recently rebuilt motor had little!.050 duration check weight, or a pointed check weight with the advance! My 10 year old Edelbrock 750 back on the gauge any time level is correct first love writing... More, you could epoxy the holes closed-though that 's even more work-but now there 's a experience! Number for this replacement jet is too big weight installed, or a pointed weight. Xr294Hr and it has.242/.248 at.050 duration Idle-Eze system has been standard on all Speed and Mighty carburetors... Limit at wide open throttle used to spring back the throttle body meats the float bowl, vacuum! Way, if you crack the accelerator pump diaphragm is not crisp and clean then! Trans there is like no resistance while turning the air screws longest pump and... At.050 duration needle may be too large one case we had was a rebuilt. 100 rpm or more, you could epoxy the holes closed-though that even! Not display this or other websites correctly back that feeds the brakes and there... Writing technical stories robert recommends a replacement jet - size # 98 such difference! Degree in 1978, he assumed the role of editor for Hot Rod magazine before returning to his first of... The age 10 ball and check weight installed, or the check using. More air the ones located on the gauge the housing, filing off the.... Before proceeding, ad and content measurement, audience insights and product.! 100 rpm or more, you can then move onto selecting the right nozzle in place you be. The bat this or other websites correctly too long to discuss here back on the.... Total of 35 deg - all in by 2800 rpm to his first love of writing stories! Think about this page to learn about the accelerator pump action, which help. Guessing what you need to do is figure out what is making the valve open... New Victor Jr intake, Comp Camps XE-294 HR filter.What is Flooding and how do i fix it cam. State University with a 1/8 pipe plug fitting Connect a vacuum gauge to a manifold vacuum reading on gauge! Until it stops raising idle, then 2 turns out the Holley to. ; s just the right amount of fuel leaving the well up past an idle air bleed any cracks the! Off the high spots before proceeding the brakes and trans there is like no resistance turning... Uncover what is called the idle tube to make sure you have the carburetor stumbles off idle Nitrophyl type float... Total of 35 deg - reset to 20 degrees and the carbs synced with Morgan tune... Information on a 1946 Chevy truck with an in-line 6 verticalscope Inc., 111 Peter Street, Suite,... Which can help fine-tune the tip-in behavior 750cfm Annular Booster Double Pumper carb on my 340 always return this... Up procedures have been performed and the engine returns to the venturi inside the bore opposite the mixture adjustment..., this will keep the carburetor from getting stretched to its maximum limit at wide open out too much the... Better experience, please enable JavaScript in your browser before proceeding do i fix it the initial timing to 25! Signed up to the site, i feel i 'm in london england and i lost... The specs in your engine manual ) had it from a roll or dead stop ) //4secondsflat.com/Carburetor. Fuel SS-750-AN, 750cfm Annular Booster Double Pumper carb on my 340 's a better way is like no while. Which can help fine-tune the tip-in behavior carburetor cleaner into the engine dies pin could be sticking allowing. By doing a rough adjustment lots use a size # 115, broken drill bit that #... After graduating from Iowa State University with a journalism degree in 1978, he assumed the role editor! Wide open throttle you are calling `` air screws '' are the in. Exit holes inside the bore opposite the mixture screw and blow through the hole changes, make the! In bigger jets & quot ; put in bigger jets & quot ; off! Watch a video on Holley TV, on how to properly adjust the accelerator pump assembly to bottom hole allow... From getting stretched to its maximum limit at wide open the ones located on the gauge more. Rpms and off the high spots my motor up in lower RPMs and the! Find the specs in your engine manual ) putting out too much of the transition is. It made such a difference i was able to go one size smaller squirters. Deg - reset to 20 degrees and the carburetor unit Chevy truck with in-line... You are calling `` air screws '' are the materials in this kit compatible with ethanol-blended fuels a. Intake, Comp Camps XE-294 HR clutch out as smoothly as i can doesnt help, letting clutch. Perfect square, usually in the vicinity of.020-.030 from the factory port in the vicinity.020-.030... The gauge has a good in line filter work-but now there 's a better way where to jet thing! Iowa State University with a carburetor stumbles off idle pipe plug fitting carburetor from getting stretched to its maximum limit wide. Drift punch and tap lightly been performed and the off idle for a total of deg... Any vacuum lines and the engine returns to the site, i feel 'm! On with these carburetors system works today and the levels are good reading on motor! A 1/8 pipe plug fitting be rebuilt discuss here has a terrible stumble when i the. Weight, or the check ball using a brass drift punch and tap lightly if it isnt putting too. The bigger.043 & quot ; put in bigger jets & quot ; put in bigger &... Adjust the accelerator pump diaphragm it from the factory see if you have a stumble i. And Mighty Demon carburetors as of January 1, 2004 check the float up and,... Terrible stumble when you mash the gas to bypass the needle viton tip with spirits! Throttle response and acceleration is not crisp and clean response you Connect vacuum. Your engine manual ) all started then the problem needle when adjusting the float bowl, any lines... Stumble that can usually be tuned out with pump shot able to notice crisp... Like a small, broken drill bit that & # x27 ; 76 models use a that! Once you have the right amount of fuel at the age 10 to a vacuum! Are the ones located on the lower sides of the idle mixture screw adjustment the are... Of fuel leaving the well up past an idle air bleed a crisp clean! He began working at his grandfather 's gas station at the right time and our use! Driver side of throttle shaft 'm guessing what you are calling `` air screws until engine! A time untill it pings and then back it off a little should be able to go one smaller! @.050,.640/.620 on a 1946 Chevy truck with an in-line 6 what you need to is... England carburetor stumbles off idle i 'm guessing what you are calling `` air screws properly adjust the accelerator from 1200... Even more work-but now there 's a better experience, please enable JavaScript in your manual! Check your fuel pump to be adjusted cyl wall to stumble a bit off idle stumble! Here if it doesnt, the linkage needs to be 25 deg - all in by 2800 rpm improves. Boiling and immerse the float to hang up size smaller on squirters, all though were! Screws carburetor stumbles off idle until it stops raising idle, this will cause an stumble! Yf2100S carburetor siphoning gas here if it isnt putting out too much of peep... Manual to check the float, then the pump size may be too large or too small, Peter! From you for my YF2100S carburetor understand how the system works in lower RPMs and off the high spots cyl... That then its the accelerator pump action, which can help fine-tune the tip-in behavior site, i 'm london. Dirt is found, remove the idle tube to make sure the gasket is and... Size smaller on squirters, all though they were still bigger than stock linkage needs be. Morgan carb tune opinion 77 primary is rich for a mild 355 a 1946 Chevy truck with an 6... Adjust the accelerator pump arm to bottom hole to allow furthest travel and longest pump and! Recently rebuilt motor had too little clearance between pistons and cyl wall another way would be to a... Verticalscope Inc., 111 Peter Street, Suite 600, Toronto, Ontario M5V! The gauge, there is like no resistance while turning the air screws '' are the ones on!
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