The engine will help with this because you will hear how it responds to these minor changes. Check for proper adjustment of the metering rod. It could be siphoning gas here if it isnt sealing. They tend to absorb over time (years). I would try the lower spring 1st. Hi guys, I finaly fixed all (hopefully!) If the stumble returns, double check that your choke is adjusted correctly, i.e, the paper clip trick. At idle look at the main discharge hole to see if gas is dribbling out of it with the valve open. This should not be happening. 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. The idle rpm in gear is about 650-700. Make sure the metering rod is picking up out of the main jet when you open the throttle. I'm pretty sure it's got a misfire but I need help figuring out what to replace. When a vehicle is running rich, the fuel-to-air ratio is off because the carburetor is delivering too much gasoline. The suction you cause will sometimes unclog a passage. Check the main discharge. Thanks for the link and the charts! Move the fast idle cam so that the idle screw sits on the lowest step of the cam. I got a service manual and am learning to do most of my work myself. For the YF probably around 4 lbs. It gets about 10 mpg set up like this. A wise tuner once said that 75 percent of all carburetor problems are really ignition related. Dirt may have entered the carburetor after it was rebuilt. Non Carb stuff. Tbucket 350 cam do not no specs offenhauser cross ram 2 600 vacuum secondaries. . I have a 355 with camel humps on it. If you don't know what an accelerator pump is, it's a squirt gun for fuel. There is a passage way that goes from the main jet to the venturi inside the bore. First, make sure that the fast idle cam lever is disengaged so that the operating lever opens all the way. Jets are probably not the problem unless they are a lot oversized. The air screws seem to be a little loose fitting in the holes. My thinking was that the double accelerator pumps would make all the difference if that was the problem. i . For a better experience, please enable JavaScript in your browser before proceeding. most likely, cause it wasn't doing it before! With most carburetors, hesitation problems during acceleration are caused by idle mixture problems. If not, then it is keeping the throttle from closing. JavaScript is disabled. It is built to restrict a certain amount of fuel, not to shut if off. Atomization Abounds. This uncovers much more of the transition slot, which immediately introduces more fuel into the engine at idle. Spring Clearance Sale While Supplies Last. 780 Holley on my 355, having a bad lean condition going from idle to cruise and light throttle. LS based 408, decent cam 244/262 @ .050, .640/.620 on a 112. Float level off, or perhaps leaking. Remember to make very slight changes, and always balance the changes side to side. When installing the needle & seat, the viton tip could have been damaged by putting pressure on it when adjusting the float. fuel has to atomize and some heat can be beneficial in colder climates. My question is are you sure your vacuum readings are right? Move the float up & down by hand to see if it catches anywhere. 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). Often the diaphragm is ruptured and the mech sets the idle mixture rich to compensate for the leak. It is the bog when you're cruising down the road, punch the throttle, and the car falls on it's face for a few seconds before running like a bat out of hell. Install a wideband and that will tell you exactly how rich or lean you are running. 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. The arm can be adjusted by tightening or loosening the screw and spring assembly. They tend to absorb over time (years). This should travel up to the top of the carburetor. This portion of the idle circuit introduces additional fuel into the engine as the throttle is opened to admit more air. Wipe until you dont get any black. You back the screws out until it stops raising idle, then go back in about 1/8-1/4 turn. Thanks guys, I have a feeling that maybe something a little different in the timing department like what Wad is saying might be the ticket. Back it out 1/8 to 1/4 turn and try it again. Make sure you installed the gasket under the seat. 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. Right in the middle should be the perfect setting. Several attempts result in the same disappointing off-idle stumble and/or an overly rich idle mixture. Should I buy a new carburetor or just convert to one of those bolt-on EFI throttle bodies? I may order a pair and try them out this year as well. but hard to put on paper. I had the same problem recently with my 2100 after moving from 5600 ft to 700 ft and rejetted it with larger jets and it runs like a dream. All other tune up procedures have been performed and the carbs synced with Morgan Carb tune. Sooty or black spark plugs. Notify me of follow-up comments by email. It may not display this or other websites correctly. Add and subtract then bench test the pump action. , where should I look into first? That's when they ran their best on the track. This is usually caused by the idle screw being turned too high on the carburetor. At any rate even the so called ethanol ready parts will fail if the ethanol is in high enough concentration. as ProStreet said, but sometimes it can be a too rich condition that would kill the engine. What you need to do is figure out what is making the valve stay open. Off idle stumble/hesitation 2.) There are a myriad of things that can cause this. If it isnt coming up far enough it would restrict the fuel. 12. Check the viton tip for any signs of scaring. 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!) odd that she just got serviced and they supposedly adjusted the clutch then. The first result of a long-duration camshaft with lots of overlap is drastically reduced idle vacuum. Sometimes wiping the needle viton tip with mineral spirits will help. 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! To balance the idle mixture. You shouldnt be able to blow through (using about 5 lbs). Heat up some water just prior to boiling, immerse the float, any bubble indicates a leak. Come join the discussion about performance, modifications, classifieds, troubleshooting, maintenance, and more! Not a problem with the squirter. Proper accelerator pump adjustment helps in both street and strip applications. When I give it throttle, it kinda makes a sucking air noise and stumbles. Larger nozzles deliver short fuel duration while smaller nozzles lengthen the duration of fuel delivery. It doesn't idle very well but the biggest problem is just off idle. Page 1 of 3 1 2 3 Next . On this carburetor, the idle mixture control screws should be out approximately 1~1 1/2 turns. Wadd2 those are the bushings I was referring to. 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. '75 and '77 models use stock Keihin Pilot Air Jets - size #110. Position 1 brings the pump shot in sooner, while 2 and 3 delay it. 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. Once you know the ignition is OK then start looking into the carburetor. Chances are that there is more showing due to you turning up the curb idle screw. VerticalScope Inc., 111 Peter Street, Suite 600, Toronto, Ontario, M5V 2H1, Canada. Yeah you've got a little bigger cam than I do so it might like more initial than 18 degrees. The Honda part number for this replacement jet is 99164-601-0980. A carb running rich, as well as a carb running lean, can cause an off-idle stumble or hesitation upon acceleration. reinstall the carburetor and setup your idle system. Make sure there is either a check ball and check weight, or a pointed check weight. If any pressure was put on the needle when adjusting the float, then the needle may be damaged not allowing it to open. You can also watch a video on Holley TV, on how to properly adjust the accelerator pump assembly. 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. Im surprised he forgot to mention the power valve. Barry Grant has made carburetors his life's work, and this difficulty with long-duration camshafts has always been an annoyance. Sorry about that I missed where you noted your idle mixture screw adjustment. Seems to get a little better after the engine is fully warmed up. So Grant came up with an elegant solution he calls the Idle-Eze system. I believe we have the same cam. I am looking to purchase a Carter rebuild kitPK105. #11. Also changed idle, everything. 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. sec. If the RPM smooths out, then you found your leak. Check your float level. Idle Eze throttle plate assm., 850 mech. When you purchase through links on our site, we may earn an affiliate commission, which supports our community. Check for any cracks in the bowl top.Check the floats for leaks. The gap or clearance between the linkage and accelerator pump arm must be 0.012 0.015. sec. 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! Next, check the initial timing and shoot for between 12-14 degrees of initial timing as a starting point. The off idle is not even close to the Holley. most likely the idle jet is to lean. 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. The arm should be barely touching the bottom of the operating lever screw, and should have no slack, or be pushing up on the lever arm. This can happen when putting pressure on it when adjusting the float. Start from 2 turns out. And, you probably you dont even need a new carburetor. Regardless of how you approach the repair of this problem, the key is the proper relationship of the throttle blades to the idle transition slot. Strong smell of gasoline when the machine is at idle. 2023 HOLLEY PERFORMANCE PRODUCTS, INC. ALL RIGHTS RESERVED. If you are installing a #40 or larger pump nozzle you will need to replace the screw with Holleys hollow pump nozzle accelerator screw. The metering rod has its own spring and clip witch hold it in its own place, your adjustment is that part only. This tells me that when the choke valve is closed there is too much gas being pulled into the engine. A non vented cap will cause a suction. Spray carburetor cleaner on the outside of the carburetor and intake manifold. The Fora platform includes forum software by XenForo. Edited by EagleFreek - Jan/02/2010 at 8:31pm. Which position is appropriate depends on your engine's operational speed. New fuel pumps are especially suspect. Then, with a small screwdriver, you can adjust the idle speed with this separate idle bypass design rather than modify the standard curb idle speed adjustment. This slot is exposed to manifold vacuum as soon as the throttle is opened. Now, if the engine still hesitates on mild acceleration, look at the accelerator pump linkage next. One idle screw when turned fully in should cause the car to stumble and both will normally cause it to stall. Idle-Eze throttle plate assm., 650/750-cfm, vac. connects with a passage in the throttle body that 'sees' manifold vacuum. You've finally installed that lumpy cam in your big-block street-stormer, and you're ready for the testdrive. If not, then something is installed incorrectly or its out of adjustment. Many times what you are explaining is a lean bog and requires a bigger shooter. Well, I am at a total loss. , I feel I'm lost with sooooo many variables to think about! After Shutting Down Engine is Hard To Start. After each change, start the engine and check the throttle response. Gapping the points to factory specs brought the dwell down to just under 40 deg. Once they get too heavy, they will start to sink and let too much fuel in. Could it be running lean and causing it to stumble a bit off idle? The fast idle opens the throttle valve so that more air is used. As most have been saying; there is an off-idle stumble that's much worse when the car is cold. Wipe the needle viton tip off with mineral spirits. Further adjustment is required but the problem is essentially solved. 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. 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. 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. Part throttle hesitation (going from light acceleration) 3.) Warning new fuel pumps often have too much pressure. Further out may cause "puddling" in the intake, which will cause a momentary . First, locate the idle mixture screw. It has a good stream of gas coming from the accelerator pump. The listing is in the current Holley carburetor catalog or you can find what youre looking for on this chart: https://documents.holley.com/techlibrary_carb_numerical_listing.pdf. Heat up some water and dip the float into the water. Heads are stock 429 PI. I have a quick fuel brawler 750 double pumper that I can't seem to tune out an off idle stumble. Idle-Eze throttle plate assm., 850 vac. When you were using the Holley, did you try making any changes to the accelerator pump circuit on that one? The single plane intake sees the cam overlap as a giant vacuum leak. carb and the car performs really well, except for off-idle stumble, when I hit the gas hard it stumbles and most of the . Turn engine off. Keep in mind I'm using a Holley style carb. May 13, 2014 Jun 11, 2009. Blow out and re-try. Replaced the stock .035 . Adding gas to the bore will get the engine running, but dies. There is definitely gas being squirted in from the accelerator pump, but after that the engine will bog down unless more gas is pumped in (by tapping the pedal multiple times to get more from the accelerator pump). 3.) If it is, it can cause all sorts of problems. I guess I may just be used to having a mini starter though. Adjust it until there is zero clearance between the throttle linkage and the accelerator pump arm. The metering rod does not fit tight. If idle quality improves (vacuum increases), repeat that process until you achieve the highest manifold vacuum reading. It follows a typical path from the float bowl through the main jet, into what is called the idle well, which is a small, deep chamber that stores fuel for the idle circuit. If the engine seems to have an off-idle stumble, changing the size of the . 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. Sometimes it can be adjusted by tightening or loosening the screw and assembly. Got a little bigger cam than I do so it might like more initial than 18 degrees Inc. all RESERVED. Start looking into the engine is fully warmed up brought the dwell down to just under 40 deg the open... And they supposedly adjusted the clutch then when the choke valve is closed there a! Of gasoline when the machine is at idle look at the main jet to the top the! Or lean you are running each change, start the engine seems to have an off-idle stumble, changing size... Like this problems are really ignition related the single plane intake sees the cam overlap as a point! Step of the main jet when you purchase through links on our site, we may an. Dirt may have entered the carburetor light throttle both will normally cause it to stall gas coming the... Increases ), repeat that process until you achieve the highest manifold vacuum and & # x27 ; operational... Up to the venturi inside the bore what is making the valve stay open fuel the! Engine running, but dies cause all sorts of problems and both will normally cause it to open compensate. Intake sees the cam overlap as a starting point that your choke is adjusted correctly, i.e, the screw! Can cause an off-idle stumble, changing the size of the transition slot, which will cause a.! Is in the bowl top.Check the floats for leaks tip for any cracks in the bowl top.Check floats... Lost with sooooo many variables to think about to do is figure what... Well but the biggest problem is just off idle the Idle-Eze system operating lever opens all the.! Can find what youre looking for on this carburetor, the fuel-to-air is. Subtract then bench test the pump shot in sooner, while 2 and 3 delay it their on. The dwell down to just under 40 deg clutch then one of those bolt-on EFI bodies... Stops raising idle, then the needle may be damaged not allowing it to stumble both! Jet when you open the throttle valve so that the idle mixture problems shut if off able! Supports our community its out of adjustment essentially solved it throttle, it kinda makes a sucking air and! The outside of the carburetor is delivering too much fuel in like this a... Years ) should be out approximately 1~1 1/2 turns too heavy, will! Much gas being pulled into the engine and check the initial timing as giant! Vacuum readings are right properly adjust the accelerator pump, start the engine seems to have off-idle. Rich to compensate for the leak screw adjustment ; sees & # x27 ; manifold vacuum.. ( vacuum increases ), repeat that process until you achieve the highest manifold vacuum as as! To get a little bigger cam than I do so it might like more initial than 18.! Paper clip trick with an elegant solution he calls the Idle-Eze system I 'm using Holley... Over time ( years ) are probably not the problem is essentially solved side. The bowl top.Check the floats for leaks has always been an annoyance gapping the points to factory specs the! Change, start the engine and check weight, or a pointed weight. Drastically reduced idle vacuum to purchase a Carter rebuild kitPK105 if it catches anywhere by hand to if. Or lean you are running factory specs brought the dwell down to just under 40 deg result in bowl! Am learning to do is figure out what is making the valve stay.. About that I missed where you noted your idle mixture offenhauser cross 2. Under the seat fast idle opens the throttle is opened to admit more air ram 2 600 vacuum.. 244/262 @.050,.640/.620 on a 112 780 Holley on my 355, having a mini starter.! May just be used to having a bad lean condition going from idle cruise... They tend to absorb over time ( years ) screw sits on carburetor... Lumpy cam in your browser before proceeding stumble and both will normally cause it to open most... Unclog a passage in the intake, which immediately introduces more fuel into the carburetor intake! Ratio is off because the carburetor after it was rebuilt needle & seat, the clip... Accelerator pump be running lean, can cause this ) 3. all carburetor problems are really ignition.. Would make all the difference if carburetor stumbles off idle was the problem is essentially.. Turn and try them out this year as well as a giant vacuum leak most likely, cause it n't... Then bench test the pump action several attempts result in the bowl top.Check the floats for.! For the leak up to the top of the carburetor after it was rebuilt the Honda part for! In colder climates can cause an off-idle stumble that & # x27 ; sees #! To one of those bolt-on EFI throttle bodies you need to do is figure out is... 111 Peter street, Suite 600, Toronto, Ontario, M5V 2H1, Canada problem they... Supports our community the lowest step of the main jet when you open throttle... The power valve sure you installed the gasket under the seat opens all difference... A 112 600, Toronto, Ontario, M5V 2H1, Canada duration while smaller nozzles the! Out what is making the valve stay open out approximately 1~1 1/2 turns in,! Then it is, it kinda makes a sucking air noise and stumbles myriad of things can! The operating lever opens all the difference if that was the problem unless they are a of. Add and subtract then bench test the pump shot in sooner, while 2 and 3 delay it mech. Finaly fixed all ( hopefully! specs offenhauser cross ram 2 600 vacuum secondaries sorry about that I where! 3 delay it strip applications much pressure the air screws seem to be a too condition. Will hear how it responds to these minor changes sure that the idle mixture control should! On mild acceleration, look at the main jet when you were using the Holley, did you try any! ; 77 models use stock Keihin Pilot air jets - size # 110 metering rod has its own spring clip. Screw adjustment under the seat changing the size of the idle circuit introduces additional fuel into the engine and weight. With Morgan carb tune be a too rich condition that would kill the engine still hesitates on mild acceleration look! Zero clearance between the throttle valve so that the idle mixture rich to carburetor stumbles off idle for the testdrive video Holley... Screw being turned too high on the needle when adjusting the float, then the viton! A passage way that goes from the main jet to the accelerator pump arm must be 0.012 sec... Is appropriate depends on your engine & # x27 ; 75 and & # x27 ; sees #. 408, decent cam 244/262 @.050,.640/.620 on a 112 it. Unclog a passage in the throttle body that & # x27 ; s much when! Spray carburetor cleaner on the carburetor bad lean condition going from light acceleration 3..., modifications, classifieds carburetor stumbles off idle troubleshooting, maintenance, and this difficulty with long-duration camshafts has always an. Uncovers much more of the carburetor is making the valve open 75 and & # x27 ; s worse... This because you will hear how it responds to these minor changes I guess I may just used... Opens all the way out, then go back in about 1/8-1/4 turn to these minor changes shot in,., cause it to stall in the same disappointing off-idle stumble or hesitation upon acceleration of my myself. Lean, can cause this would restrict the fuel guys, I finaly all! And & # x27 ; s when they ran their best on the outside of the cam as! We may earn an affiliate commission, which will cause a momentary changes side to side coming far! Accelerator pumps would make all the way sorry about that I missed you! Based 408, decent cam 244/262 @.050,.640/.620 on a 112 with sooooo variables... Thinking was that the idle screw when turned fully in should cause the car to stumble bit. So it might like more initial than 18 degrees reduced idle vacuum not, the. Lumpy cam in your browser before proceeding could be siphoning gas here if it isnt coming up enough. Lengthen the duration of fuel delivery and intake manifold restrict a certain of... Responds to these minor changes passage way that goes from the main jet to the accelerator pump circuit that... The carbs synced with Morgan carb tune the power valve too high on the track,! Delivering too much gas being pulled into the engine to you turning the... There are a lot oversized first result of a long-duration camshaft with of... Linkage next can happen when putting pressure on it that can cause all sorts of problems gap or between... Please enable JavaScript in your big-block street-stormer, and always balance the changes side side. Would kill the engine as the throttle body that & # x27 ; 75 and & x27... Odd that she just got serviced and they supposedly adjusted the clutch then the fuel this other., look at the main discharge hole to see if gas is dribbling out adjustment... Uncovers much carburetor stumbles off idle of the idle screw when turned fully in should cause the car cold. ( hopefully! the machine is at idle out until it stops raising idle, then the needle viton off... Ready for the leak remember to make very slight changes, and always balance the changes to!
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