318 mopar Streetmaster intake. Carb space Blaster 2 coil with new ballast resistor Timing set 12° initial Vacuum is 21” at idle Holley 600 4160 Pink accelerator cam Accelerator adjusted 31 discharge nozzle 65 power valve Screws turned out 1.5 for idle Transfer slots are set at the tiny square Secondary throttle blades set very slightly off the bore Open choke Carb was bought used......the double 2 carbs I had didn’t do this. I needed to remove them for rebuild and maintenance Slight amount of gas was notices on linkage spring connected to throttle shaft Plugs are gapped at 35 Points distributor .017 set with feeler gauge Dwell angle at this setting is 15° Everything else is stock Engine has a flat spot when revving fast. 1100-2000 rpm Engine surges heavily hen slowly raising from idle to higher rpm When driving Engine stumbles and sometimes dies coming off idle Sometimes feathering the throttle keeps it alive Once it gets past about 1600......all the power is there Not sure about this but when I revved it into the higher rpm I don’t thing the vacuum secondaries opened
Start with the basics. Adjust your idle mixture for highest vaccum at your preferred idle rpm. Adjust the accelerator arm..... should be just slightly depressed at idle so there is a shot of gas with throttle movement. There's a technical process for adjusting, but this'll get you in the ballpark. I also wouldn't be afraid of adding a couple more degrees of initial. Keep in mind vacuum secondaries won't open free revving... they need a load. Does your distributor have vacuum advance and if so is it connected to ported vacuum on the primary metering block or manifold vacuum?
Sounds like early (off-idle) has a gremlin acting up. If there's a Holley surgeon here, he'll rec. a set up of accelerator hdwe. I spent more time w/Carter & Rochester, a gradual, smooth fuel delivery would not behave this way.
The idle was adjusted to 21” its the highest I could get. The idle is 700 The accelerator arm is .015....it was adjusted last night. Timing......will go to 15° Vacuum advance is plugged into ported vacuum on the block Confirm....secondary won’t open under free rev. My guess is that it’s opening under load. Problem is definitely in the off idle. Seems like when the main jets take over it straightens itself out. The slow raise in rpm with the surging might be a clue. This is beyond my level.it seems like a lean problem.
This might shed some light hopefully for you https://www.jalopyjournal.com/forum/threads/fixing-the-infamous-off-idle-holley-flat-spot.46534/
If you adjusted the accelerator arm for a .015" gap at idle, that's your problem. It's .015" stroke REMAINING at full throttle.
21" at idle would be a 10.5 power valve for a starting place. Your power valve is normally approximately half of idle vacuum.
Some of it was caused by the secondaries being cracked open too much allowing too much extra air in. I threw a rag on top of the sencondaries and the car died. I took off the carb and closed them up to where you can barely see light coming through them. That solved some of it after retuning it. Adjusting the accelerator pump to have no clearance at idle. It’s just touching and not engaging helped with response. Under no load with the car just sitting there it revs crisp. A slight surge..... Under load..........surge is a lot more pronounced. However......the problem is still there. The thing that stands out here is the steadiness of the problem. It happens about 20° off idle. I can look down the carb and see emulsified fuel coming out of the transfer slots the entire time I’m holding it here.......holding the butterfly’s open with no movement of the throttle. The throttle blades are just above the transfer slots. This is where my problem is Since I’m holding the blades steady, it shows me that maybe the accelerator pump isn’t the problem. Because it’s not working when I hold it steady like this. The blades and pump aren’t moving. I checked the cavuum advance pod. There is a leak in it that would cause something like this. Extra air in through the pod through the ported vacuum port. So I took it off comepletely and plugged the port. The problem stayed. I found a vacuum seal not tight on the air cleaner. Then checked all other vacuum lines to make sure. The problem stayed. It’s a lot better now. The car doesn’t just die when I hit the gas under load while driving. It will pull a hill now. Throttle response is really good but it has to fight through the off idle surge. The screws on he carb are 1 turn out with 21” of vacuum. Turning them out to 1.5 did nothing. The dwell on the distributor is still 15°. I think the distributor cam is worn down. I don’t know if that would cause something like this. The power valve was changed to 8.......it had no effect on the problem. The pump cam is still the pink one for now. The problem is steady enough that I don’t think the problem is here. As said above. I’m getting air in somewhere above idle. It might even be happening at idle and it’s just compensated for because the leak is so small and I have it adjusted to compensate. I did notice that the pcv was hooked up to straight intake vacuum and not the carb base. If I had a small leak......why would my vaccum be so high at idle? That leads me to believe it’s only extra air coming in above idle.
I was thinking power valve too @porknbeaner . 10.5 to start. If that carb has had a backfire in it's lifetime the power valve is toast anyways.
Backfire through the carb, big difference. 1.5 turns on idle mixture screws is just a rough bench setting, so it will be rich enough to start, and idle. It's adjustable because every engine is a little bit different. Otherwise they'd have installed a fixed orifice and saved the 20c in needle valves and springs. Small increments e.g. 1/8 turn make a huge difference in idle A/F ratio. Hardly any air goes through the carburetor at idle, so it depends on engine vacuum in the idle circuit to get things dialed in. The idle mixture screws lean out the fuel as much as possible consistent with a smooth idle. Not saying this will solve your problem but it is consistently adjusted improperly. The transition slot must not be overexposed, and setting this wrong will result in off idle stumble once everything gets buggered. Carb tuning is interesting because every adjustment or baseline setting is very dependent on the one made upstream also being correct... For example, if the fuel pressure or volume from the pump is incorrect, then setting the correct float height will be difficult or impossible. If the float height isn't correct, the fuel height in the bowl won't be right. If the fuel level in the bowl isn't right, then idle mixture settings won't be quite right, jetting will be affected, it may flood, or be starved under wide open throttle etc. When I run into a problem I back up and start with the basics and re-check things "I know" are correct. Assume nothing. Vacuum leaks will bugger good carb operation every time. Ignition/timing is overlooked too. The old saying went that 90% of carburetor trouble is ignition related.
Sounds to me like " lean surge"...when driving the car and the flatspot occurs very rapidly pump the throttle pedal in short pumps, almost like your foot has Parkinson's or is REALY NERVOUS!, this makes the accelerator pump work almost constantly while not allowing a whole lot of air in....if the car likes this it is obviously too lean and needs larger jets. If it has a manual choke running with the choke partially closed also makes it richer and confirms need for more jet.
15 degree's of dwell !? "Points distributor .017 set with feeler gauge Dwell angle at this setting is 15°"
Do you know how long the carb was sitting unused before you installed? I have seen Holley accelerator pump diaphragms get brittle from sitting without gas after being run. You may be getting a partial shot if the diaphragm has hardened. Just a possibility.
Doesn't make sense though. .017 gap should net a higher dwell number. Small gap big dwell. Big gap small dwell. Maybe just a type-o on OP's part. If not and dwell is correct coil isn't able to function correctly.
Feeler gauge on the points.. is really just a bench setting... so it will start.. Then the dwell is adjusted to spec without regard to wherever the point gap might end up at.
Yes, but the relation of the two are way off to make sense is all I'm saying. Another possibility is that OP's dwell meter was set to the incorrect cly selection?
Hey GLHX do you guys have ethanolh blended fuel in your neck of the woods? When we were forced into buying that shit here in New Jersey I had to go larger on the jets on all of my carburetor equipped trucks
You need to confirm your dwell reading. On a V8, it should be 28-32 degrees. The dwell reading is an average of all the cam lobe point openings, a worn distributor cam can give you different timing on each of cylinders. If one (or more) is particularly worn, the timing for that/those cylinder could be off several degrees, which could show up as a surge. The spark is sent to each cylinder when the points open on that distributor cam lobe. Sometimes taking the dwell to either the upper or the lower average reading can reduce the surge. Sometimes adjusting the timing can also reduce the surge. The timing is set based on the timing of the cylinder the light is connected to and it is assumed all the cylinders have the same timing based on the assumption the cam lobes on the distributor are all the same. How old is your Holley? What your getting almost sounds like worn throttle bushings, which could create a vacuum leak at specific throttle positions and would still work well at nearly all other positions. You may be able to over come that vacuum leak by making the accelerator pump give the gas shot a bit quicker then it does now. Gene
The dwell setting. Confirmed it’s 15° set at .017 It is supposed to be 32° The distributor cam block is slightly worn out I think. The most I could get out of it was 28° at .012 The dwell is set to 8 cylinders. It is hooked up to the negative side of the coil and a ground. This dwell reading is correct and yes it’s out of spec. I suspected this to be more of a problem on the upper rpm. Working on an electronic distributor now if I can get it to work. It’s mocked up already but wasn’t working last time. It’s a dual ballast 5 pin mopar box. The throttle shafts leaking. I did pump some air through them with the compressor and some air did come out. The guy at Holley said it was normal because there was no way to completlty seal them. I wondered about this The mixture screws at idle get me 21” of vacuum consistently They are turned out just 1 full turn. Going another 1/2 turn out to 1 1/2 turns made no difference for some reason. The timing right now is set at 12° I’m going to give it more timing to 15° The Holley is 2009 I did go through it all and clear all passages and bleeds. Making the accelerator pump quicker.....that would be a cam right? The pink cam is in there now. If the throttle shafts are the problem. It would fix it on acceleration but what about holding the throttle steady. I haven’t been able to cruise it so I don’t know if the problem happens at Cruise. It does occur while holding the shafts open about 30° and stating there. With this holding the accelerator pump is done. It feels like small surges of extra air coming in about this time. On the higher end it all seems fine. Would bigger jets solve the transfer problem. The transition slots where this occurs are fed by the idle passages and the idle restrictor would stop any fuel fed to them by jetting up??
62 jet Pink cam Bleeds clear Throttle shaft open cover half the cam. Is this normal. Seems fine but I don’t know. This is my first Holley There is a ported vaccum hole right above the transfer slot. It is covered and the transfer slots are square. The secondary transfer slots are closed off as is a vacuum secondary. They are way up in the bore. The problmem only happens when I hold the throttle right above the transfer slots. I’m going to up the power valve to 8.5 But when this problem occurs the power valve isn’t even activated. When the problem is happening the vacuum is 14......when the surge happens the vaccum gauge is unreadable and bounces all over the place. Factor that part in. Look closely at the two pictures with the accelerator pump cam open and closed. It’s offset.
The thing to understand about Holleys is each carb circuit is tuned independent of each other under specific conditions. Idle, transition, power, and cruise. There is definitely overlap but the classic mistake is compensating for a problem in one circuit by over-compensating in another. Jets are always tuned for steady level cruise. It is true that bigger jets will raise the juice flowing at other times, but that's not the way to tune a street motor, it will run pig rich at cruise on the highway. The fact you mention the vacuum gauge isn't holding steady is a tell. It does sound a little like a vacuum leak somewhere. As a test you could try packing the throttle bushings with heavy grease.
Try hooking up the vacuum advance to full time vacuum on the intake manifold.... And plug up the ported vacuum fitting on the carb!!!!
If the power valve was toast it would have more than a flat spot. LOL If you can pull it apart a power valve protector is cheap, last time I bought one it came in a set of 2 for 7 bucks complete with the proper drill bit. If you have a new carb ( like since 1990 newer) it came with a power valve protector from the factory.
I found a vacuum leak in the advance. I plugged it off for now so I’m getting no vacuum assisted advance or I think I did. Might have been the gauge connection. Didn’t have a step down connector. The carb is date stamped 3209 so it does have the power valve protector on it. Packing the throttle bushings with grease is a fantastic idea. I’m going to try that. I have a lot here to play with and I’m getting a really clear understand of all this. On question Why was my vacuum 21” with the secondaries cracked that far. This is basically like a vacuum leak. It shows me that even with an intake leak that vacuum can be that high. How much more vacuum can this engine produce when it’s all sealed up. I’m leaning towards a vacuum leak somewhere so I’ll be focusing on that. The engine has backfired once with this off idle surge. Several other times as well The power valve protector worked well. I checked the valve and it was fine after 6 backfires over time I’ve messed with this. My knowledge on carbureted stuff is limited and far as knowing which symptoms cause what problems. This problem is helping with understanding. The problem is very simple wherever it is
Turkey is on the brain pan, so I may have missed it. On a Holley the float level and needle/seat need to be properly set and in good working order. Is the fuel level, with the engine idling, just below the fuel bowl sights? Both primary and secondary? Verify the needle/seat for the fuel inlet operates freely and smoothly, especially a carb that has been sitting the needle/seat can have a sticky spot limiting fuel flow. Fuel pressure from the pump fine? Not just when idling, but when accelerating as well. Mechanical advance in the distributor working smoothly? Verify the springs and weights are allowed to move freely and do not stick, these always get neglected. The busted vac advance will cause the car to be sluggish to accelerate since you lose that initial lead from the timing at closed throttle, but the mech advance should pickup and work smoothly. It shouldn't be a flat spot, just a tad sluggish/lazy til the weights start to advance the timing.
Just a thought but your ignition is not up to snuff. I would make sure that that is as close to perfect that you can FIRST! Then deal with the rest.You need a few constants first. Gary
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