You said the plugs look black or dark! Sometimes plugs get gas fouled and the won’t hit at wot and will pop! Just had this problem with our race car! Took it to the track with old plugs in it popped cut out at wot and partial, sounded great at idle, real tuff, hitting hard! Owner was pissed, he wanted to do a lot of crap with this and that, I convinced him to put in a new set of plugs, even though they didn’t look that bad, took it out on the street got it into direct, smoked the tires on pavement! Never missed a lick sounded great! Even the other guys in the shop said “ wow”! From a zero to a hero..... with a set of new plugs! Might try it! Edit. We took the engine off the dyno last fall( running great) put it in the car, this winter never drove it anywhere. Set all winter, hauled it to the track last week, ran like shit! Good on dyno.....bad on street??? Sound familiar? Bones
I'm no expert but swade41 seems on the right path. I'm really feeling ignition here. I would really look at spark here. You have already looked at fuel. I've seen the same ghostly issues with my car and a faulty points distributor. Sent from my Pixel 3a XL using The H.A.M.B. mobile app
Wait a minute, you haven’t done anything on the secondary’s and your having trouble at wot? Might want to check the secondary’s! I have zero experience with the Edlebrock, but I think they were patterned off the Q-jet and Carter carbs, and if you didn’t haven’t got things set right on the secondary’s on those, the rear two barrels would hardly work! If I remember correctly! It has been a few years since I worked on one of those! Bones
I am suspect of the wiring or ignition switch. If it ran ok on the dyno Iwould say the problem is in the car. Having 12 volts some place without a load on the system dosen"t mean dam thing. You can have 12 volts on a wire the size of a thread but you can not carry 6 amps and still have 12 volts. Run a jumper wire from the battery to the ignition system.
If you think the accelerator pump adjustment may be an issue: check this url: http://jgronoj.weebly.com/hesitation-or-bog.html I adjusted mine (to the rich mode) and it helped. See below, (graphic from the article). This is an easy adjustment without opening the carb. don
We Really need to get some seat time to solve it. Internet guesses cover that gambit to the extreme. Op said WOT the engine goes silent, no acceleration, then a pop in the exhaust. If we got seat time - Drive along at about 3000 rpm steady cruise and it should be smooth as glass if the ignition is good. If the ignition is weak you’ll usually sense the occasional misfires. If you’re detecting misfires there’s no sense to go WOT. Fix the ignition problem first. I wasn’t there to see what happened so far,,, but The edelbrock tuning process ( based on their theory of operation, mid range transfer circuit and their published procedures) starts with getting the secondary circuit correct first. Then working with the primary. Otherwise one would tend to go richer on primary in attempts to effect the WOT and what happens is the transfer is off and the WOT is off, and the primary is too fat. I’d bet quite a bit this whole thing gets worked out by returning the carb to stock calibration, installing a fresh set of plugs and exquisitely following edelbrock’s tuning procedure and process. It will be the best it can with that equipment.
^^^^^ I messed up once putting metering block assembly back onto a Holley 750 vac. 2nd's. Went did flat at WOT.
Thank you all for the help. As 31Vicky said, this is the plan. I'm getting miles on it first since it runs well when not doing the quick step to WOT. Once the miles are complete per BluePrint, I'll be throwing new plugs in there and following the procedure. The dead spot and pop happen after low RPM light throttle to WOT. Hesitation is much much less when stepping in from 3000 RPM (which is running smoothly at that RPM as well). I'll reply back with results here in a week or so.
Thanks for your write-up on this, I found this a few years ago and found it helpful, Why does an Engine Require Ignition Advance? The gasoline engine is actually a variable compression engine, unlike the diesel. Every time the intake valve opens and air pressure forces in the air fuel mixture, a specific volume of gas (as in "gas, liquid, and solid") is pushed into the cylinder by atmospheric pressure. (We all know that there is no such thing as “suction”.) The amount of gas ingested is dependent on the pressure differential between the atmosphere and the cylinder, and also the displacement of the engine. So, for naturally aspirated engines, the amount of gas that is ingested is normally dependent mainly on the displacement. (Exhaust tuning, or "5 cycle" principle, and also ram tuning are an exception to this. They contribute a supercharging effect to the filling of the cylinder.) Supercharging will vary the amount of gas ingested according to the pressure differential, and can therefore "make" a smaller engine larger, by forcing the smaller engine to ingest what a larger one would normally pump on the intake stroke. Even though the amount of gas that is drawn in is the same, the amount of air/fuel mixture is not. Remember that a solid has a fixed volume and a fixed shape, a liquid has a fixed volume but no fixed shape, and a gas has neither a fixed volume or a fixed shape. This means that a pound of a gas may fill a small peanut butter jar, or a whole room. So, your Y Block cylinder ingests the same amount of gas on each intake stroke, but the amount of air/fuel mixture varies according to the manifold vacuum, which in turn is controlled by the throttle plates in the carburetor. When the throttles are nearly closed, as in cruising at 40 miles an hour, there are only a few oxygen and a few gasoline molecules in the 36.5 cu. inches of air your 292 cylinder ingests. But, when you are going up a hill in second at 30 mph, pulling a heavy load with the throttle wide open, there are many oxygen and many gasoline molecules in the 36.5 cu. inches of air your 292 ingests. So, the effective compression at light load is very low, and the effective compression at full load is high, and highest when your engine is running at the torque peak at full load when the throttle is wide open. That's the point at which your engine is ingesting the maximum amount of air/fuel mixture per intake stroke, and when the compression actually approaches the rated figure of your engine. (This is called "volumetric efficiency", which occurs at the peak torque rpm value.) When your motor is running at light load, there are only a few molecules of fuel and oxygen in the cylinder and they are relatively far apart. So, in order to get them to burn at the right time, you have to start the "fire" (spark) earlier or the piston will be descending before much pressure is generated and power will be wasted. Think of a forest fire. If the forest only has a few trees, it will take a longer time before the forest fire jumps between individual trees and a longer time before the fire reaches the far end of the forest. On the other hand, if the forest is dense with trees, the fire will spread rapidly from one end to the other. This is similar to the case when the cylinder is being completely filled because the throttle is wide open -- each intake stroke contains many, many fuel and oxygen molecules. The spark needs to also occur earlier if the engine is running faster. For a given air/fuel density, there is a specific amount of time that the mixture will take to burn. But, as the engine turns faster, the mixture needs to be ignited earlier so that the burning gasses will make the pressure rise at the right time, giving maximum "push" on the piston. The faster the engine runs, the shorter amount of time the mixture will have to do its work. So, it must be "set off" earlier when the motor is spinning at higher rpm. This is why your engine needs more advance during light load conditions, and less advance when it is pulling under a heavily loaded condition. So, to provide the right spark timing for an engine, two things must be known: the speed of the engine, and the load of the engine. Compression ratio (how closely packed the molecules are in the cylinder) and fuel quality (the ability of the fuel to resist pinging) are factors that distributor tuning must take into account when the distributor is set up.
For less than a hundred dollars you can buy a new HEI dist. assembly and drop it in run a hot wire to it from the battery and see if the trouble goes away. In my experience ruling out a mechanical issue popping through the intake is usually low timing/lean fuel problem and popping out the exhaust is a ignition issue.
I have had a couple eddy carbs that needed float adjustment when new- it’s easy to do and there is a video on you tube by Edelbrock explaining it. The symptoms you are having may suggest that. Don’t worry about ported or full vacuum advance- when you mash the gas your vacuum is gone anyway-the only issue I have had with full vacuum is pinging at tip-in when at steady cruise speed- largely from running my ignition a degree or two more advanced than what the engine likes. 16 degrees seems like a lot of initial- I can never seem to get beyond about 10 or 12 - every engine is a little different though.
Whoa, why does this post sound so familiar! Does the engine rev freely without a load? Run engine then shut it off- climb under hood and check to see if you are getting a good squirt of gas. What kind of fuel pump, electric or mechanical? If electrical, where is it mounted. Did the fuel line have an open end for a while? For electrical, make sure Vac adance is functioning well. Is distributer off a tooth possibly. Are you running PCV valve, could be sucking air at carb. connection.
What is the diode for, and what is is wired between? As far as the 0.9 volts measured across the coil while idling, you have to consider that what you are measuring is the RMS value of the pulsed voltage across the coil. That value depends on the peak voltage, the time voltage is there vs not there (dwell time), etc. In other words, measuring the voltage across the coil at idle with a voltmeter doesn't mean a shit. If you want to know what that voltage actually is, you need an oscilloscope.
I may have missed it or it may not have been mentioned but have you looked at fuel pressure and volume? I have an old AMC that was dropping out under load. Once I swapped in an electric fuel pump with the correct pressure and volume the issues went away. The old fuel systems were designed for old gasoline. The new fuel boils at a lower temperature so the resulting vapors would cause a drop in pressure and volume. I could idle all day long but once I would drive it she went to hell.
Harris, you said the plugs were a little bit black. A couple of us have suggested that you throw a fresh set of plugs in it. I don't think you did that. That surprises me. I would do that before you try to put some miles on it. It's such an easy and inexpensive things to do. If the new set of plugs wakes it up, that would help to really narrow down the possible problems. If not, it still helps. And you've got an extra set of plugs when needed.
Years ago, I rebuilt a 235 Chevy 6. Got it all together, ready to run. Started it up and it ran like shit. Replaced the spark plugs and a couple other things, then I realized it was running rich. Pulled the carburetor and had it rebuilt. Replaced the carburetor and tried it again. Still ran like shit. I started checking everything. Figured the carburetor rebuild might not have been the best. Getting frustrated. My wife came out. "How ya doin, RB?" "Oh, I don't know... everything is new on this damn thing, and it won't run right." "Did you check the spark plugs?" I thought to myself... "Check the spark plugs"... silly girl." I said to her... "Well, no, but they're new, TOO!... because I had replaced them immediately before finding out the carb was bad. But I didn't know what to do next, so after she went inside, I pulled the plugs. A little bit black... not very bad. Replaced them anyway. The engine ran great. I went in and thanked my wife. LOL
Many years ago I did a full but simple tune up on a '70 something Caddy. Sounded OK in shop so I gave it to the customer. It was a comeback. Checked everything over again and again, gave it back to owner and again it came back. Finally out of frustration I pulled the new plugs and replaced them. Ran great, customer happy & I never bought another Champion plug again!
Well after reading thru all the comments I am utterly confused on what he has done or hasn't done.....but in order to properly troubleshoot you need to get your system back to default settings basically. We all know it takes fuel, fire and compression for an engine to run. So if this was my problem I would first verify fire or ignition. Verify and adjust your timing with Vacuum advanced PLUGGED on your distributor. You know the engine runs at idle, but check to make sure your spark is good. Make sure you have a good uninterrupted path of 12 volts to your MSD ignition box. ( Most require their own dedicated 12volts with no other load on the line). Once that is verified and plugs have a solid blue spark and are clean or replaced ( I prefer AC Delco RJ45's) then move on to fuel delivery. Check your fuel float level and make sure it is set correctly, make sure you have the correct power valve in the carb and accelerator pump for your engines specifications. I would not worry about jet sizes unless your running a wild cam and racing it. Also, make sure you have good fuel pressure, most carbs like about 7 to 10 PSI. I would start at 7 psi myself. Make sure your idle air control screws are set correctly. I have always screwed them all the way in and backed them out 1 1/2 turns, then moved them 1/8th of a turn at a time while tuning with a vacuum gauge. Ideally you'll want around 20 in/hg at idle. Make sure your choke is operating correctly and not sticking at WOT. Make sure your throttle plates on your primary and secondary are adjusted correctly. We can start from there and see where this gets you. Also, pics or videos are helpful.
Aren't Edelcrotch carbs fussy on fuel pressure? Too much IIRC is not so good, do you have a fuel pressure gauge on it yet? They are a good diagnostic tool. Do you have another distributor to try in it? I would even try a stock HEI just to rule out your MSD unit. Something plug and play, nothing fancy.
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