Engine Bogs and Misses Under Hard or Mild Acceleration

[CRW-FK5]

I have been having what appears to be a worsening condition in my 440 where under even mild acceleration the car stumbles and hesitates significantly.  If I push hard on the pedal, forget it.  It will kick back hard.  In addition to this, I cannot seem to get rid of a persistent ping.  I suspected perhaps a bad batch of gas, but it has been going on too long for that.  Backing off the timing does not effect the bog or get the pinging to go away either, even when at 8° BTC.  I have checked timing marks on balancer by setting up piston block in #1 and marking when piston stops in both clockwise and counterclockwise directions and confirmed that the distance between marks on balancer equal the factory mark.  I have replaced the aftermarket Edelbrock with another one with no difference.  I have pulled the distributor and checked for things like broken mechanical springs.  I have disconnected vacuum advance.  I have added 2 gallons off 110 fuel to full tank (this seemed to help reduce pinging but not eliminate it).

My engine did not behave this way a year ago, and seems to be getting worse.  I am running electronic ignition with chrome ECU.  Any ideas on what could be causing this would be greatly appreciated.

[c00nhunterjoe]

Lack of fuel pressure or a jumped timing chain.

[68 RT]

Lean, I would agree with above you are losing fuel pressure, fuel pump rod or bad pump.

[CRW-FK5]

Lean, I would agree with above you are losing fuel pressure, fuel pump rod or bad pump.

With a bad pump I would not expect an immediate reaction when I hit the pedal, since during initial acceleration the system should be pulling from full bowls.  If the hesitation occurred a few seconds later (due too bowl level reduction) I could see it being fuel delivery related.  I am leaning towards timing chain.  Is it possible to be able to adjust ignition timing back in with a jumped tooth, ending up with just valve timing off?  And with that, would I end up with the described performance issue?

[c00nhunterjoe]

Is the engine stock? Got alot of age on it?  It could still be a lean shot problem. Could be a wiped cam. Could be alot of things. I would start with fuel pressure 1st before pulling the timing cover. A compression test is another easy test and be my 2nd check.
   And no, adjusting ignition timing will not fix valve timing if it is a stretched chain. While not impossible, it is improbable. I have seen far more small block chevies jump time then big block mopars.

[BSB67]

  I have replaced the aftermarket Edelbrock with another one with no difference. 

Could you please expand on this

[CRW-FK5]

Is the engine stock? Got alot of age on it?  It could still be a lean shot problem. Could be a wiped cam. Could be alot of things. I would start with fuel pressure 1st before pulling the timing cover. A compression test is another easy test and be my 2nd check.
  And no, adjusting ignition timing will not fix valve timing if it is a stretched chain. While not impossible, it is improbable. I have seen far more small block chevies jump time then big block mopars.

Thanks.  I bought the car a little over a year ago so I'm not sure how tired it is.  I did, however, do a compression test on it last weekend and all cylinders are between 170 & 185 psi (cold engine).  The engine has decent street cam (Purple Shaft) and I believe at least 10:1 compression ratio.

Regarding the ignition timing, I did not mean to imply that I could correct valve timing by adjusting ignition timing, as I am aware that valve timing is determined by cam & crank sprocket position.  I wondered if perhaps I had jumped a tooth would I even be able to readjust ignition timing back to correct position.  If a jumped tooth would not allow ignition timing to be corrected then I could confirm that I did not jump a tooth.  Just a possible way to diagnose the problem without digging into it first, that's all.  Thanks for your  feedback.

[CRW-FK5]

  I have replaced the aftermarket Edelbrock with another one with no difference. 

Could you please expand on this

Sure.  I have a 750 Edelbrock on there now.  A friend had a 650 (or 600, not sure) Edelbrock that I put on just to see if the problem was carb related.  I got the same bogging with the other carb.

[68 RT]

You need to richen up the edelbrock, I had to do mine. Same problem you are having. Most edlebrocks are lean from the factory. Buy the strip kit it has everything you need. Mine had to go up 2 jet sizes on the primary and I think down on the metering rods. Also changed the metering rod springs. Very easy to do. Start with the springs. Also have you pulled any plugs to check for lean? 

[BLK 68 R/T]

Bad or loose magnetic pickup in the distributor?

[69_XS29L]

I had a similar problem many years ago on my 440.  Original stock ignition coil was faulty, start and run fine, but stumble bad or die under even light to moderate load. I'd check everything in the secondary ignition or high voltage side for voltage leaks, carbon tracking, opens or potential shorts before I threw any amount of money at the problem. Old school oscilloscope would be a good help.
Good luck, Mike

[CRW-FK5]

You need to richen up the edelbrock, I had to do mine. Same problem you are having. Most edlebrocks are lean from the factory. Buy the strip kit it has everything you need. Mine had to go up 2 jet sizes on the primary and I think down on the metering rods. Also changed the metering rod springs. Very easy to do. Start with the springs. Also have you pulled any plugs to check for lean? 

I do have the kit (#1489) and did try opening up the jets last year.  I also recall changing rods to richen up a bit.  No improvement but may not have been changing the right parts.  I didn't mess with the spring, however, so that's something I could try.  Which way would you go with them?  Towards lower in. Hg?  I've attached a picture of the springs below.  I think I have the colors correct but if you could confirm, that would be great.  From left to right, Blue (3"), Yellow (4"), Orange (5"), Pink (7"), Silver (8").

Regarding the plugs, they don't look lean to me.  Actually look okay.  See pictures below.

Thanks for your help.

[CRW-FK5]

Here is a picture of rotor position at TDC on #1.  I don't know how far off it would be if I had jumped a gear tooth but if it's significant I would think someone might be able to tell me if I'm off, relative to angle in picture.  To me it looks pretty close to where it should be, but would love to get confirmation.

[birdsandbees]

..sorry, that was with timing gear marks lined up.

(I had showed a picture that the rotor tip should point at the #1 cylinder with the timing gear dots lined up)

[CRW-FK5]

Yes.

[XH29N0G]

I think when the others are taking about jumping a gear, they are describing the timing chain and the timing on the cam (affecting valve timing).  This, as you said is different from the spark timing.  

Where the rotor points depends in part on how the distributor is installed so I do not think that will tell you whether the timing chain jumped.  

If the timing chain jumped, the only thing I can think of is either taking a look at the sprockets with the timing chain cover off to see if the timing marks line up or (better) determining where the lobe center is with a dial indicator.  I am not an expert in this and some who have answered already can provide clear information on whether what I have written is valid.  Both of these tests are possible, but fairly involved to do.


That said.  Your cold compression test does not strike me as crazy high though. 

[CRW-FK5]

I checked the play between crank gear and distributor and found it to be right around 7.5°.  Is this too much?

Picture below shows point (from 0° mark) where distributor rotor begins to rotate.

[CRW-FK5]

I think when the others are taking about jumping a gear, they are describing the timing chain and the timing on the cam (affecting valve timing).  This, as you said is different from the spark timing.  

Where the rotor points depends in part on how the distributor is installed so I do not think that will tell you whether the timing chain jumped.  

If the timing chain jumped, the only thing I can think of is either taking a look at the sprockets with the timing chain cover off to see if the timing marks line up or (better) determining where the lobe center is with a dial indicator.  I am not an expert in this and some who have answered already can provide clear information on whether what I have written is valid.  Both of these tests are possible, but fairly involved to do.


That said.  Your cold compression test does not strike me as crazy high though.  

Thanks.  Yes, but since the distributor is driven from the cam, both ignition and valve timing would shift if the chain jumps.  Ignition timing can be brought back in through adjustment to some extent, but obviously valve timing cannot.  I could have inadvertently brought ignition timing back in a while back not realizing I may have had a chain issue.  That was my thinking.

Relative to the distributor installation, the distributor can only be installed in 2 different positions, 180° apart, due to the slot in the bottom that drops into the gear.  So there is really no way I could have put the distributor in wrong without noticing it.

[XH29N0G]

I see your point.  (I mentioned the valve timing because I had a car where a timing belt slipped and it really behaved poorly - not detonation though). 

I do not know about the 7.5 degree play in the distributor, that doesn't seem right to me.  I hope you get this solved quickly.

[68 RT]

You need to richen up the edelbrock, I had to do mine. Same problem you are having. Most edlebrocks are lean from the factory. Buy the strip kit it has everything you need. Mine had to go up 2 jet sizes on the primary and I think down on the metering rods. Also changed the metering rod springs. Very easy to do. Start with the springs. Also have you pulled any plugs to check for lean? 

I do have the kit (#1489) and did try opening up the jets last year.  I also recall changing rods to richen up a bit.  No improvement but may not have been changing the right parts.  I didn't mess with the spring, however, so that's something I could try.  Which way would you go with them?  Towards lower in. Hg?  I've attached a picture of the springs below.  I think I have the colors correct but if you could confirm, that would be great.  From left to right, Blue (3"), Yellow (4"), Orange (5"), Pink (7"), Silver (8").

Regarding the plugs, they don't look lean to me.  Actually look okay.  See pictures below.

Thanks for your help.

Mine has the pink springs, maybe give them a try.

[BSB67]

I keep revisiting this post, and cannot help thinking there is something else we're missing.

Can you step back and give us a little history.  How long you've had it, how much you drive it, when did the problem start, has it always had a problem, what things have you done, are there any operating conditions that are okay, how does it idle....etc.

[CRW-FK5]

I keep revisiting this post, and cannot help thinking there is something else we're missing.

Can you step back and give us a little history.  How long you've had it, how much you drive it, when did the problem start, has it always had a problem, what things have you done, are there any operating conditions that are okay, how does it idle....etc.

Sure.  I have owned the car since February of '15.  I do drive it often, taking it to store on errands, etc...  The car idles okay but does have a higher street cam so some roughness is expected.  The car did not have the problem until around June of that year.  At that time I noticed when I got on it hard there was a significant stumble that only stopped when I backed off.  I had done nothing to the car prior to that that could be linked to it.  Nothing to engine.

The problem persisted and late last year I decided to buy the Edelbrock calibration kit to see if I could play around with jetting on the 750 (#1411) carb to try and cure it.  I tried larger jets in secondaries and smaller rods in primaries (I believe) but problem did not change.

Next I replaced fuel pump and filter, as they were fairly inexpensive.  No effect on condition.

Later on in the season I decided to swap carbs from the 750 cfm Edelbrock #1411 to a 600 cfm Edelbrock #1406 that a friend had laying around, just to see if the problem changed or went away.  It was an easy way to try and find the root cause.  As I mentioned, I did this late in the season so ambient temps were cool.  When I installed this and tested it the problem was gone.  I made sure the car was warmed up and tried several times, each time the bog or stumble was gone.  I then reinstalled the 750 and took it back out under exact same outside air temps and vehicle temps (done within 20 minutes of test with friends 600 cfm carb installed).  Immediately the bog / stumble was back.  I then believed that the issue was in the 750 carb, somewhere.  

Then I took the 750 carb and took it apart and cleaned it, blowing out passages, etc...  I also replaced the jet/rod configuration to what was installed when I got the car and confirmed they were to the recommended configuration in the Edelbrock guide, which they were.  I took the car out again (same day under same conditions) and the bog was gone.  At that point I believed the problem was solved and that perhaps I somehow had some dirt in the carb somewhere that was cleaned out during the R&R.  Since it was late in the season I put the car away for the winter content (so I thought) that the problem was solved.  

So this spring when I got the car out I found that the problem was back, and actually seemed a bit worse.  Outside temps were cool, similar to what they were late last season, so I do not believe that was the variable.  When I say worse, I mean now I just have to accelerate lightly and the stumble is there.  Before I had to really get into it.  So I swapped the same Edelbrock 600 back on, hoping I would see the same thing I did last year where the problem went away.  Instead, the problem continued.  So now it stumbles with either carb on it.

I know somewhere in the season last year (after the problem was found) I messed with the timing (using a timing light).  I just don't recall where it was but thought it was reading "after TDC", which did seem very odd.  I recall readjusting it but later going back in and readjusting again, thinking I may have had the zeroing dial on the light set accidently at some value other than zero when I read it before, causing me to think it was timed at a different degree than it actually was.  I have since confirmed that the ignition timing is set correctly (see above post).

I do have an AFR meter now installed and took the car out a few days ago.  Idling somewhat cold I am at between 12.7 -13.2, although it bounces around some.  At around 2,000 rpm (again somewhat cold) I am at 10.8 - 11.3.  Those seemed to be the ranges.  When warm and crusing maybe 1,500 rpm I am at 11.8 - 12.0, but when I then drop down a gear and accelerate moderately hard it steadily gets leaner peaking at 17.3 before I back off.  Another attempt I felt it begin to bog when it got to 13.8.  I have fairly new gas in it but could be some left over from last season and could be winter blend (although same gas as I had in it when testing late in season last year).  I have added 2 gallons of 110 racing fuel to try and get rid of pinging.  This did seem to help address that.

As mentioned above, I have had distributor out and disassembled.  No broken parts, springs, etc...  I have run compression test with good consistency between cylinders.  I have run leakdown test but believe the gauge was malfunctioning since repeated readings on same cylinder yielded varying results.  I did confirm in this test that valves are tight to the head and only loss is through rings.  I hear strong air hissing beneath the intake manifold area but believe it is the same sound from air blowing by rings and through block.  Leakage sound is identical for all cylinders.  Plugs were checked and seem fine.

I also checked angular play in the valve train, coming up with around 3.5°.  I did this by turning crank while watching distributor rotor and noting crank rotation when rotor just started to move.  At first I was at around 8° but noticed part of that was the play between distributor tab and gear slot.  So rechecking with this rotated to take up play I got around the 3.5° chain play.  This may seem like a lot but not sure it explains the severe bog I'm getting.

So this is pretty much where I sit today.  My next step is to try and go with different springs in the carb but can't help knowing that the car ran fine originally and that something changed, so any modifications to carb set up would either be unsuccessful or masking the root cause.  The timing oddity still makes me wonder about the whole thing.  Does it make sense that the timing light was reading ATDC?  Could that have been an indication that the chain had jumped a tooth?  I may have to explore that a bit more.

I really appreciate the help.  Thanks, all.

[BSB67]

Your problem is in the carb.  Fine tuning is not what is needed at this point, IMO.  You have a problem, you just need to find it.

[XH29N0G]

The others who are advising you know more than me so their comments should take precedence over mine, but in reading your description I have an observation and a question.

The observation:  If your air fuel is going to 17 and staying there on hard acceleration (rather than dropping back to ~13), you could have an issue with the main jets.  That could explain part of the issue with hard acceleration.  I think it should be in the 12-13 range for acceleration.  Also is the miss and bog in a specific rpm range and in all gears?

I also was curious where your timing is set (for idle and for total advance).

I also see you have a purple shaft cam, which one?  Am I correct in inferring that you have a manual transmission? 

[CRW-FK5]

.

[CRW-FK5]

The others who are advising you know more than me so their comments should take precedence over mine, but in reading your description I have an observation and a question.

The observation:  If your air fuel is going to 17 and staying there on hard acceleration (rather than dropping back to ~13), you could have an issue with the main jets.  That could explain part of the issue with hard acceleration.  I think it should be in the 12-13 range for acceleration.  Also is the miss and bog in a specific rpm range and in all gears?

I also was curious where your timing is set (for idle and for total advance).

I also see you have a purple shaft cam, which one?  Am I correct in inferring that you have a manual transmission? 

Thanks.  Agreed on the AFR.  Something appears to be allowing for a lean condition under load.  Since it's pretty easy to try richening up the mains, I will try that.  It's tough because I keep going back to the fact that I have the same carb set up as when I bought it and something seems to have changed in the performance.  Changing the jets, rods, springs to get it to run right seems a little like compensation for some other root cause.  But at this point I appear to have a lean condition under load and since there are quick & easy adjustments (springs, rods, jets) I can make to hopefully affect the mixture, I guess it makes sense to go down that road for now.

The bog seems to be under load at any range above, say, 2,000 rpm.  Just guessing.

For timing, I believe I'm set at a conservative 2° BTDC.  I have not checked total yet, but currently have vacuum advance disconnected.  Will check.

I am not sure on the cam.  When I had the distributor out I peeked in at the cam and could see it had purple paint between lobes at the front, so I am assuming it is some type of Purple Shaft cam.  And yes, it is an A833 manual trans. car.

[CRW-FK5]

You need to richen up the edelbrock, I had to do mine. Same problem you are having. Most edlebrocks are lean from the factory. Buy the strip kit it has everything you need. Mine had to go up 2 jet sizes on the primary and I think down on the metering rods. Also changed the metering rod springs. Very easy to do. Start with the springs. Also have you pulled any plugs to check for lean? 

I do have the kit (#1489) and did try opening up the jets last year.  I also recall changing rods to richen up a bit.  No improvement but may not have been changing the right parts.  I didn't mess with the spring, however, so that's something I could try.  Which way would you go with them?  Towards lower in. Hg?  I've attached a picture of the springs below.  I think I have the colors correct but if you could confirm, that would be great.  From left to right, Blue (3"), Yellow (4"), Orange (5"), Pink (7"), Silver (8").

Regarding the plugs, they don't look lean to me.  Actually look okay.  See pictures below.

Thanks for your help.

Mine has the pink springs, maybe give them a try.

Thanks.  Will give them a try.

[XH29N0G]

See what the total timing is. I realize 0+/-2 degrees BTDC is what the stock 440's were set, but you may find that timing can be advanced, especially given you have a different cam.  This can affect idle quality and also the behavior of the engine.  In the long term (not now since you had a pinging issue) I suggest setting the advance at idle for the best quality idle (highest vacuum, smoothest, maybe less rich).  This may put your total advance too high (which could cause the ping you are seeing), but that can be addressed once you know where you want the idle set.

The first thing I would do would be to see if you can fix the lean condition on acceleration.  I think that could be a big part of the problem.

You mention this issue not being there, then starting and then getting worse.  I do not know why that would be, but I would get the fuel system set first.

2000 RPM might be low for some of the acceleration tests, some engines don't really settle in until higher. 

[CRW-FK5]

Just tried different springs in carb (pink) and smaller rods 7547's changed to 7537's.  Still get terrible bog.  Cruising in 4th I'm at 10.9-11.4 AFR.  Accelerating approx. half throttle in 4th starts bogging at mid 12's then jumps to 15 plus (maybe in reaction to bogging and not actually initiating it).  Tried again in 1st gear. Steady at around 11.9 AFR.  Under mid throttle hits 12.9, then 13.9, then jumps to 21.2 on meter combined with bogging.  It goes from accelerating to making no power during bogging.  Almost like a clutch slipping feel (for comparison).

[XH29N0G]

A few further questions.

Is the accelerator pump working?  And starting to squirt as soon as the throttle moves?

Is the high A/F something that is sustained and continues if you keep accelerating or does the A/F recover at higher RPM. 

If you are at 3500 RPM or 4500 RPM cruising is the A/F always this high.  I would be worried if it were this high and would be careful if it were in the 16+ range.
   

[CRW-FK5]

A few further questions.

Is the accelerator pump working?  And starting to squirt as soon as the throttle moves?

Is the high A/F something that is sustained and continues if you keep accelerating or does the A/F recover at higher RPM.  

If you are at 3500 RPM or 4500 RPM cruising is the A/F always this high.  I would be worried if it were this high and would be careful if it were in the 16+ range.
   

The accelerator pump is working.  It may not be in optimal position (hole) but is functional and looks good.

I believe as long as I accelerate slowly (hardly opened throttle position) the A/F ratio will remain on rich side (between 12 and 13 range).  I have not tested this but based on my observation at lower sustained RPM's I believe this would be the case.  I can run through that to confirm.  Seems like under moderate acceleration the A/F ratio leans out from rich to the point where bogging occurs.  It is difficult to establish the A/F ratio when this begins because the high lean spikes (17+) that I'm seeing may actually be an effect of the bogging and not the root cause.  Kind of like having an immediate lean condition  when you take your foot off the gas.  In other words, the actually bogging may be occurring at around 14 A/F ratio, but the resultant bogging might then be creating the higher lean spikes I'm seeing on my meter.  I may try and record an acceleration run with the card so I can see exactly what's happening.  Right now I'm recording the display with my phone and viewing afterwords.  From this, I see the high lean conditions flash on the screen but it's real hard to establish time sequence relative to point when actual bog occurs.

[c00nhunterjoe]

Ok, now im confused. Your 1st post said you swapped carbs and it made NO difference. Now you just posted that YES it fixed the problem and putting yours back on made the problems come back. That means your carb is the problem.

[XH29N0G]

I just saw c00nhunter's post and I also missed the comment about the carb swap making a difference.  I think those who have pointed to the carb are right.

May I suggest a few more tests.    I think you want to figure out what the baseline settings should be.  [I also think that finding a way to log the A/F will help.  I am using an innovate gauge and feed it out to an RS232 and then an RS232 to USB adapter that allows me to plug into my laptop and read using their logworks software.  You might be able to do the same.]

• I would test the A/F at steady throttle at 3500 and 4500 RPM just to get that information.
  
  
  
• If the A/F under those conditions look OK (could be 12,13, 14, but not 16, 17, 18, or 11, 10,9) I would then check to see if the A/F recovers once the car settles in to accelerating, e.g., after the bog and lean spot have happened.

I am not using an edelbrock so I don't know if what I am about to describe is relevant.  

I see the A/F spike to lean condition when I hit the throttle because the throttle blades open letting in a bunch of air, and then it goes to slight rich because of the accelerator pump, and then once the main jets kick in it settles to about 12.8-13.2 all the way up to 5500 RPM.  I had bog/hesitation when the spike was larger (higher) because the pump shot was too small or too late, or when the drop in AF was very low (because the pump shot was too big). Ultimately I found a Goldilocks situation by adjusting the amount and timing of the pump shot.  I also found that the problem was less pronounced when I started the acceleration runs at higher RPM (like 3500 instead of 2500).  Starting at 2000 is asking too much of my car.  I am also running a manual transmission and I think an automatic would downshift under those conditions but the manual will just lug the engine.  

I wonder if there is an adjustment like the pump shot adjustment I do that you can do with the Edelbrock.  If so, and if your idle, cruise and WOT A/F look OK, I would look to the pump shot for a solution.

[funknut]

Ok, now im confused. Your 1st post said you swapped carbs and it made NO difference. Now you just posted that YES it fixed the problem and putting yours back on made the problems come back. That means your carb is the problem.

I read his posts a couple times and I think this is the timeline he lays out.  Please correct me if/where I'm wrong:

Summer/Fall 2015:
- bog/stumble was first noticed
- changed jets/rods in the 750, no change
- replaced fuel pump and filter, no change
- swapped out 750 for 600cfm carb, stumble goes away
- reinstalled 750, problem returns
- took apart the 750, cleaned it and returned it to original jet/rod configuration
- reinstalled 750, problem is gone
- at some point during this season, he 'messed with the timing'
- car put away for the winter

Spring 2016
- bog/stumble appears w/ 750
- again swapped out 750 for same 600cfm carb as previous year, problem persists

[CRW-FK5]

Ok, now im confused. Your 1st post said you swapped carbs and it made NO difference. Now you just posted that YES it fixed the problem and putting yours back on made the problems come back. That means your carb is the problem.

I read his posts a couple times and I think this is the timeline he lays out.  Please correct me if/where I'm wrong:

Summer/Fall 2015:
- bog/stumble was first noticed
- changed jets/rods in the 750, no change
- replaced fuel pump and filter, no change
- swapped out 750 for 600cfm carb, stumble goes away
- reinstalled 750, problem returns
- took apart the 750, cleaned it and returned it to original jet/rod configuration
- reinstalled 750, problem is gone
- at some point during this season, he 'messed with the timing'
- car put away for the winter

Spring 2016
- bog/stumble appears w/ 750
- again swapped out 750 for same 600cfm carb as previous year, problem persists

Thanks.  Yes, that is correct chronology.  For clarification, the timing adjustments did occur before the carb swap last year.

The return of the problem this season along with the failure of the problem to go away, after similar carb swap last year, was not expected, and had me completely confused.

[CRW-FK5]

Ok, now im confused. Your 1st post said you swapped carbs and it made NO difference. Now you just posted that YES it fixed the problem and putting yours back on made the problems come back. That means your carb is the problem.

Yes, I can see where that might have been confusing.  In my first post I failed to provide full history of events leading up to my recent activities.  In total there were 2 carb swaps done, one late last year and one again this year.  The first time the problem went away, indicating the carb was the problem.  When the problem returned this year I performed similar carb swap and surprisingly found that the problem did not go away.  This was not expected, and why I decided to post here.  Sorry for the confusion.

[CRW-FK5]

I just saw c00nhunter's post and I also missed the comment about the carb swap making a difference.  I think those who have pointed to the carb are right.

May I suggest a few more tests.    I think you want to figure out what the baseline settings should be.  [I also think that finding a way to log the A/F will help.  I am using an innovate gauge and feed it out to an RS232 and then an RS232 to USB adapter that allows me to plug into my laptop and read using their logworks software.  You might be able to do the same.]

• I would test the A/F at steady throttle at 3500 and 4500 RPM just to get that information.
  
  
  
• If the A/F under those conditions look OK (could be 12,13, 14, but not 16, 17, 18, or 11, 10,9) I would then check to see if the A/F recovers once the car settles in to accelerating, e.g., after the bog and lean spot have happened.

I am not using an edelbrock so I don't know if what I am about to describe is relevant.  

I see the A/F spike to lean condition when I hit the throttle because the throttle blades open letting in a bunch of air, and then it goes to slight rich because of the accelerator pump, and then once the main jets kick in it settles to about 12.8-13.2 all the way up to 5500 RPM.  I had bog/hesitation when the spike was larger (higher) because the pump shot was too small or too late, or when the drop in AF was very low (because the pump shot was too big). Ultimately I found a Goldilocks situation by adjusting the amount and timing of the pump shot.  I also found that the problem was less pronounced when I started the acceleration runs at higher RPM (like 3500 instead of 2500).  Starting at 2000 is asking too much of my car.  I am also running a manual transmission and I think an automatic would downshift under those conditions but the manual will just lug the engine.  

I wonder if there is an adjustment like the pump shot adjustment I do that you can do with the Edelbrock.  If so, and if your idle, cruise and WOT A/F look OK, I would look to the pump shot for a solution.

Thanks for the detailed advise and recommendations.  I'll work on gathering the data you've suggested.  Seems to be an agreement that the problem is fuel related and not spark related.  

[XH29N0G]

Ok, now im confused. Your 1st post said you swapped carbs and it made NO difference. Now you just posted that YES it fixed the problem and putting yours back on made the problems come back. That means your carb is the problem.

Yes, I can see where that might have been confusing.  In my first post I failed to provide full history of events leading up to my recent activities.  In total there were 2 carb swaps done, one late last year and one again this year.  The first time the problem went away, indicating the carb was the problem.  When the problem returned this year I performed similar carb swap and surprisingly found that the problem did not go away.  This was not expected, and why I decided to post here.  Sorry for the confusion.

Was the first time in summer and second time in winter?  Could be the gas was not set up for the winter on the 600 cfm carb.

[c00nhunterjoe]

How long has your "known good carb" been sitting on the shelf before you tested it on your car? If you are 100% sure the carb you swapped is good, and the meter shows way lean on both carbs and changing metering and jets has no effect as stated, then either your fuel pump is bad or your fuel lump pushrod is shot, or both.

[c00nhunterjoe]

Ok, now im confused. Your 1st post said you swapped carbs and it made NO difference. Now you just posted that YES it fixed the problem and putting yours back on made the problems come back. That means your carb is the problem.

Yes, I can see where that might have been confusing.  In my first post I failed to provide full history of events leading up to my recent activities.  In total there were 2 carb swaps done, one late last year and one again this year.  The first time the problem went away, indicating the carb was the problem.  When the problem returned this year I performed similar carb swap and surprisingly found that the problem did not go away.  This was not expected, and why I decided to post here.  Sorry for the confusion.

Was the first time in summer and second time in winter?  Could be the gas was not set up for the winter on the 600 cfm carb.

I do not change any carb settings from 100° summer days to 30° winters. Nobody in the 60s when these cars were new had to rejet and meter their cars for the seasons either.

[CRW-FK5]

How long has your "known good carb" been sitting on the shelf before you tested it on your car? If you are 100% sure the carb you swapped is good, and the meter shows way lean on both carbs and changing metering and jets has no effect as stated, then either your fuel pump is bad or your fuel lump pushrod is shot, or both.

Thanks.  Keep in mind that what I originally thought was a "known good carb" turned out to not be the case when I had to again swap it in because the problem came back again this season.  I have only checked A/F on the 750 that was on the car when I bought it, but based on similar behavior with both carbs now, I suspect I would also see lean condition on A/F meter with the 600 if I put it back on.  

To you question/suggestion on fuel pump or push rod, shouldn't there be enough fuel in the bowls for the engine to run off of immediately, resulting in good acceleration right away but then turning into stumbling once fuel demand exceeded what was in the bowls?  In my case, I get stumbling right away which seems (to me at least) that it is not a fuel pump, filter, push rod problem.  If I'm off base on this let me know.  The one thing I did not check when I had the pump out was the length of the push rod.  I do wish I had done that.  FYI - float levels are okay.

[CRW-FK5]

I just saw c00nhunter's post and I also missed the comment about the carb swap making a difference.  I think those who have pointed to the carb are right.

May I suggest a few more tests.    I think you want to figure out what the baseline settings should be.  [I also think that finding a way to log the A/F will help.  I am using an innovate gauge and feed it out to an RS232 and then an RS232 to USB adapter that allows me to plug into my laptop and read using their logworks software.  You might be able to do the same.]

• I would test the A/F at steady throttle at 3500 and 4500 RPM just to get that information.
  
  
  
• If the A/F under those conditions look OK (could be 12,13, 14, but not 16, 17, 18, or 11, 10,9) I would then check to see if the A/F recovers once the car settles in to accelerating, e.g., after the bog and lean spot have happened.

I am not using an edelbrock so I don't know if what I am about to describe is relevant.  

I see the A/F spike to lean condition when I hit the throttle because the throttle blades open letting in a bunch of air, and then it goes to slight rich because of the accelerator pump, and then once the main jets kick in it settles to about 12.8-13.2 all the way up to 5500 RPM.  I had bog/hesitation when the spike was larger (higher) because the pump shot was too small or too late, or when the drop in AF was very low (because the pump shot was too big). Ultimately I found a Goldilocks situation by adjusting the amount and timing of the pump shot.  I also found that the problem was less pronounced when I started the acceleration runs at higher RPM (like 3500 instead of 2500).  Starting at 2000 is asking too much of my car.  I am also running a manual transmission and I think an automatic would downshift under those conditions but the manual will just lug the engine.  

I wonder if there is an adjustment like the pump shot adjustment I do that you can do with the Edelbrock.  If so, and if your idle, cruise and WOT A/F look OK, I would look to the pump shot for a solution.

I have the Innovate LM-2 with an SD card for gathering data, so I can record directly onto the card during test runs.  I then have to download that data to my computer and try and generate charts and plots.  Your way seems a bit more straight forward. I don't have an RS232 port but do have a cable that will connect vis USB.  I have not tried to connect this way directly when gathering data.  Do you know if that will work (see pictures below)?

[XH29N0G]

I think what you have works as well or better than what I am doing.  I just bought the innovate gauge kit with the LC-2.  It came with a serial cable (I was wrong about RS232) but no other way to log.  I needed the serial to USB to hook it to my computer which probably runs similar software to what you run (Logworks).  I would like to have the set up you have.

[CRW-FK5]

Here are my charts.  I was not able to complete (or even attempt) runs at 4,500 based on the difficulty I had at 3,500, so was only able to get charts at 3,500.  I did 2 passes, one in 3rd gear at 3,500 (Session #1) and one in 1st gear at 3,500 (Session #2).  Both resulted in heavy stumbling and looks like severe lean condition.  Then for comparison I ran a couple of other runs.  I've added notes to the sessions regarding observations noted during the runs.  The only one that has me confused is Session #7 when I started off cruising at 30 MPH in 4th and then accelerated approx. half throttle (not shifting down).  During the acceleration I noticed the hesitation and stumbling, but when I looked at my A/F ratio it was actually running rich.  I did not expect that.  

Anyway, any feedback would be greatly appreciated.

[CRW-FK5]

Remaining Sessions.

[XH29N0G]

CRW-FK5,  I think these A/F traces can potentially lead others to help.  I have not worked with edelbrock carburetors so will not be of much help.  I imagine the principles are similar, but understand the design is different.  My understanding of the principles is that the carburetors have to meter the right amount of gas at idle, at cruise, and under hard acceleration.  (I usually do not start acceleration runs under 2500 to 3000 RPM because of worries about straining the engine.).  I believe you have the idle circuit set correctly, and the cruise circuit.  It looks to me like you have a problem with the main circuit (the higher RPM and acceleration) and possibly with the transition to acceleration (accelerator pump).  
The only thing I have done in addition to this is a hard acceleration run from ~3000 to ~5300 RPM in 2nd or 3rd.  This is just to see what the  A/F settles down to.  I am guessing what you have is what will be needed for someone here to make very specific suggestions about changes from the set up you currently have.

If you do not get a response on this thread in short order, I suggest starting a new thread with the A/F charts asking for help on dialing in an edelbrock carburetor.  I am sure others will be interested and setting it up as a separate thread also will help people find it.  There may be an old thread about it, but I cannot find it.

[Mebsuta]

I flattened a lobe on a camshaft one time.   It would idle okay but would start backfiring through the carburetor when you tried to drive it, especially accelerating.  

I have had coils go bad, and the car would want to stall at low speed, like when you were crawling through a parking lot. 

[funknut]

If you just rev the engine to 3500 or 4500 RPM (where you were seeing the lean condition) in park or neutral (no load on the engine) what happens?

Do you have a fuel pressure gauge you can use to diagnose whether or not you are getting enough fuel to the carb in the first place?

You have the same problem with 2 different carburetors, it's possible that it's the carb tuning, but it's also possible if not likely that the fuel delivery is where the problem lies.

How long has your "known good carb" been sitting on the shelf before you tested it on your car? If you are 100% sure the carb you swapped is good, and the meter shows way lean on both carbs and changing metering and jets has no effect as stated, then either your fuel pump is bad or your fuel lump pushrod is shot, or both.

[CRW-FK5]

If you just rev the engine to 3500 or 4500 RPM (where you were seeing the lean condition) in park or neutral (no load on the engine) what happens?

Do you have a fuel pressure gauge you can use to diagnose whether or not you are getting enough fuel to the carb in the first place?

You have the same problem with 2 different carburetors, it's possible that it's the carb tuning, but it's also possible if not likely that the fuel delivery is where the problem lies.

How long has your "known good carb" been sitting on the shelf before you tested it on your car? If you are 100% sure the carb you swapped is good, and the meter shows way lean on both carbs and changing metering and jets has no effect as stated, then either your fuel pump is bad or your fuel lump pushrod is shot, or both.

I don't have a fuel pressure gauge but may have to get one.  Will flow rate be sufficient for diagnosis?  I will try tomorrow to measure A/F in neutral at 3,500 & 4,500. 

[CRW-FK5]

Here are my results from the 2 sessions in neutral at high RPM (3,500 & 4,500).  No hesitation, bogging, backfiring, stumbling whatsoever.  Very smooth.  A/F ratio confirmed good, as well.