It is stumbling only under hard acceleration and while driving

[johnnycharger]

Hi Guys
Got my charger back on the road but it is having a stumbling issue. It started stumbling only if I mash the pedal and only while in gear driving. If I have it in park I can rev the snot out of it and it is fine. I noticed gas leaking from the front driver's side of the carb so I replaced the accelerator pump diaphragm which fixed the leak but not the stumbling. Any guesses?

[Kern Dog]

I have seen this happen when the ignition system is not working 100%. The increased demand under a load resulted in misfires.
My brother had a slant six '78 D 100 that idled great but popped and stumbled when in gear while accelerating. New spark plug wires changed everything.
This may not be your problem but it is worth a look.
Good luck...Report back with whatever happens.

[XH29N0G]

I had the same experience as KD with ignition related issues, but since you also said you messed with the accelerator pump, I would also check that out.  The key is that you know the car was dialed in before you put it up for a rest.

[Canadian1968]

First thing first. Make sure the accel. pump is adjusted correctly !

The car was running fine before the pump replacement?

[johnnycharger]

Hi guys
Thanks for the suggestions. Car was parked for a bit and ran great before. Just before finishing the front end rebuild the fuel pump died. I replaced that as well as my spark plugs, fuel filter and then the accelerator pump once I saw it leaking. I will double check the plug wires are on right and I will check the adjustment of the accelerator pump.

[XH29N0G]

A quick question.  After you mash the pedal and it stumbles, does it recover and accelerate, or does it just stumble.

[johnnycharger]

It does not recover. If I don't let off I am certain it will stall.

[XH29N0G]

IF it doesn't recover, I think that might be a clue and someone else here will be better at diagnosing than me.  Do you know that the right amount/pressure of fuel is making it to your carburetor?  

You mention replacing the fuel pump.  Was it a mechanical one? If so, did you check the pushrod when you replaced it?  

I had the pushrod wear down on my fuel pump and the car would just die when I applied gas.  I had an A/F gauge so I had a clue about why.  To confirm, I installed a fuel pressure gauge into the system, taped it to the windshield and drove around.  Wait to see if someone else has a recommendation.

[Kern Dog]

Over the summer I had the car down for a new heater and A/C system installation. I was doing different things as well so the whole deal took a few months. By October the car was real hard to start and keep running so I suspected the carburetor was to blame after switching distributors, coils, electronic ECUs did no good. After a carburetor rebuild, I drained the gas and added new 91 octane gas. The car ran fine afterwards so I suspect that all along, the gas had just gone bad. I had a full tank in November 2018 and hadn't driven the car much in 2019. The California gasoline does NOT stay potent for that long. My lower compression engines will run on old gas but my Charger seems to need a fresh mix to run right.

[johnnycharger]

IF it doesn't recover, I think that might be a clue and someone else here will be better at diagnosing than me.  Do you know that the right amount/pressure of fuel is making it to your carburetor?  

You mention replacing the fuel pump.  Was it a mechanical one? If so, did you check the pushrod when you replaced it?  

I had the pushrod wear down on my fuel pump and the car would just die when I applied gas.  I had an A/F gauge so I had a clue about why.  To confirm, I installed a fuel pressure gauge into the system, taped it to the windshield and drove around.  Wait to see if someone else has a recommendation.

Good point. I did measure the push rod while it was out because I recalled hearing about that.

[johnnycharger]

Over the summer I had the car down for a new heater and A/C system installation. I was doing different things as well so the whole deal took a few months. By October the car was real hard to start and keep running so I suspected the carburetor was to blame after switching distributors, coils, electronic ECUs did no good. After a carburetor rebuild, I drained the gas and added new 91 octane gas. The car ran fine afterwards so I suspect that all along, the gas had just gone bad. I had a full tank in November 2018 and hadn't driven the car much in 2019. The California gasoline does NOT stay potent for that long. My lower compression engines will run on old gas but my Charger seems to need a fresh mix to run right.

That is true our gas does suck. I don't think my problem at the moment is bad gas though because it runs fine with no load on it. I can rev it up like an 18 year old with a mullet and it doesn't skip a beat....

[metallicareload99]

Is the check valve for the accelerator pump installed, and did you use the bowel gaskets with the passage in it for the accelerator pump?

[johnnycharger]

I only swapped out the rubber gasket part with the metallic disk.

[johnnycharger]

The pump was set too tight. I set it correctly and hopefully that will solve it. I can test drive her because it is raining now.

[XH29N0G]

Sounds good. 

[johnnycharger]

Still is the same 🤔

[XH29N0G]

Some more questions. 

How long did the car sit since the last time it ran right?

What type of carburetor do you have?

Are there any other symptoms?

I think if you see a good healthy pulse of gas from the accelerator pump nozzle into the barrels that starts as soon as the throttle is pushed, then that should be OK. 

[johnnycharger]

Some more questions. 

How long did the car sit since the last time it ran right? Car was parked for over a year. I ran it every month and it always fired up instantly. Still does.

What type of carburetor do you have? Holley 750 double pumper

Are there any other symptoms? No. Car starts right away. Sounds great if l rev it in the driveway. Fails consistently under hard acceleration.

I think if you see a good healthy pulse of gas from the accelerator pump nozzle into the barrels that starts as soon as the throttle is pushed, then that should be OK.  Looks like it is indeed spraying a lot of gas when I push on the pump.

I really appreciate the help.

[XH29N0G]

I asked about how long it sat as a long shot that something else like varnish might be blocking the jets.  The things I can think of are:

1. The ignition or gas as KD suggests. 

2. Something with the carburetor.  For carburetor tests, I would check easy things first.
    2.a. You say the accelerator pump works, but a mechanical secondary, has two accelerator pumps and two squirters. Are both working? 
    2.b. After that, I might try disconnecting the linkage between secondaries and primaries so it runs only on the primaries and seeing if there is any change.
          If there is a change, then I would consider focusing on something with the carburetor and probably the secondaries. 
          If not, I would verify that enough fuel is making it to the carburetor, check float levels, and fuel pressure.  Then I would start looking again to ignition and check everything I   
          could think of that might be a culprit (gas, vacuum, timing - do you run a vacuum advance or mechanical advance?  And are you using electronic ignition or points?). 

It is not difficult to pull the bowl and metering plate off to see if there is anything obvious that was blocked with the passages, but you will need gaskets, and I would hold off. I'm hoping it will be something simple because I find the more things I try, the more likely I am to create another problem. 

[johnnycharger]

Thank you so much for the suggestions. I will try some today.
I also re read the instructions on adjustment of the accelerator pump and think that I may have got it wrong. I missed the step of disengaging the fast idle cam lever. So I am going to start by trying to figure out how to do that.
I really appreciate the help and support while I try to sort this out.

[lukedukem]

Hi Guys
Got my charger back on the road but it is having a stumbling issue. It started stumbling only if I mash the pedal and only while in gear driving. If I have it in park I can rev the snot out of it and it is fine. I noticed gas leaking from the front driver's side of the carb so I replaced the accelerator pump diaphragm which fixed the leak but not the stumbling. Any guesses?

what gear are you in. this might sound dumb but if your transmission kickdown isn't working properly and you mash it in 3rd gear you flood the engine with gas and if your not up to higher rpm then it boggs it down. hope that sounds right. if you try to drive it manually does it still do it?
I didn't ask if its and auto or manual. if its manual then ignore this. wild hunch, might sounds stupid but i'd rather sound dumb then not say anything to help

Luke

[johnnycharger]

Hi Luke
It is an automatic. Good points. I will try manual shifting today and I will pay attention to if it is gear specific.

[johnnycharger]

Ok, so it is definitely more prevalent in 2nd and 3rd. I adjusted the kick down further and that didn't fix it. Did some YouTube searching and found out about the paperclip trick to check the vacuum secondary. I checked it and the paperclip did not move. I tried it by hand and it sounds really weird to me but I have not ever checked one before. Here is a video of the noise.
https://youtu.be/n1stpw523FE
I am thinking the diaphragm is bad.

[XH29N0G]

I am not sure if that sounds strange or not.  There is a diaphragm that will compress, and I believe it will do so when you move it like you did.  That could be the noise. 

I also do not think that the vacuum secondary not opening would cause it to fall flat.  My reasoning is twofold. First,  I can drive in a quite spirited ways after diabling the secondaries on my car. Second, I had an old two barrel car and it did not fall flat when I floored it. 

I wonder if the secondaries are not opening is a consequence of the issue you are facing rather than the cause of it.  I thought that secondaries open when the flow through the primaries is high enough to draw a vacuum on some orifice connected to that vacuum pot. So I would think with the engine stumbling that it is not pulling a lot of air and therefore not likely to open the secondaries fully if at all.

[Kern Dog]

I can rev it up like an 18 year old with a mullet and it doesn't skip a beat....

Nobody called you on this but I noticed it. Funny stuff!
Carburetors ......If you are willing to drive,  I'd let you try one of mine that was recently rebuilt. I also have a  ThermoQuad that was rebuilt a year ago but has been in a box since then. You'd have to drive past Sacramento to get it . Whether that is worth your time or not, that is up to you.

[johnnycharger]

I am not sure if that sounds strange or not.  There is a diaphragm that will compress, and I believe it will do so when you move it like you did.  That could be the noise. 

I also do not think that the vacuum secondary not opening would cause it to fall flat.  My reasoning is twofold. First,  I can drive in a quite spirited ways after diabling the secondaries on my car. Second, I had an old two barrel car and it did not fall flat when I floored it. 

I wonder if the secondaries are not opening is a consequence of the issue you are facing rather than the cause of it.  I thought that secondaries open when the flow through the primaries is high enough to draw a vacuum on some orifice connected to that vacuum pot. So I would think with the engine stumbling that it is not pulling a lot of air and therefore not likely to open the secondaries fully if at all.

I think you are right. That really makes sense. Thank you.

[johnnycharger]

I can rev it up like an 18 year old with a mullet and it doesn't skip a beat....

Nobody called you on this but I noticed it. Funny stuff!
Carburetors ......If you are willing to drive,  I'd let you try one of mine that was recently rebuilt. I also have a  ThermoQuad that was rebuilt a year ago but has been in a box since then. You'd have to drive past Sacramento to get it . Whether that is worth your time or not, that is up to you.

I knew you would catch that one🤣.
I really appreciate the offer. Thank you very much. I may take you up on it but I still want to try a few things first. 👍👍👍

[Canadian1968]

Watched the video. That sounds fine. You are hearing the diaphragm in the secondary canister being compressed and released . Did you remove the accelerator pump cam at all when you changed the inner gasket ? did you do the change on the car or did you remove the carb ?

Another way to test is to actually disengage the secondaries.  The car should run fine on only the primaries until  you get to your higher rpm (4000 + rpm )  when you reach the limits of the primary alone . Even then you just notice lack of power it should not fall on its face or stumble

Have you checked your float levels as well ?

[Kern Dog]

Float levels...I should have mentioned that.
I had a fuel starvation problem where the car ran fine at cruise but would sometimes starve out on hard acceleration. The fuel pump must have been going bad because the clear filter would show hardly any fuel in it sometimes. The pushrod was fine. I switched to a Carter HV pump and a regulator and since then, no problems PLUS no vapor lock like I'd sometimes have. The regulator has a return line to the tank so the gas runs either to the carb or back to the tank.

[johnnycharger]

Watched the video. That sounds fine. You are hearing the diaphragm in the secondary canister being compressed and released . Did you remove the accelerator pump cam at all when you changed the inner gasket ? did you do the change on the car or did you remove the carb ?

Another way to test is to actually disengage the secondaries.  The car should run fine on only the primaries until  you get to your higher rpm (4000 + rpm )  when you reach the limits of the primary alone . Even then you just notice lack of power it should not fall on its face or stumble

Have you checked your float levels as well ?

I changed the accelerator pump on the car. Just the diaphragm.

[johnnycharger]

Float levels...I should have mentioned that.
I had a fuel starvation problem where the car ran fine at cruise but would sometimes starve out on hard acceleration. The fuel pump must have been going bad because the clear filter would show hardly any fuel in it sometimes. The pushrod was fine. I switched to a Carter HV pump and a regulator and since then, no problems PLUS no vapor lock like I'd sometimes have. The regulator has a return line to the tank so the gas runs either to the carb or back to the tank.

I started second guessing the pump so I reread everything and my pump was spec at 5psi. Holley told me the carb needed 6psi so I ordered another one at 6psi. Just installed it and it did not fix it. I does seem to have made a very slight improvement but I don't know if I am just over analyzing it now.

[johnnycharger]

I adjusted the floats that were too full made no change.
I disconnected the secondary again no change

[XH29N0G]

Im flummoxed.

It sounds like you have some information.
Fuel level is OK. 
The squirt through the nozzles is fine - you see it come out as soon as you move the throttle and the pump shot lasts for about 0.5 to 1.5 seconds - correct?
The fuel pump should be fine since you tried two. 
The bowls fill up at idle.
It is not the secondaries because you disconnected them  - how did you disable the vacuum secondaries?

For me, this leaves:
the fuel pressure (delivery under load or after driving) (unlikely though because you probably can start your test from idle when the bowls are full),
fuel delivery due to something else with the high speed circuit of the carburetor on the primary side,
something with the ignition or gas as suggested by KD.

Swapping the carb is a possibility.

At this point, if it were me, I would probably go back and recheck everything  with the ignition.
Are there any other possible symptoms.   
Is the timing fine? 
What type of ignition do you have?

[johnnycharger]

Im flummoxed.

It sounds like you have some information.
Fuel level is OK. 
The squirt through the nozzles is fine - you see it come out as soon as you move the throttle and the pump shot lasts for about 0.5 to 1.5 seconds - correct? Yes
The fuel pump should be fine since you tried two. 
The bowls fill up at idle.
It is not the secondaries because you disconnected them  - how did you disable the vacuum secondaries? Removed the lever from the linkage on the driver's side.

For me, this leaves:
the fuel pressure (delivery under load or after driving) (unlikely though because you probably can start your test from idle when the bowls are full),
fuel delivery due to something else with the high speed circuit of the carburetor on the primary side, I don't know anything about the high speed circut
something with the ignition or gas as suggested by KD.

Swapping the carb is a possibility.

At this point, if it were me, I would probably go back and recheck everything  with the ignition.
Are there any other possible symptoms.    Idle seems higher than before.
Is the timing fine?  I haven't checked it because I can't see as to how it would change on its own
What type of ignition do you have? Mopar electronic, firecore wires, new ngk plugs

I answered above. I tried to change the font color but it didn't seem to work.

[XH29N0G]

It is not the secondaries because you disconnected them  - how did you disable the vacuum secondaries? Removed the lever from the linkage on the driver's side.

I may be wrong, but I think this works for a mechanical secondary, but the vacuum secondaries are controlled by the pot on the passenger side.  The driver's side just works to force the secondaries closed when the throttle is released.  My guess is still that the vacuum secondaries are not opening, but you would need to disable it some other way.  I do not know if it can be held shut with some sort of thing holding the rod connection the vacuum pot (diaphragm) to the secondaries, if those can be disconnected there, or if the diaphragm can be disabled by opening the top and putting in a much stronger spring.  

fuel delivery due to something else with the high speed circuit of the carburetor on the primary side, I don't know anything about the high speed circuit
The high speed circuit is the jets (the only thing I can think of is they are blocked) or something related to how air and gas makes it through the metering block (primary side) and metering plate (secondary side).  Some hole would be clogged.  This would require removing/disassembling, cleaning, and rebuilding the carburetor.  I wouldn't start with this step.  I would instead swap another carb in (like the one KD offered) first as a check.  It could be your carb is fine.

Are there any other possible symptoms.    Idle seems higher than before.
This could be the idle screw or mix on the carburetor or it could be something like the vacuum advance. Otherwise, I am not aware that a faster idle is an indication of a problem.  
Is the timing fine?  I haven't checked it because I can't see as to how it would change on its own  I don't think it would change on its own either,  Just asking in case it had been changed.  I was grasping at straws.
What type of ignition do you have? Mopar electronic, firecore wires, new ngk plugs


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[c00nhunterjoe]

Lots going on here. Couple quick tests.
-Secondaries disconnected
- verfy fuel pressure under full load
-Locked in a gear, bring rpm up to 3,000 rpm and then wide open- does it still stumble? If not, advance initial timing and retest.

[DanielRobert]

Holley carb? Did you try turning the adjuster spring nut and analyze if the shot is too much or not enough? Choke operating ok? Easy to overlook that part.

[johnnycharger]

It is not the secondaries because you disconnected them  - how did you disable the vacuum secondaries? Removed the lever from the linkage on the driver's side.

I may be wrong, but I think this works for a mechanical secondary, but the vacuum secondaries are controlled by the pot on the passenger side.  The driver's side just works to force the secondaries closed when the throttle is released.  My guess is still that the vacuum secondaries are not opening, but you would need to disable it some other way.  I do not know if it can be held shut with some sort of thing holding the rod connection the vacuum pot (diaphragm) to the secondaries, if those can be disconnected there, or if the diaphragm can be disabled by opening the top and putting in a much stronger spring.   GOOD POINT.

fuel delivery due to something else with the high speed circuit of the carburetor on the primary side, I don't know anything about the high speed circuit
The high speed circuit is the jets (the only thing I can think of is they are blocked) or something related to how air and gas makes it through the metering block (primary side) and metering plate (secondary side).  Some hole would be clogged.  This would require removing/disassembling, cleaning, and rebuilding the carburetor.  I wouldn't start with this step.  I would instead swap another carb in (like the one KD offered) first as a check.  It could be your carb is fine.I WAS TRYING TO AVOID IT BUT I AM THINKING THIS SWAP MAY NEED TO BE THE NEXT MOVE.

Are there any other possible symptoms.    Idle seems higher than before.
This could be the idle screw or mix on the carburetor or it could be something like the vacuum advance. Otherwise, I am not aware that a faster idle is an indication of a problem.  
Is the timing fine?  I haven't checked it because I can't see as to how it would change on its own  I don't think it would change on its own either,  Just asking in case it had been changed.  I was grasping at straws.
What type of ignition do you have? Mopar electronic, firecore wires, new ngk plugs


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[johnnycharger]

Lots going on here. Couple quick tests.
-Secondaries disconnected
- verfy fuel pressure under full load
-Locked in a gear, bring rpm up to 3,000 rpm and then wide open- does it still stumble? If not, advance initial timing and retest.

As in power braking? See if it roasts them or stumbles? Am I understanding correctly?
This sounds like the most fun test yet.

[johnnycharger]

Holley carb? Did you try turning the adjuster spring nut and analyze if the shot is too much or not enough? Choke operating ok? Easy to overlook that part.

Yes it is a Holley. I did adjust the accelerator spring nut.  Electric chock seems fine I didn't pay much attention to it to be honest.

[XH29N0G]

Verify, but I think C00nhunter means to cruise in gear (in 1st or 2nd) at 3000 and then floor it from the cruise.  This should have the mechanical advance largely in and the carburetor should have transitions to the high speed circuit (jets and boosters). I have not gone wrong when following his suggestions. 

[b5blue]

  By now I'd say pull the plugs and check condition/clean and check gap, check inside the Dist. cap for carbon tracking/cracks. While in there check rotor and that advance movement is smooth and springs back nicely. Undo and tighten ALL grounds. Battery and charging system condition? (Battery at full charge?) You have done enough farting around to possibly foul the plugs so get them to known readable condition. Have you checked the "quality" of the spark? 

[c00nhunterjoe]

Verify, but I think C00nhunter means to cruise in gear (in 1st or 2nd) at 3000 and then floor it from the cruise.  This should have the mechanical advance largely in and the carburetor should have transitions to the high speed circuit (jets and boosters). I have not gone wrong when following his suggestions. 

This

[johnnycharger]

Ok. When the rain stops I will try that.
Here is a link to what my new plugs look like.
https://youtu.be/eUEDfwLD8O0

[DanielRobert]

Maybe excessive blow by......change the plugs and see what happens. I would foul plugs really quickly with my pvc hooked up and too much idling with a lot of fuel/oil blow by never fully burning off the plugs. Falling flat and not recovering sounds like a stuck choke or running the bowl dry. Change carb after plugs.

[johnnycharger]

Verify, but I think C00nhunter means to cruise in gear (in 1st or 2nd) at 3000 and then floor it from the cruise.  This should have the mechanical advance largely in and the carburetor should have transitions to the high speed circuit (jets and boosters). I have not gone wrong when following his suggestions.  

This

Ok. I tried this and it stumbles and sputters. It seems like it has changed since I put in the new fuel pump. It still sputters and stumbles but not like it is going to shut off.
Here is the latest drive:
https://youtu.be/OIZE-qa47qg

[DanielRobert]

you sure the choke isnt stuck too far closed or the air cleaner isnt somehow pinching the choke butterfly rod? That would explain a higher idle since it would be running on the passenger side of the carb choke cam. Open the choke all the way and take off the air cleaner....then drive it to eliminate that part. It's running like a stuck choke(air) no fuel(dirt) or fouled plugs(even if new but fouled )  Also wondering at how strong of spark your getting at this point but need to eliminate the simple stuff.

[johnnycharger]

you sure the choke isnt stuck too far closed or the air cleaner isnt somehow pinching the choke butterfly rod? That would explain a higher idle since it would be running on the passenger side of the carb choke cam. Open the choke all the way and take off the air cleaner....then drive it to eliminate that part. It's running like a stuck choke(air) no fuel(dirt) or fouled plugs(even if new but fouled )  Also wondering at how strong of spark your getting at this point but need to eliminate the simple stuff.

Great idea. Thank you. I will try this tomorrow (weather permitting).

[Kern Dog]

I had the 850 Demon rebuilt by a guy here in town. I removed the choke years ago and tossed all the parts but wanted one again. He found the LAST electric choke kit in the country...In Utah!
The first several cold starts had the car running excessively rich until it was up to temp. Black smoke, air/fuel ratio in the 10s and below. I adjusted the choke housing to where the butterfly was about 1/3 open at rest and it starts and runs great again. I can't imagine an engine that would run right with so little airflow that a fully closed choke butterfly causes.

[johnnycharger]

SUCCESS!!!  Thank you all so much for helping me out with this. I feel so silly.
I took the air cleaner off and she runs like a champ!   While looking to try to determine what the air cleaner base was interfering with I noticed my carb seemed to be leaking gas into it for about 5 mins after I turned it off. Here is another video. The boiling sound is what got my attention.

https://youtu.be/qMJTlCVpqnc

[Kern Dog]

Wow...I hope that you found the problem!
I'd suggest to change the oil before running the engine. All that fuel went either into the exhaust or past the rings and into the oil.  It surely diluted the oil enough to warrant replacing.

[XH29N0G]

Have you traced where the fuel is coming from?  and why? 

[johnnycharger]

Wow...I hope that you found the problem!
I'd suggest to change the oil before running the engine. All that fuel went either into the exhaust or past the rings and into the oil.  It surely diluted the oil enough to warrant replacing.

I am thinking it went out the exhaust. The dipstick doesn't smell like gas?

Have you traced where the fuel is coming from?  and why? 

No, it only did that the one time. Kind of odd.

[c00nhunterjoe]

That is either fuel boiling up or a sticking needle and seat. But if it did that for 5 minutes, i would lean to fuel boiling. Time for a blocked egr pan and coolcarb spacer.

[DanielRobert]

I agree with the above assessments....gotta think about fuel pressure that could be building up too.

[johnnycharger]

That is either fuel boiling up or a sticking needle and seat. But if it did that for 5 minutes, i would lean to fuel boiling. Time for a blocked egr pan and coolcarb spacer.

Thank you. I used to have one of those fenolic(?) Spacers on it but my air cleaner keeps hitting my hood pad. Maybe that kept it cooler before?

[johnnycharger]

https://youtu.be/JdUWCZKMebM

After driving it again today I can see the gas is still running into the carb after it is off. I think this means it is the needle and seat.

[XH29N0G]

Fuel is coming out through the boosters.  

I believe needle and seat would be for the float and happen while there was fuel pressure (fuel pump on) and would stop when shut off.  Boiling would expand the fuel and push it through from inside and continue after shut off.  My guess is that the diagnosis will be related to expanding/boiling.

See what the others say.

How high is the fuel set in the bowls?

[c00nhunterjoe]

You can double check the float level while its idling, but if it runs to that extent for 5 minutes after the car is shut off, its boiling.

[johnnycharger]

I have ordered the Cool Carb spacer. I will provide an update once I receive it.