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440 six pack-hesitation/popping under hard acceleration

440-6pack

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Hi everyone,

I need your help!

I have a 1971 Challenger 440 6-pack, 4 speed. It was running great last fall. This spring when I took it out, it ran great the first week then slowly started hesitating on hard acceleration. Now when I stomp the gas from a rolling stop or downshift it sputters, pops and cuts in and out something fierce. However, it idle great when warm, revs up all day long in neutral and has lots of power if I accelerate slowly under load.

What I have done to date:

FUEL
  1. Changed fuel filter. I have an electric pump rated 5.5-9psi. I’m getting 5psi at the carbs. No return line.
  2. I’ve adjusted the floats to get a dribble from the port.
  3. I replaced the gas tank last year and have only run high octane (91-94)
  4. I installed a Holley refresh kit and 6.5 power valve, #31 squirter on main carb
  5. Installed the orange accelerator pump cam
  6. A/F adjustment screws at 2 turns for max vacuum 22inHg
VACUUM
1. Manifold reading at idle 24 inHg
2. Ported reading at idle 3 inHg
3. Ported reading 22-24 inHg but fluctuates +/- 2 inHg when I hold at 2500rpm
4. I tried a smoke test via the brake booster hose. Smoke just came out the top of the carbs...

TIMING
1. Base timing 15*@900 rpm, total mechanical advance at 3000rpm 38*, total with vacuum advance 55*

IGNITION
1. Mopar electronic ignition
2. New flame thrower coil. Tried my spare flame thrower and stock coil.
3. New Mopar spark plug wires
4. New champion cap, rotor and spark plugs gapped at .035
5. New distributor with reluctor set at .008 and .020 with full vacuum advance. I tried my spare (new) distributor. Neither had any play in the shaft.
6. New Mopar ignition box and voltage regulator. Also tried my new spare of both.
7. New NOS ignition switch and full reproduction wiring harness. I double checked all bulkhead connectors.
8. Tried 2 rebuilt alternators, both producing 13.5-14 volts
9. I’m not sure if related but the reproduction tachometer smoked and let go a couple weeks back. I installed a new aftermarket with factory wiring and no issues for 1 month.

ENGINE
1. C440 HP block, compression even at 155-160 psi in all cylinders. It appears there are “motor home” heads that only accept RV12YC plugs. Don’t think this is an issue as it ran fine last year...
2. No signs of burning oil but lots of dry carbon deposits in tail pipes and 4 of the eight spark plugs. cylinders 5,6,7,8 were fouled, 1,2,3,4 were lean.

If anyone has any insight on what the problem could be I would be forever grateful. The next things I will try are replacing the intake gaskets to eliminate any potential vacuum leak as-we’ll as disconnecting the secondary carbs in case they are malfunctioning.

Thanking you in advance!
 

rklein71

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Couple of easy checks.....ensure you have a really good ground from engine to body and ECU is grounded as well. 2) idle car in the dark and see if you have any spark plug wires that are arcing to the headers/manifolds 3)
 

440-6pack

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4F1CAFF7-766B-418F-8789-6B63038B73E8.jpeg
1F503219-E336-4C31-8CB1-1E4A3E04F67F.jpeg
Thanks for the quick response. I recently cleaned every ground and refastened them with dielectric grease. I even added a ground strap from engine to firewall and have a ground from battery post to body. I haven’t checked for arcing...what would cause that? Wires are brand new and I even put the old wires back on. Either way, easy verification. Thanks. Here are some photos of the spark plugs.
 

dadeo1852

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Well if those are your new plugs already fouled like that I'd say you got carb issues, possibly jet sizes too fat, needle not seating and are you confident you have your accelerator pump adjusted correctly, orange pump cam in #2 and lever not bottoming out?
 

Daves69

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Let's see, running good last fall. Park it for winter now the rear half of the engine carbon fouls. I'm thinking a float or needle / seat is allowing an overly rich condition. If you lift the rear carb after running do you see any signs of raw fuel in the manifold?
I believe it is common to see the plugs run rich toward the rear but definitely not to the extent in the picture (lol).

As far as the pump, is it squirting fuel in the center carb as soon as you pump it? My valve below the nozzle hangs on me sometimes after sitting around…….
upload_2018-8-9_9-42-53.png
 

440-6pack

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Well if those are your new plugs already fouled like that I'd say you got carb issues, possibly jet sizes too fat, needle not seating and are you confident you have your accelerator pump adjusted correctly, orange pump cam in #2 and lever not bottoming out?

Thanks for the advice. I put a .015 feeler gauge between the adjustment screw and lever with pump lever not depressed.

What size jets should be in the carb? Needles seem to be seating properly as car stalls with needles all the way in.

Yes, pump can is in #2 position.
 

440-6pack

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Let's see, running good last fall. Park it for winter now the rear half of the engine carbon fouls. I'm thinking a float or needle / seat is allowing an overly rich condition. If you lift the rear carb after running do you see any signs of raw fuel in the manifold?
I believe it is common to see the plugs run rich toward the rear but definitely not to the extent in the picture (lol).

As far as the pump, is it squirting fuel in the center carb as soon as you pump it? My valve below the nozzle hangs on me sometimes after sitting around…….
View attachment 51506

How can I check the floats, needle/seats? I’ll pull the rear carb and check for raw fuel. If there is fuel. How would I fix the needles/seats/floats?

Squirter was just replaced and skirts nicely as soon as throttle is depressed.

Thank you
 

dadeo1852

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Jet size should be around 63 in center carb. I'm running 65 & absolutely no plug issues. I take it your choke works good and unloads quickly and your power valve is not blown. Look down the carbs with the engine idling, should not see gas dribbling, right.
As far as accelerator pump screw/lever - should be no gap when not depressed. Feeler gauge is for fully depressed.
Watch this.
 

440-6pack

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Jet size should be around 63 in center carb. I'm running 65 & absolutely no plug issues. I take it your choke works good and unloads quickly and your power valve is not blown. Look down the carbs with the engine idling, should not see gas dribbling, right.
As far as accelerator pump screw/lever - should be no gap when not depressed. Feeler gauge is for fully depressed.
Watch this.



It is a brand new Holley power valve (6.5). There is no choke. I’ll check for gas dribbling. Thanks for the video, I will readjust. Although this should hopefully address the fouling issues. Any ideas why the car is cutting in and out on hard acceleration?
 

dadeo1852

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You know it's so hard to diagnose without being there but you say it's fine accelerating slowly meaning you do or do not slowly put it to the floor. If you do put it to the floor slowly and it acts fine and only does it when you stomp on that pedal, my opinion would be starving for fuel & getting a lean pop but once main circuit comes in it should just accelerate assuming fresh plugs.
Man I keep going back to the accelerator pump, possibly diaphram bad, hard or ripped but you say with engine off giving it throttle it squirts good from the nozzle? By the way mine hesitated until I put a pink cam in #2.
Are you running performance cam?
Did you run it with the new and old tach disconnected?
 

Daves69

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It was running great last fall.

This is the statement that suggests something has changed while just sitting in the garage.
IMO, Over time the plastic floats can loose buoyancy and the tin floats can leak. Inadequate pressure from the float can allow the pump pressure to overwhelm the needle and seat and cause a flooding condition. Being the rear four plugs fouling, I'm looking at the rear and center carb for issues.
The junk they sell which they call "gas" these days don't help the seat seals either or corrosion possibilities. I make it a point to use Stabil in all my gas except for my daily driver around here. The water just drips from the exhaust.
Curious, do you run the inlet filters on your carbs?

On a side note, I have a 2300 on my Glastron I/O. Bought it new in 2008. All the 87 octane gas I ever put in it has had Stabil added to it. Over winter I fill the tank and add Stabil. It sits for 5-6 months over winter until fired up in the spring.
In 2016 I decided it was time to clean the muck and any corrosion out of the carb it might have accumulated.
Here is what the teardown revealed. What do you think?..….
BoatCarb1.jpg
BoatCarb2.jpg
 

wedg2go

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My thoughts are the same as Dave's (something is not right with the rear outboard or center 2300). He also brought up another point...quality of gas. Water in the tank?

However, if you haven't done so, take a few minutes and check the distributor reluctor once more and see if "each" point is .008.
 

dadeo1852

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Well I hear you guys. That's why I asked if it's dribbling.
By the way, that's the cleanest fuel bowl & metering plate I've ever seen!
 

440-6pack

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Hi again,

The main carb has a Holley refresh kit that I just installed a week ago. Included all new gaskets, float needle, power valve and accelerator pump diaphragm.

The engine has a stock cam. I’ll try the pink cam. I’ve tried it with new tach connected and disconnected. No difference.

I don’t have any carb inlet filters. Only the main filter at the tank. I’ve only run between 91-94 octane.

I’ll check the gap for all reluctor points and take apart the rear outboard.

That is a clean carb Dave!
 
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rklein71

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It is interesting that the back cylinders are fouling and front seem to be okay, or at least a lot better.....seems to indicate a rear carb issue. I had to rebuild my six pack with ethanol friendly rebuild kits. They include needle and seats that can handle the alcohol.
 

440-6pack

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Update:
  1. I disconnected secondaries and plugged the port on main carb, no change.
  2. There are no dribbles of fuel out of the nozzle at idle.
  3. I put my hand over the top of the carb and it died instantly, meaning there should be no vacuum leak. I bought new gaskets anyway, just haven't had the time to change them.
  4. I adjusted the accelerator pump so that there was .015 with throttle fully depressed.
No change with the above trials. However, some new information. I forgot to mention that I installed a new reproduction exhaust system and original exhaust manifolds that were blasted and painted this spring before taking the car out. I didn't think this would be the cause as everything was new...

The sound I hear when I stomp on the gas is like a "big puff" of air when the car cuts out.
Also, I noticed that there is an irregular light puffing sound coming out the exhaust at idle, and the idle is a little rough. I also noticed at cruising speed, there are some tinny misfires that just vibrate the shifter every now and then. I did some "googling" and some would think this is a bad exhaust valve(s) or bent/broken push rod(s)...

I still have to check all the reluctor point gaps and arcing/cross-firing at night.

Any new thoughts would be appreciated.

Thanks
 

DetMatt1

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Hi again,

The main carb has a Holley refresh kit that I just installed a week ago. Included all new gaskets, float needle, power valve and accelerator pump diaphragm.

The engine has a stock cam. I’ll try the pink cam. I’ve tried it with new tach connected and disconnected. No difference.

I don’t have any carb inlet filters. Only the main filter at the tank. I’ve only run between 91-94 octane.

I’ll check the gap for all reluctor points and take apart the rear outboard.

That is a clean carb Dave!
It doesn’t matter what octane the fuel is if it still has the ethanol. I run marine 2 cycle engine oil in my gas, at least 1 oz per every 5 gallons of gas. If you’ve never treated your gas for the ethanol I suggest you start and I would also clean out your carbs of the gelatinous slime that might have accumulated in the bowls. The ethanol will also deteriorate rubber fuel lines to the point you could start to suck air into the system right through the hose and not have any fuel leaking out.
 

440-6pack

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Thanks Det-Matt1,

I will begin the recommended treatment. This is the first I hear of the 2-stroke oil. Very interesting. As mentioned in a previous post. I just cleaned the carb and installed a Holley refresh kit. The carb was very clean when I opened it, no deposits or slime.

Thanks
 

dadeo1852

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Just going through process of elimination, so, are you absolutely certain when you reinstalled the spark plug wires you have the firing order right, 18436572 counter-clockwise, double check, even maybe replace with old set just to take this off the list of potential problems.
 
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