Rough Idle (Missing) Under Load

[glrestomod]

Hello! I searched the forum but can’t find anything similar to what the problem I’m having with my 1969 Dodge Charger 383-4bbl Holley 4160 600 cfm (not a double pumper). The engine is a 1970 383 and I just had the carburetor rebuilt, added a new fuel filter, a new alternator and voltage regulator (on the firewall), as well as new plugs and wires. It has the black box electronic ignition from Mopar Performance (put on the car in around 1998). The engine was rebuilt in about 2003 but has less than 5000 miles on the rebuild. Bored 0.60 over but built as a cruiser with a stock camshaft, etc. Not sure the exact specs in the cam.

Having said all of that, the car idles rough and misses when in drive or reverse. In park or when driving at speed it’s smooth as silk. Idles great in park. It gets so rough it will die if I don’t give it the gas. Any idea what I may be dealing with? It did this before I replaced all of those things above and still does it after all of those things have been replaced as well. Any suggestions and advice are greatly appreciated!

 

[Geoff 2]

Sounds like a problem in the idle cct....or an air leak. Do the idle mixture screws make a difference to the idle quality/speed?

 

[lewtot184]

Look at the front of the choke tower for a "list" number. Tell us what that number is and maybe we can find more info on the carb.

 

[glrestomod]

Sounds like a problem in the idle cct....or an air leak. Do the idle mixture screws make a difference to the idle quality/speed?

It doesn’t as far as it eliminating this under load idle issue unfortunately

 

[glrestomod]

Look at the front of the choke tower for a "list" number. Tell us what that number is and maybe we can find more info on the carb.

Thank you! I don’t see any numbers in that location. There is a 11761 on the top of the carb. And the part number is 0-80457S if that helps.

 

[turbine68rt]

When did you replace the distributor, and is it a proform or oem chrysler style?

 

[glrestomod]

Look at the front of the choke tower for a "list" number. Tell us what that number is and maybe we can find more info on the carb.

Thank you! I don’t see any numbers in that location. There is a 11761 on the top of the carb. And the part number is

When did you replace the distributor, and is it a proform or oem chrysler style?

it’s been a while, like 1998 or 1999 on the distributor. It was in an electronic ignition set from Mopar Performance with the black box

 

[Carcinogen]

In park or neutral Does engine rev OK?

When engine is under load the cylinder pressure needs stronger spark. recommend checking ignition coil, voltage to coil, ignition wire resistance, and proper ignition advance in distributor.

On my 72 Plymouth I found problems with the old stock wiring that dropped voltage to coil and also affected the charging system. (Lights would cycle dim then back to normal). wire coating looked ok but under insulation the wire was discolored with green spots of corrosion. Connectors were also old and showing corrosion, running new wire solved engine stumbling under load and dimming lights problem.

 

[turbine68rt]

Thank you! I don’t see any numbers in that location. There is a 11761 on the top of the carb. And the part number is

it’s been a while, like 1998 or 1999 on the distributor. It was in an electronic ignition set from Mopar Performance with the black box

Just to eliminate a possiblity, take out your distributor and while rotating the shaft maually, check the reluctor gap at each point to verify you have a consistent gap, I think it's .008" using a brass feeler. I have seen a replacement distributor have a certain amount of eccentricity, causing a stall-under-load condition. The proper gap was set at the closest point and cured the stalling issue. This was on my brother's Coronet with a Proform unit.

 

[lewtot184]

Thank you! I don’t see any numbers in that location. There is a 11761 on the top of the carb. And the part number is 0-80457S if that helps.

Ok. I messed with an early 80457 (has the adjustable floats, later versions don't) and I noticed the carb was calibrated a little lean out of the box. I think looking carefully at the idle to make sure it's not too lean and going up one or two jet sizes on the primary side may help.

 

[Daves69]

as well as new plugs and wires.

You might check your firing order and verify the wires are correct. Especially the 5 & 7.

 

[Don Frelier]

Grab some rubber gloves and pull a plug wire at a time and see if any particular plug or plugs don't change the idle speed or quality. If one or 2 have no effect then you need to investigate further on those cylinders. Try a different plug, compression check etc...


If it changes drops speed when any of the 8 plugs are disconnected then it's likely a mixture or timing issue.

 

[glrestomod]

Look at the front of the choke tower for a "list" number. Tell us what that number is and maybe we can find more info on the carb.

Thank you! I don’t see any numbers in that location. There is a 11761 on the top of the carb. And the part number is

Sounds like a problem in the idle cct....or an air leak. Do the idle mixture screws make a difference to the idle quality/speed?

Sounds like a problem in the idle cct....or an air leak. Do the idle mixture screws make a difference to the idle quality/speed?

so I attempted a second time to adjust the idle screws. It runs rough even when adjusted to run the least rough. Where it’s at currently is the where it isn’t as bad. Gonna try a timing light soon.

 

[glrestomod]

Grab some rubber gloves and pull a plug wire at a time and see if any particular plug or plugs don't change the idle speed or quality. If one or 2 have no effect then you need to investigate further on those cylinders. Try a different plug, compression check etc...


If it changes drops speed when any of the 8 plugs are disconnected then it's likely a mixture or timing issue.

Thank you! I checked all my plugs, none are fouled. Gonna get a timing light and check that. The mixture screws are best where it’s currently set, but still is rough. Gonna try to adjust the idle screws with a vacuum gauge afterwhile when my neighbor gets home to help me. Thanks for the help!

 

[glrestomod]

Look at the front of the choke tower for a "list" number. Tell us what that number is and maybe we can find more info on the carb.

Thank you! I don’t see any numbers in that location. There is a 11761 on the top of the carb. And the part number is

In park or neutral Does engine rev OK?

When engine is under load the cylinder pressure needs stronger spark. recommend checking ignition coil, voltage to coil, ignition wire resistance, and proper ignition advance in distributor.

On my 72 Plymouth I found problems with the old stock wiring that dropped voltage to coil and also affected the charging system. (Lights would cycle dim then back to normal). wire coating looked ok but under insulation the wire was discolored with green spots of corrosion. Connectors were also old and showing corrosion, running new wire solved engine stumbling under load and dimming lights problem.

I’m hoping mine isn’t the wiring harness but that’s a strong possibility, as I put a new coil on it last night and still have the same issue. My lights actually seem fine believe it or not, besides a bad ground that has the passenger side hood mounted turn signal stay on when the lights are on.

 

[68-500]

Vacuum leak?

 

[glrestomod]

Vacuum leak?

My neighbor and I checked for one before and we didn’t have one. However, the carb was rebuilt and reinstalled so we’ll try to check it again tonight or tomorrow! Thank you!

 

[Don Frelier]

Thank you! I checked all my plugs, none are fouled. Gonna get a timing light and check that. The mixture screws are best where it’s currently set, but still is rough. Gonna try to adjust the idle screws with a vacuum gauge afterwhile when my neighbor gets home to help me. Thanks for the help!

There's a difference between pulling the plugs and looking at them as opposed to what I described removing each plug wire while it's running.
Did you try this?

 

[glrestomod]

There's a difference between pulling the plugs and looking at them as opposed to what I described removing each plug wire while it's running.
Did you try this?

I agree, I was just letting you know what I’ve tried thus far. I haven’t yet, hoping to be able to tomorrow! Thanks again!

 

[glrestomod]

I agree, I was just letting you know what I’ve tried thus far. I haven’t yet, hoping to be able to tomorrow! Thanks again!

Sorry for the long delay! Had a lot going on! So I did what you recommended and one of the brand new, universal fit, plug wires was bad! I have a new set that will be delivered on Black Friday. The ones on it are a generic universal fit from O’Reiley’s. I have a set of Taylor 8MM wires that say they work well with electronic ignition and are made just for my Mopar big block.