Anyone else have minor hesitation/jerking at part throttle??

NWPT70

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Ok to summarize, I know my initial timing is at 10°BTDC and my vacuum advance works. Just took the car out for a nice long run with the newly installed Champion spark plugs and a full tank of 93 octane gas with Ethanol stabilizer added. Really runs like a top overall but unfortunetly still has the partial throttle "fish nibbling" feeling going on at light throttle under load. I've noticed it will do this even at low speeds (10-15mph) as well as highway light throttle cruising (45-50). But at any given time, increasing the throttle a notch makes it go away.

Id like to confidently turn down the path of looking into a possible fuel system issue. It really seems like an issue with the transition circuit of the carburetor. (The 2 barrel BBD was rebuilt last fall by a reputable rebuilder in my area.) Fuel filter was replaced also at that time.

Has anyone had experience upjetting these carbs by one size larger then factory? How about different size metering rods?

By the way I noticed a metal electrical Male spade connector on the carb near the throttle linkage that is not connected to anything. What is this for?
 

Ripinator

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Ok to summarize, I know my initial timing is at 10°BTDC and my vacuum advance works. Just took the car out for a nice long run with the newly installed Champion spark plugs and a full tank of 93 octane gas with Ethanol stabilizer added. Really runs like a top overall but unfortunetly still has the partial throttle "fish nibbling" feeling going on at light throttle under load. I've noticed it will do this even at low speeds (10-15mph) as well as highway light throttle cruising (45-50). But at any given time, increasing the throttle a notch makes it go away.

Id like to confidently turn down the path of looking into a possible fuel system issue. It really seems like an issue with the transition circuit of the carburetor. (The 2 barrel BBD was rebuilt last fall by a reputable rebuilder in my area.) Fuel filter was replaced also at that time.

Has anyone had experience upjetting these carbs by one size larger then factory? How about different size metering rods?

By the way I noticed a metal electrical Male spade connector on the carb near the throttle linkage that is not connected to anything. What is this for?

If you were running points, I would suggest replacing the points and condenser, but you are running electronic ignition. BTAIM, I'm still thinking there is something not right in your ignition system.
 

Big_John

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Ok to summarize, I know my initial timing is at 10°BTDC and my vacuum advance works. Just took the car out for a nice long run with the newly installed Champion spark plugs and a full tank of 93 octane gas with Ethanol stabilizer added. Really runs like a top overall but unfortunetly still has the partial throttle "fish nibbling" feeling going on at light throttle under load. I've noticed it will do this even at low speeds (10-15mph) as well as highway light throttle cruising (45-50). But at any given time, increasing the throttle a notch makes it go away.

Id like to confidently turn down the path of looking into a possible fuel system issue. It really seems like an issue with the transition circuit of the carburetor. (The 2 barrel BBD was rebuilt last fall by a reputable rebuilder in my area.) Fuel filter was replaced also at that time.

Has anyone had experience upjetting these carbs by one size larger then factory? How about different size metering rods?

By the way I noticed a metal electrical Male spade connector on the carb near the throttle linkage that is not connected to anything. What is this for?
I was quick to jump on the "it's carb" bandwagon, but seeing the plugs and the color, I'm hesitant to say that's it.

Since the PO did the trick of the week spark plugs, I'd be tempted to go through some other things. Any idea of the age of the plug wires and other ignition pieces?
 

70bigblockdodge

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Did you try disconnected vacuum advance after plug change? I'm back to the canister adding too much advance at light throttle, because I agree with Big John on the color of the plugs looks good, not lean.
 

NWPT70

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I was quick to jump on the "it's carb" bandwagon, but seeing the plugs and the color, I'm hesitant to say that's it.

Since the PO did the trick of the week spark plugs, I'd be tempted to go through some other things. Any idea of the age of the plug wires and other ignition pieces?

The orange box Mopar electronic ignition kit was installed about 7 years ago and have about 1000 miles on them. The wires were installed at the same time and are thick Taylor 8 mm wires.

Jumping back on the ignition wagon.. I have been recommended earlier in the thread to try advancing the ignition by +2 degrees. I currently am at 10 degrees initial timing. What degree are these cars supposed to be set at? The under hood label says 2.5 degrees BTC but that seems way to low or maybe I am reading that wrong?. @Big_John @Ripinator

I also have been warned some of the orange ignition boxes had dead spots. I may pick up another box to swap in another box to see if things change.
 

NWPT70

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Did you try disconnected vacuum advance after plug change? I'm back to the canister adding too much advance at light throttle, because I agree with Big John on the color of the plugs looks good, not lean.

I haven't yet but will try that tonight.
 

Big_John

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The orange box Mopar electronic ignition kit was installed about 7 years ago and have about 1000 miles on them. The wires were installed at the same time and are thick Taylor 8 mm wires.

Jumping back on the ignition wagon.. I have been recommended earlier in the thread to try advancing the ignition by +2 degrees. I currently am at 10 degrees initial timing. What degree are these cars supposed to be set at? The under hood label says 2.5 degrees BTC but that seems way to low or maybe I am reading that wrong?. @Big_John @Ripinator

I also have been warned some of the orange ignition boxes had dead spots. I may pick up another box to swap in another box to see if things change.
I'd set it at factory spec and see what happens.
 

opus65

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The Holley two barrel was well known to warp due to the air cleaner bolt only engaging the top o the carb and not the throttle body. Mopar actually issued to Dealerships a "Bridge Kit" that added down pressure on the casting. My 71 Gran Coupe had the dreaded lean surge until I came across this fix. I may still have one somewhere. The local dealership had two left years ago and I bought both.
 

Yellow Galleon

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Hi all! New to the site. Figured I'd describe my experience with this. I have no vacuum advance. When I was getting my Polara back to running condition last year, I noticed I had a vacuum leak through the advance diaphragm. But for the life o' me, couldn't find the right part anywhere else. They are all BACKWARDS to how it's supposed to be installed on my distributor, so I capped off the line. I was not able to set initial timing to the factory specs without it running rough, so I just went by my vacuum gauge to run smooth at the lowest possible idle speed and then went from there's. It has ran beautifully in the bitter cold winter months, but noticed, as of late, a surge in acceleration from a standstill and after making a turn. Today, it has warmed up a bit close to 70 F and was a bit Gusty. It was misbehaving more than it's ever been on the way to work. The engine sounded like it wasn't entirely on cadence and surged once, like a misfire. However, on the way home from work, with winds calm and temps down to about 40 F, it was purring like a cat with power mostly restored during acceleration. Yesterday I went from 87 to 89 octane to see if that would make a difference but these shenanigans happened today. I have a 383, 727 trans, running accel ign components with ballast resistor mounted to the coil. It's got a 4 barrell carter AFB with manual choke. For most of it's driving life I ran 87 octane without much issue other than slight ping on acceleration. I suspect bad plugs, but it runs great at night.. like it hates hot weather anything warmer than 60. Welp, there's my experience.

IMG_20210205_110117.jpg
 
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CBODY67

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Are you buying gas at a higher-volume station? Might be some older gas in the tanks that is not formulated for the more variable temps we tend to have this part of the year?

Possibilities?
CBODY67
 

Slap Stick

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The Holley two barrel was well known to warp due to the air cleaner bolt only engaging the top o the carb and not the throttle body. Mopar actually issued to Dealerships a "Bridge Kit" that added down pressure on the casting. My 71 Gran Coupe had the dreaded lean surge until I came across this fix. I may still have one somewhere. The local dealership had two left years ago and I bought both.
In post #1 he states it has a Carter.
 

halifaxhops

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I have the right vacuum advances if needed. Just need info and which arm?
 

Yellow Galleon

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Original on left. Looking down on top of the open end, the tang is facing same direction as the nub on the arm. Incorrect on the right. Nub is facing opposite. Seems like everyone and their uncle Wallace has the one on the right.

IMG_20200904_215202.jpg
 

Yellow Galleon

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Are you buying gas at a higher-volume station? Might be some older gas in the tanks that is not formulated for the more variable temps we tend to have this part of the year?

I don't know for sure. I'm leaning towards a misfire from a spark plug.

Possibilities?
CBODY67
 

halifaxhops

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Right one is a SB/Slant do you know which arm it is take a pic of it if you can and also if there is a number there also.
Vacuum advance big block.jpg
 

Slap Stick

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Okay, let's think outside the box.

Is there slop in the timing sprocket/chain?
Is the oil pump/dizzy drive gear/ bushing worn?
Dizzy bushings?
All can affect valve and ignition timing. Under light throttle is when it will show up.
Axe me how I found out.
 

CBODY67

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My "outside the box" experiences with similar and a check engine light turned out to be one of the three ignition coils on my Chevy V-6. Having OBDII to identify that all of the misfires were happening on ONE cyl, consistently, helped. Replaced that one coil, all was well until it started happening again, so the other two coils were replaced, which fixed it again.

Just my experiences,
CBODY67
 

halifaxhops

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I still need the number on the arm should be on the Up side of it to get it right. You dont want to create more issues. Think I only have rebuilds of that style left. On the one on the left, just a picture of a LA one.

580065200-jpg.jpg
 
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