Slight acceleration hesitation driving me mad

[Coronet-383]

hey everyone, so me and my dad spent all day making adjustments and I still have a slight hesitation when accelerating from a dead stop. I have a 69 dodge Coronet 500 with a 383 4brl. To my knowledge everything is all original including the Holley 4160. I was having a issue with the car stalling out when coming to a stop and ended up rebuilding the Carburator. Everything is great when I’m on the road cruising, I can go 55 and put the pedal to the floor and she continually pulls. We seem to have the timing right now it’s set at about 7.5 btdc and has more power than ever. We hooked up a vacuum gauge to it and set the mixture screws properly, idle speed is set correctly, made the .015 measurement at the accelerator pump at wot, have the accelerator cam in the #1 positions, the only thing left I can think of is the accelerator pump shooter needs to go up a couple sizes, but would I need to do this for a completely original configuration? Everything we have done so far has helped and is getting better, just can’t seem to get rid of the hesitation. Any help is appreciated thank you!

 

[bolson6333]

I'm guessing you have ruled out the distributor gap and mechanical advance.

 

[Lefty71]

Agree. Be wary of a worn distributor, or its internals. If all ignition is good, I'd say looking to the pump shooter is the right direction.

 

[Coronet-383]

I'm guessing you have ruled out the distributor gap and mechanical advance.

I haven’t double checked the points gap, but just replaced cap, rotor, points and condenser last year, and new plugs and wires two weeks ago.

 

[Coronet-383]

Agree. Be wary of a worn distributor, or its internals. If all ignition is good, I'd say looking to the pump shooter is the right direction.

By internals are you referring to points and condenser rotor etc? I’m not sure what else is in a disributor, I’m still kinda learning all this as I go.

 

[Lefty71]

You may need a dwell meter, and you may need to look closely at the the cam that actuates the points for wear or damage. Is this a single points set-up? If everything looks very good with the points, then move on to timing. Have someone else start the car whilst watching the timing with the light, and then rev the car somewhat while watching. Are the timing events happening smoothly, or is the light jumpy?? If all looks good, then I'd move on to look more closely at the carb, but if not, you may want to consider a different distributor, or a known good one for testing, preferrably a dual point. HTH, Lefty71

 

[Bill76]

I would bump up the timing a tad and see if anything changes

 

[Don Frelier]

Try 12 degrees of advance

 

[Coronet-383]

You may need a dwell meter, and you may need to look closely at the the cam that actuates the points for wear or damage. Is this a single points set-up? If everything looks very good with the points, then move on to timing. Have someone else start the car whilst watching the timing with the light, and then rev the car somewhat while watching. Are the timing events happening smoothly, or is the light jumpy?? If all looks good, then I'd move on to look more closely at the carb, but if not, you may want to consider a different distributor, or a known good one for testing, preferrably a dual point. HTH, Lefty71

Yes it’s single points set up. I replaced the points and condenser last summer, and regapped it then, I haven’t double checked the gap yet. But watched the timing line advance smoothly while rpms went up under timing light. It feels like something along the accelerator pump maybe because once it is on the road at 55mpg I floor it and it just pulls and goes faster, it’s only from a dead stop that it hesitates. Everything I read and seen in videos from Holley it seems like I may need bigger size accelerator shooters, but everything is all original on the car so I wonder why it might need that or if it is even the issue.

 

[Coronet-383]

Try 12 degrees of advance

I tried around 10-11 degrees because I read that in other threads and was sluggish compared to 7.5 btdc, so I set it back to the service manual specs

 

[Coronet-383]

I would bump up the timing a tad and see if anything changes

We messed with timing all day it seems best and most powerful at 7.5 btdc

 

[Jerry Hall]

Could be a weak advance spring. To much advance to to quick.

 

[miller]

I tried around 10-11 degrees because I read that in other threads and was sluggish compared to 7.5 btdc, so I set it back to the service manual specs

Something you should understand...especially with today's crap gas.

In your distributor, the mechanical advance 'degrees', or how much advance, is set. Mopar engines only want 34-35 MAX, when fully advanced. However much advance is in the distributor, it 'follows' whatever initial your timing is set.
Meaning, if the distributor was set-up for 7.5 initial, it probably has 26.5 degrees advance in it, to reach 34-35.
Trying the initial at 10, no change on the advance, goes to around 36.5 full advance.

Anyway, just giving you some basics, on the mess. Changes would need to be made in the distributor, to make it work.

 

[ddpsnake]

What color pump cam in that holley also try the #33 discharge nozzles.I always have to play with the pump cam buy a kit there's like 8 or so .

 

[Coronet-383]

What color pump cam in that holley also try the #33 discharge nozzles.I always have to play with the pump cam buy a kit there's like 8 or so .

It’s a creamish pinkish white color cam haha, I’m assuming it’s been on the car since it was new. Theoretically if everything is all Original the #31 discharge nozzles in it should still be perfect for the set up shouldn’t they? What might be a reason they no longer are adequate and require upgrade? besides the obvious hesitation, cuz the car run so beautiful at cruising speeds.

 

[Coronet-383]

Something you should understand...especially with today's crap gas.

In your distributor, the mechanical advance 'degrees', or how much advance, is set. Mopar engines only want 34-35 MAX, when fully advanced. However much advance is in the distributor, it 'follows' whatever initial your timing is set.
Meaning, if the distributor was set-up for 7.5 initial, it probably has 26.5 degrees advance in it, to reach 34-35.
Trying the initial at 10, no change on the advance, goes to around 36.5 full advance.

Anyway, just giving you some basics, on the mess. Changes would need to be made in the distributor, to make it work.

So I can change the timing in the distributor and should change that to 10 degrees instead of using the timing light to advance it to ten degrees at the timing mark on front of the engine? Am I understanding that correctly?

 

[Cranky]

Advancing the timing that little bit made it sluggish? Wow. Don't recall ever having a car get sluggish with timing around 12 degrees. First thing I would do it check to make sure your balancer ring hasn't slipped. How many miles on the ignition parts in the dizzy and what brand are they. The only brand I would run were Blue Streak/Standard. They stayed good while everything else turned to junk. Keep in mind that when the dwell changes, so does the timing but changing the timing doesn't affect the dwell so set the dwell first.....and for each degree of dwell increase, the spark is retarded by one degree at the crank and that's why you set the dwell first.

 

[RJRENTON]

Coronet383,
I believe in 1969, Mopar introduced the Holley 4160 carb on the 383 engine. Being a side hung float carb, it is sensitive to primary fuel level.
In addition, I believe that model carb used a "back-ward" idle fuel system in that the user adjustable "mixture screws" are adjustable AIR bleeds....screwing them IN, richens the mixture by reducing air flow in the idle and off idle transition circuit. There is a fixed idle fuel orifice in the primary metering block that determines fuel flow to the adjustable idle air bleed circuit, which determines just how much fuel can be introduced. This was an emission control attempt to reduce hydrocarbon and carbon monoxide emissions.
The fix? Run the primary fuel level slightly higher to provide more fuel, so the idle circuit has an adequate volume. In the primary metering block, locate the idle fuel feed circuit and drill the restriction approx. 0.001" larger, using a pin vice and number drills, by hand. As an alternate, REDUCE the size of the idle air bleeds in the air horn, but it's easier to redrill the fuel feed origices. GO SLOW SMALL CHANGES WILL MAKE A HUGE DIFFERENCE IN THE FUEL DELI VERY. Mopars seem to like a slightly rich idle and off idle to eliminate a stumble condition.
The Holley is a great carb in spite of what you have heard or have been told including the "Eddy" boys. The primary metering block has all of the fuel emulsion circuits for both the idle and off idle transition circuit and primary fuel systems.
Just my opinion of course.
Bob Renton

 

[Cranky]

So why would a Mopar like a slightly rich idle and off idle to eliminate a stumble condition? That carb doesn't know or care what brand of ICE it's on......

 

[RJRENTON]

So why would a Mopar like a slightly rich idle and off idle to eliminate a stumble condition? That carb doesn't know or care what brand of ICE it's on......

I do not know what your reference to ICE neans.
Fuel distribution (density of mixture) and mixture velocity have everything to do the engine's response characteristics ALONG WITH other variables such as ignition timing, cam overlap and probably the biggest issue is the percentage of ethanol in the fuel being consumed. As I've noted in previous correspondence on the forum, ethanol blended fuels have lower heating (energy) values and the consumed volume of fuel should be increased (slightly richer) to provide the equivalent energy to achieve the same results...smooth, powerful, without hesitation or stumble operation.
Bob Renton