Carburetor stumble

[Some Car Guy]

He is not getting a lean stumble on transition. He states in the first post that when he is cruising & he stabs the throttle, he gets the stumble.

With main jets reduced by 3 sizes, it is going to need a sizable increases in the PVCRs to make up the difference & avoid a stumble.

That’s exactly what a transition is. He is moving the throttle a lot. It helps to understand basic carb function. When you open the blades suddenly, the engine takes in a big gulp of air. It needs the pump shot to make up for that and not go lean. It needs time to recover and draw enough fuel to match the air coming in. That’s what the accelerator pump makes up for.

 

[Geoff 2]

Sigh........
When he is cruising he is out of transition, past it.
Since the engine doesn't recover after falling flat on it's face, it tells you there is nothing there after the pump shot gets used up.

 

[Some Car Guy]

Sigh, you don’t seem to understand carb function. Two threads now. Until he tunes the accelerator pump, that is the place to look. This is the second time in two threads you’ve given off base info for a simple carb tuning issue. Clouding the matter with data dumps and theories when we are talking about everyday bread and butter issues doesn’t help anyone. A lean stumble in a throttle change calls for more gas. If he still has a lean out condition after addressing the initial need for more fuel, then we can talk about the power valve.

 

[Aron Gleason]

Sigh, you don’t seem to understand carb function. Two threads now. Until he tunes the accelerator pump, that is the place to look. This is the second time in two threads you’ve given off base info for a simple carb tuning issue. Clouding the matter with data dumps and theories when we are talking about everyday bread and butter issues doesn’t help anyone. A lean stumble in a throttle change calls for more gas. If he still has a lean out condition after addressing the initial need for more fuel, then we can talk about the power valve.

I will be taking the car out maybe tomorrow or Sunday to see if putting the blue cam in made a difference. So I'll update further.

 

[Some Car Guy]

If you can get an assortment that would be good. I like to have plenty of parts on hand when I do a drivability tune up. I go from parking lot to parking lot and tinker until I rod the best combo.

Holley has a bigger accelerator pump available. Has more cc in it. I don’t know what size the other brands run or of they can fit a Holley one. You might not need such a piece, but I did want to mention it.

 

[Aron Gleason]

I've got all 8 pump cams. The carburetor originally came with a pink cam, and I put a orange cam in. But after putting the blue cam in, I see how much I had to readjust the pump arm. So I'm crossing my fingers and toes for some good results.

 

[RemCharger]

Your secondary idle adjustment should be easily accessible. Give that a half crank to bring your primary to a lower value ,making it more inline with the proper transition slot.

 

[68 HEMI GTS]

After reading up on forums in regards to accelerator pump cams, people say with a stumble like I have. A more aggressive cam such as the blue cam has solved the issue. Knock on wood that gets me in the right direction.

Blue 427 cam is the most aggressive with a 30cc pump. They work well. When you adjust the arms you take all the play out correct?

 

[Aron Gleason]

Blue 427 cam is the most aggressive with a 30cc pump. They work well. When you adjust the arms you take all the play out correct?

Yes that's true. But I have it adjusted to where I had a little play in the arm. And extended the arm just enough to wheres there's no play so as soon as I move the throttle...the arm moves.

 

[68 HEMI GTS]

Yes that's true. But I have it adjusted to where I had a little play in the arm. And extended the arm just enough to wheres there's no play so as soon as I move the throttle...the arm moves.

Arm should have zero play. The clearence holley recommends is at WOT so the pump isn’t bottomed out.

 

[Aron Gleason]

Arm should have zero play. The clearence holley recommends is at WOT so the pump isn’t bottomed out.

Thats how I have it set to

 

[Aron Gleason]

Hopefully I'll have some good results after putting the blue cam in.

 

[52 Bone Speed]

Just letting you know I'm with ya on this journey. This is my first post, but I just a full rebuild on my 440 (and couple hundred hours redoing a crappy previous restoration). I do have an AFR and the meter. Motor is running awesome except for stab it or try to accelerate from idle or cruise and it falls flat with AFR going full lean. I do have a Torker II intake, 9.5:1 compression not too crazy of a cam. About to go through pump shot jets and cams and maybe a four hole spacer. Keep us posted on what worked and didn't in your journey to throttle response.

 

[Aron Gleason]

Just letting you know I'm with ya on this journey. This is my first post, but I just a full rebuild on my 440 (and couple hundred hours redoing a crappy previous restoration). I do have an AFR and the meter. Motor is running awesome except for stab it or try to accelerate from idle or cruise and it falls flat with AFR going full lean. I do have a Torker II intake, 9.5:1 compression not too crazy of a cam. About to go through pump shot jets and cams and maybe a four hole spacer. Keep us posted on what worked and didn't in your journey to throttle response.

I went from a orange pump cam to a blue cam in the primary accelerator pump. Still has a small flutter when I stab the throttle, but only lasts about 3 seconds before the carburetor responds. And it's a big improvement. I just went up in pvcr jets. So hopefully the stumble will be all gone.

 

[68 HEMI GTS]

I went from a orange pump cam to a blue cam in the primary accelerator pump. Still has a small flutter when I stab the throttle, but only lasts about 3 seconds before the carburetor responds. And it's a big improvement. I just went up in pvcr jets. So hopefully the stumble will be all gone.

Usually the stubble is secondary side related if the primary side drives around good. Needs more pump cam or squirter.

Pvcr is to adjust WOT once you have the primary jetting correct for high speed cruise and the secondary jetting is close.

 

[Aron Gleason]

Usually the stubble is secondary side related if the primary side drives around good. Needs more pump cam or squirter.

Pvcr is to adjust WOT once you have the primary jetting correct for high speed cruise and the secondary jetting is close.

Would the orange cam be more aggressive than the white cam?

 

[Aron Gleason]

I was thinking of putting the blue cam in the secondary side but that might be overkill

 

[68 HEMI GTS]

I was thinking of putting the blue cam in the secondary side but that might be overkill

Sounds like its struggling, go for the overkill. There an online chart for those pump cams.

 

[68 HEMI GTS]

 

[Aron Gleason]

Sounds like its struggling, go for the overkill. There an online chart for those pump cams.

After putting the blue cam in the primary, it did make a difference.