Help me get the off-idle stumble out of my QF 750-AN Double Pumper

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goldduster318 said:
The intake is an Edelbrock Performer RPM Air Gap

No nitrous or Edelbrocks...from my experience you're more likely to get an off idle stumble with an edelbrock than a Holley type carb regardless.
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My experience was the opposite. Tinkered with a 750 Street Avenger untill i was blue in the face.Put an Ede on and burned rubber all the way down the street. Either way,I was just funning.
I'm sure it's an easy fix,just got to find it.
Wish you luck.
 
I'd find the point the starter kicks back, retard 2* and start there for initial. It may help clear up a lot of idle/off idle issues. You'll have to monkey with the distributor advance which isn't hard.
 
Ok, so without changing anything else, I put the 0.033" idle feed restrictors in the primary metering block only. This did basically remove the off-idle stumble, which makes the car a lot easier to drive.

It did, however, make the cruise in the 1200-2000 rpm range pig rich (11.5-12.3 AFR) I just wanted to see what would happen, so I went back down from 65 air bleeds to 71's. This is just on the edge of the stumbling coming back. The cruise air-fuel leaned slightly to 12.0-12.8.

I think the next step will be to put in the 0.032 idle feed restrictors (I bought 0.032, 0.033, 0.034) and see what that gets me.

I had actually tried bumping the timing long before, and strangely I had almost 40 degrees in it at idle and it would still start without drama. It didn't do much for this issue, though....but that was before I put the fuel pressure regulator on.
 
put the .032 idle feed restrictors on both metering blocks, and then try the .070 idle air bleed. are you at sea level? or above sea level? whats your elevation?
 
Well guys, the stumble is basically gone with this setup:

0.032 idle feed restrictors in the front metering block
65 air bleeds in front and 71s in rear
35 primary squirter.

Timing 22 up front and 35 total.

It does cruise a little rich so I might stick some larger air bleeds back in to help with that a bit.

In SE MI, we are between 620 and 700 ft above sea level.
 
goldduster318 said:
Hello all,

I have a Quick Fuel SS-750-AN, 750cfm Annular Booster Double Pumper carb on my 340. This carb seems to run great in all areas except right off of idle and if you get into the throttle a little bit at low RPM in 4th gear.

The car is a '70 Duster, full weight, 4-speed, and 3.23 gear.

Primary Jet: 68
Secondary Jet: 78
Idle Air Bleed: 69/69
High Speed Air Bleed: 29/29
Primary Squirter: 31
Secondary Squirter: 31
Power Valve: 8.5

Fuel Pressure is 6 psi with a regulator and the fuel level in the bowls is just slightly below the center of the window.

I have a wideband on it, and I'm satisfied with the A/F at any rpm above 2300, below that it seems to go lean/rich a bit depending on RPM/load

At idle, the A/F ratio is between 13.5 and 14:1 (950rpm)
When I pop the clutch, the engine stumbles and leans out on the wideband into the 16-17:1 range for a second then recovers. In many cases it becomes a bit rich after this.

Any ideas on how to get rid of this stumble? I've tried several accellerator pump cams and haven't really gotten rid of it. It seems to be best with either the brown or green pump cam.

Thanks for any help!
Click to expand...
 
goldduster318 said:
Hello all,

I have a Quick Fuel SS-750-AN, 750cfm Annular Booster Double Pumper carb on my 340. This carb seems to run great in all areas except right off of idle and if you get into the throttle a little bit at low RPM in 4th gear.

The car is a '70 Duster, full weight, 4-speed, and 3.23 gear.

Primary Jet: 68
Secondary Jet: 78
Idle Air Bleed: 69/69
High Speed Air Bleed: 29/29
Primary Squirter: 31
Secondary Squirter: 31
Power Valve: 8.5

Fuel Pressure is 6 psi with a regulator and the fuel level in the bowls is just slightly below the center of the window.

I have a wideband on it, and I'm satisfied with the A/F at any rpm above 2300, below that it seems to go lean/rich a bit depending on RPM/load

At idle, the A/F ratio is between 13.5 and 14:1 (950rpm)
When I pop the clutch, the engine stumbles and leans out on the wideband into the 16-17:1 range for a second then recovers. In many cases it becomes a bit rich after this.

Any ideas on how to get rid of this stumble? I've tried several accellerator pump cams and haven't really gotten rid of it. It seems to be best with either the brown or green pump cam.

Thanks for any help!
Click to expand...


Sounds good MD it's to lean,I just fixed mine,,,,you need bigger squirter in back ,,31 front,,,try 33,,,35,, I just drilled mine out with,1/16 th bit,,and is slot on now no stumble,,,, make sure pumps are set,,,and you will get it,,,,one thing at a time,,,,I'm sure this will help ya out,,,
 
If it back fiers thru carb or a slight stumble ,it's to lean,,,back fire thru exhaust,, to rich,,,, to fix stumble increase back squirter ,,,,set cam's correctly,,,,change one thing at a time you will fix the issue,,,,,,
 
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