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Discussion Starter #1
- 4 bolt main standard piston bore + summit racing flat top pistons
- Summit Racing (sum-1065) Duration 284/284, Lift .458/.458 cam
- Milld-ish ported Vortec heads
- Dual plane intake
- MSD HEI Distributor + "Street Fire" Ignition box
- Advance timing is around 34-35
- Mechanical Fuel pump + Holley Fuel Regulator set a little over 5 PSI
- Brand new Edelbrock 1906 650cfm AVS2 Mech Secondaries

So the problem i am having is that if press the throttle sharply I get a momentary bog or stumble. The engine briefly dies for half a second then picks up. This only happens as soon as i hit the gas.
But if i ease on the throttle slowly i don,t get the bog/stumble. I looked in to the carburetor while i stabbed the gas, and i noticed that as soon as the secondaries open is when i get the stumble. I also noticed that the venturies were pretty slow on flowing fuel out in to the carb when the secondaries open. I did a little test and i sprayed some starting fluid in to the secondaries as soon as they opened and sure enough there was no bog/stumble and it revved strong.

My theory is that the secondaries isn't getting the fuel that is needed from the boosters as soon as the secondaries open, which causes the bog/stumble. If I press the pedal slowly and steadily, the air flap opens slowly, the fuel has time to be pulled to the boosters and the engine picks up. Otherwise, the engine idles smooth and runs smooth besides the stumble.


So my question is, has anyone else ran in to this problem that has a solution? Or does anyone have an idea on what i should do? Would stepping down a metering rod from the stock .070-.032 to a .068-.042 help??

*DISCLAIMER, I AM NOT A CARB TUNING EXPERT*
Things ive tried doing already:
1. Adjusted the air flap on the secondary to be a little tighter on the tension spring than the factory setting.
2. moved the accelerator pump to the notch closes to the carb
3. Sprayed carb clean throughout all the venturies ports and air bleed holes
4. Richened up the secondary jet by going from the stock .098 to a .101
5. Tried every single step up spring
6. Made sure there was no air leaks
7. Advanced the timing a little bit
8. Spark plugs dont look lean or to rich

I am starting to regret purchasing this carb... A friend of mine let me try his 600cfm dual feed holley, and it ran great.
But i don't want to give up so easy on this avs2. Any help/advice would be appreciated! Thanks.
 

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How much did you tighten the air door spring from stock? When we ran an AVS on our Stock Eliminator the door was fairly tight otherwise it would stumble.
 

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I’ve never seen an air valve on any carb open up with a quick stab of the throttle or a steady increase. Or the secondary throttle plate open.
You likely don’t have enough fuel from the accelerator pump combined with not enough timing causing the bog.
 

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Discussion Starter #4
How much did you tighten the air door spring from stock? When we ran an AVS on our Stock Eliminator the door was fairly tight otherwise it would stumble.
I would tighten the screw one full turn and would test it. I did the over and over about 3 or 4 times. So Its pretty tight as of right now, and I still have that bog
 

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Discussion Starter #5
I’ve never seen an air valve on any carb open up with a quick stab of the throttle or a steady increase. Or the secondary throttle plate open.
You likely don’t have enough fuel from the accelerator pump combined with not enough timing causing the bog.
Well when get on the gas and stab it open it bogs as soon as the (mechanical) secondaries open. When I'm on the street and I floor it, it goes, bogs, and then picks up perfectly fine.

I dont have crazy performance parts, so I wouldn't think I would need much more timing ? Would buying the accelerator pump kit from summit help ?
 

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Either the mixture falls lean or the air valve opens too quickly which I'll get into later but first a trip to advance mechanisms.

If you are running a lot of vacuum advance at this point and the rpms are not enough to be picking up much if any centrifugal the act of opening the throttle drops the manifold vacuum and the vacuum advance with it. This will result in a bog that recovers as the rpm staggers upward and the centrifugal comes in. More initial advanve may cure this as would a faster centrifugal may help by bringing more advance in earlier. Here you have to play around to see what's needed. This part of "tuning".

For a mixture falling lean some contributors are suggesting a bigger pump shot to cover the hole. It might, nothing lost in trying it. However, the AVS has an enrichment circuit on the secondary that should turn on momentarily as the air valve exposes it. It could be your engine and drive train combination wants a richer secondary metering, I find it common place to kick the Edelbrock's up one jet size on the secondary side even for pretty mild street engines. For CARB and EPA compliance they are jetting a bit lean out of the box.

Lastly you can sdjust the air valve to slow it down, if your vehicle has high gearing the engine may not be turning fast enough to use all the air the carb offers, this will get a momentary bog till the rpms meet offered supply. There should have been instructrutions on how to do this with the miseable instruction booklet Edelbrock includes. If not there or you have trouble understanding their jibberish come back and I'll try to make sense of it for you, they even wrap my brain around a post with how it's presented.

Bogie
 
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