It is the same system as the Carter AVS, the AVS was an upgrade to the bog prone AFB.
Open the door too fast on an AVS and it will cause a bog.
Dual quads versus big hammer!!!...
- Thread starter j par
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Open the door too fast on an AVS and it will cause a bog.
I call it lean
Exactly. Bog from the door flying open too fast would be lean. J par's been saying bog all along, so we've been saying tighten the door spring. Now its a cough with hesitation. Still could be lean, but if gas is splashing around the top, that's air flow issues to me. The back flaps don't come open and fuel splash under WOT - that is something else.
yellow rose
Overnight Sensation
How can it be lean if the air valve isn't open????? Jpar says the air valves are not opening. Can't be lean without air.
Tomorrow we will know more.
Wouldn't it need "air flow", or vacuum to pull the gas into the secondaries? And if he had that, wouldn't the back flaps be open? If the Demons are like the TQ's, then the back flaps are part of the syphoning process to get the gas into the secondaries. Fact that the rear flaps won't open under WOT is a concern
yellow rose
Overnight Sensation
It is lean on the primary side.
j par
Well-hung Member
You need to write this down on the calendar... From what I'm experiencing I'm agreeing with you... That comment alone should stop the presses LOL...
Everything I do to lean this out seems to make things improve... I'm now leaned the air mixture screws beyond what they should go for their current jetting... I have bigger rods coming tomorrow.. I'm trying to call Summit and get a tracking number for the smaller primary Jets coming the from taxes Warehouse...
Choke does exactly that - it chokes the air, doesn't stop fuel flow. You and I both know this. Per say, if you remove the back flap, it will not only be lean at the initial stomp, it will never recover because the flap (at least on the TQ) is part of the syphoning process. Fuel syphoning is what I'm talking about.
j par
Well-hung Member
Like I was saying it was fat all over. Never seeing the number 13 on my af gauge, between 10 11 and 12....
The fact is the engine will only draw the amount of CFM in. How much CFM does jpars 410 pull in.
It's why I posted post 132
j par
Well-hung Member
Not on the road particularly. I've done it in the driveway to see what it did and the other day I tried it Progressive and that's about as close as I got I guess..
j par
Well-hung Member
Hopefully 1250 LOL...
...
The reason I ask is it's demand of CFM's that pulls the back flaps open. You may not be drawing enough to pull both doors open, so both stay shut. IF you run off of just one carb, and it pulls that back flap open in a second, then that answers it.
j par
Well-hung Member
when I disconnect the carburetors and it's idling and warm. I can blip the throttle and it smacks the rear door open on either carburetor. Those primaries are so damn small there's no way those secondaries don't come into demand. I'm not saying all of them but I'm not sure as well... One thing for sure I feel like I'm about halfway there and then feeling I got yesterday from the car finally gave me quite a relief that I was heading in the right direction.. and that direction was much leaner...
j par
Well-hung Member
If I had to take a wild guess at it right now I want to put one step leaner primary Jets, I have a one-step leaner set of secondary Jets I haven't tried yet and put those in, drill 5/16 holes in a couple of secondary doors and see what happens...
PRH
Well-Known Member
I think the basic problem here is the very large change in capacity of these carbs when going from part throttle to wot at low speeds.
The old carbs(which were also air valve secondary) have the 4 barrels not so different in size.
So, the primary side has more capacity, the secondary side isn’t as much of an increase in total capacity when they’re opened.
Imagine if the carbs were staggered Venturi diameters, but reversed from normal.
Big primaries, small secondaries.
Intuitively...... you’d expect that would have no bog issues when engaging the secondaries.
As the size of the secondaries grows in relation to the primary side...... coupled with the carbs overall capacity being way beyond what the motor can effectively use........ getting a smooth, clean activation of the secondaries will become more of a challenge.
This has already been demonstrated in this application.
When the carb linkage is disconnected so one carb can be operated as a single unit, the secondary air door operates properly.
By doing that, you have doubled the air flow through the carb(or halved the capacity..... as the motor sees it......whichever way you want to look at it).
At any given rpm, unless you specifically severely limit the carb capacity, the motor is going to try and ingest the same amount of air through the one carb.... or two of them.
Two carbs don’t flow twice as much into the motor...... they just flow 1/2 as much through each carb than if there were only one carb.
This style of carb is dependant on air flow for proper secondary operation, so cutting the air flow in 1/2, creates a problem/challenge.
As for the jetting leaner for cruise.......
My experience in general is that “jetting” has a pretty noticeable impact at lower throttle settings(even carbs that have big restrictions in the fuel passages and don’t respond to jet changes at high rpm with still be noticeably richer with bigger jets at lower throttle settings).
The area of the jet is larger in proportion to the available air capacity at low throttle settings than at larger throttle settings.
Since there are two carbs, they are open even less than normal for part throttle operation........ and there is reduced air flow.
So, it’s normal to see the jetting be quite rich at part throttle with 2 carbs with jetting thats stock or “normal”.
What you have to watch for is, as the throttle settings get open farther, that there is still enough jet area to match the air flow, and that at higher load part throttle settings(like going down the highway at 3500rpm), that you don’t end up with a lean condition.
It’ll either still be fine, or it won’t.
That’s where the O2 gauge really comes in handy.
The old carbs(which were also air valve secondary) have the 4 barrels not so different in size.
So, the primary side has more capacity, the secondary side isn’t as much of an increase in total capacity when they’re opened.
Imagine if the carbs were staggered Venturi diameters, but reversed from normal.
Big primaries, small secondaries.
Intuitively...... you’d expect that would have no bog issues when engaging the secondaries.
As the size of the secondaries grows in relation to the primary side...... coupled with the carbs overall capacity being way beyond what the motor can effectively use........ getting a smooth, clean activation of the secondaries will become more of a challenge.
This has already been demonstrated in this application.
When the carb linkage is disconnected so one carb can be operated as a single unit, the secondary air door operates properly.
By doing that, you have doubled the air flow through the carb(or halved the capacity..... as the motor sees it......whichever way you want to look at it).
At any given rpm, unless you specifically severely limit the carb capacity, the motor is going to try and ingest the same amount of air through the one carb.... or two of them.
Two carbs don’t flow twice as much into the motor...... they just flow 1/2 as much through each carb than if there were only one carb.
This style of carb is dependant on air flow for proper secondary operation, so cutting the air flow in 1/2, creates a problem/challenge.
As for the jetting leaner for cruise.......
My experience in general is that “jetting” has a pretty noticeable impact at lower throttle settings(even carbs that have big restrictions in the fuel passages and don’t respond to jet changes at high rpm with still be noticeably richer with bigger jets at lower throttle settings).
The area of the jet is larger in proportion to the available air capacity at low throttle settings than at larger throttle settings.
Since there are two carbs, they are open even less than normal for part throttle operation........ and there is reduced air flow.
So, it’s normal to see the jetting be quite rich at part throttle with 2 carbs with jetting thats stock or “normal”.
What you have to watch for is, as the throttle settings get open farther, that there is still enough jet area to match the air flow, and that at higher load part throttle settings(like going down the highway at 3500rpm), that you don’t end up with a lean condition.
It’ll either still be fine, or it won’t.
That’s where the O2 gauge really comes in handy.
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lean or rich.... ok, that wouldn't be my concern. IF those flaps don't come open, your in trouble. And, as you have discovered, TQ's and the such with a back flap cannot be set in the garage idling in neutral. Trust me, for years TQ's were the carb of my choice and all I ran. Tuning them to 340's, 360s, and even 318's in heavy trucks with tight converters, and no bog. Going lean on the primaries could be "offsetting" for the back flaps not opening. It runs better, but not the solution to your problem. I cannot believe a 625 Demon out of the box that was designed for a stock 350 Camaro is too fat for that 410 C.I. with headers and ported heads. I'm not there, but I think it's deeper than leaning out your primaries.
K.O. SWINGER
Meeting in the alley since 1976
Put down the drill and step back away from the carburetors bro it's just not worth it! You're not thinking rational, come back to the light LOL
j par
Well-hung Member
I have four extra rear air doors for this purpose coming tomorrow.. I'm not going to do like yellow rose suggested and start drilling my original doors LOL I'm going to wait till tomorrow... So I still have to work tomorrow Friday and through the weekend as well. Probably won't be till early next week till we see any more results. But getting ideas to try and grind on is great...
j par
Well-hung Member
Thank you... My O2 gauge again is just seeing Rich everywhere. and now that I got it a little bit leaner it. Only seems to have an improvement and the O2 gauge is starting to see readings that I used to see a little bit more normal with the Edelbrocks.. and also thank you again for those articles or post from other forms that you found earlier. Very interesting reading.. I haven't been able to find anything really on this dual set up. But some of those were saying extra horsepower and that was encouraging...
Of course all that was 6 to 8 years ago...
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