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vic392
AFB jets for 392


Hey group.
I'm running an Edelbrock 1407 750CFM, mechanical secondaries, on the stock 392 intake (machined to fit the throttle plate size). The 392 has 10:1 forged pistons with Bob's solid lifter cam - B777@108 (.480 lift, 240 Dur .050, 108 ls). I'm having trouble getting the jetting right. Finally got the primaries about right using 0.116" jets but can't find the right setup for the secondaries. I have a 96gph fuel pump and put in larger float needles and inlet valves. Runs great and pulls hard until the secondaries open, then just goes flat with no power until I back off to just the primaries again. It feels like a fuel starvation problem but my Innovate O2 sensor reads about 10 which indicates rich. I'm up to 0.116" secondary jets but started with stock which were 0.107" so I keep enriching the A/F mix. The sensor says to leaner but it seems like that's not the way to go since I had to open up the primaries to get their A/F mix anywhere near 14. It started out in the 20's.

In my trials, I disconnected the secondaries so I could dial in the primaries. Once they were close, I hooked the secondaries back up and that's when I'm having the problem. It's not just a momentary bog, It just loses power and won't recover until I back off to just the primaries.

Anybody running anything close? If so, what your jet sizes?
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on: Fri 06 of Dec, 2013 [06:04 UTC] reads: 19362

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billm
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Re: AFB jets for 392
on: Fri 13 of Dec, 2013 [16:39 UTC] score: 0.00
Hi Vic,

I listed a response on the 12th, but I just found something interesting. A friend brought his Edelbrock Performer carburetor to me a few days ago. His symptom was extremely rich running and fouling of the spark plugs within 30 miles or so. I found one of his floats was set too high. He's also running an electric fuel pump of unknown pressure, so I suggested he install a regulator.
Here's the good part. I found evidence of fuel in the wells where the secondary air valve counterweights reside. There should not be any fuel in those wells! Any fuel in those wells will immediately be sucked into the engine when the secondary throttles open. This could be your problem. It could explain all of your symptoms. The engine would go very flat and rich when the secondaries open.
I'm still working on my friend's carburetor, so I don't yet know why this is happening. Too much fuel pressure and too high a float level could contribute to the issue, but the air horn gasket should prevent fuel leaking into the air valve wells. A casting defect could cause the problem, but your carburetor worked properly previously, so this is unlikely. My friend's carburetor shows evidence of fuel in both air valve wells, which also indicates the casting flaw idea is unlikely.
Please check for fuel residue in the air valve counterweight wells. Check your fuel pressure (less than 5 PSI) and your float levels. I recommend going back to the standard fuel inlet needles and seats. The Performer (AFB) carburetors are sensitive to too much fuel pressure, and installing larger needles and seats has only made the situation worse. The air horn gasket on my friend's carburetor seemed to be sealing properly, but a warped or nicked casting could allow fuel into the counterweight wells. See what you find and let all of us on Hot Heads know.
Bill


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vic392
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Re: Re: AFB jets for 392
on: Sun 15 of Dec, 2013 [22:29 UTC] score: 0.00
Hi again Bill,
Just so I don't sound like a dope, I meant no fuel in the wells where the secondary air valve counterweights reside - - not the float wells (duh)!
Vic


> Hi Vic,
>
> I listed a response on the 12th, but I just found something interesting. A friend brought his Edelbrock Performer carburetor to me a few days ago. His symptom was extremely rich running and fouling of the spark plugs within 30 miles or so. I found one of his floats was set too high. He's also running an electric fuel pump of unknown pressure, so I suggested he install a regulator.
> Here's the good part. I found evidence of fuel in the wells where the secondary air valve counterweights reside. There should not be any fuel in those wells! Any fuel in those wells will immediately be sucked into the engine when the secondary throttles open. This could be your problem. It could explain all of your symptoms. The engine would go very flat and rich when the secondaries open.
> I'm still working on my friend's carburetor, so I don't yet know why this is happening. Too much fuel pressure and too high a float level could contribute to the issue, but the air horn gasket should prevent fuel leaking into the air valve wells. A casting defect could cause the problem, but your carburetor worked properly previously, so this is unlikely. My friend's carburetor shows evidence of fuel in both air valve wells, which also indicates the casting flaw idea is unlikely.
> Please check for fuel residue in the air valve counterweight wells. Check your fuel pressure (less than 5 PSI) and your float levels. I recommend going back to the standard fuel inlet needles and seats. The Performer (AFB) carburetors are sensitive to too much fuel pressure, and installing larger needles and seats has only made the situation worse. The air horn gasket on my friend's carburetor seemed to be sealing properly, but a warped or nicked casting could allow fuel into the counterweight wells. See what you find and let all of us on Hot Heads know.
> Bill
>

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billm
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Re: Re: Re: AFB jets for 392
on: Mon 16 of Dec, 2013 [16:00 UTC] score: 0.00
Hi Vic,
I hate to admit it, but I'm stumped! It sure sounds like your problem is carburetor related, but you've addressed just about every carburetor issue. Ignition and timing issues wouldn't cause the symptoms you mention. Your cam is pretty wild, but also shouldn't have anything to do with the symptoms.
The only other thing I can think of is if there is a problem with the secondary venturi assemblies, their installation, or fuel not getting to the secondary venturi wells.
At this point, try to borrow a known-good carburetor from someone. Doing so will quickly determine whether you have a carburetor problem- or not. If you don't know anyone locally, I can send you a carburetor to try, but you'll have to pay shipping both ways. If you're interested in this, please respond, and we can contact each other privately.

Bill

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33Willys
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Re: AFB jets for 392
on: Mon 09 of Dec, 2013 [01:42 UTC] score: 0.00
You are running it up to 3000 RPM, floor it, and it goes flat. I am thinking you could have a possible lean issue. May need a bigger shot of fuel. Edelbrock has larger squirters.

HOWEVER: You have a fair amount of duration and that cam will like a fair amount of initial timing. I would shoot for more initial (around 18-20 at least) with a total set at 34 with 36 probably being the max.

Again, get your timing straight for the cam and set up before tuning on the carb. Initial timing at 10 is way too low.

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vic392
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Re: Re: AFB jets for 392
on: Sun 15 of Dec, 2013 [22:11 UTC] score: 0.00
Hi 33,
Thanks for your comments.
I just sent a reply to Bill. I'm guessing you're seeing it.

I also feel like its a lean problem but the O2 reading confused me. You said "If your engine falls flat reading the O2 sensor guage will not be accurate" Can you tell me more about this? Is there too much going on under the bog condition for the sensor to read?

I'll try messing with the timing. I had some detonation before I enriched the primaries so I'm leary about too much advance. I'll try it a few degrees at a time.

For my info - bigger cam means more timing - and I'm assuming more fuel to build more power?

Any comments on my ignition? MP distributor, orange box and Blaster II coil with Mopar resistor, Champion RN12YC plugs, Taylor wires. Any thoughts about if this has the power to burn the extra fuel?

Thanks alot. Keep your thoughts coming.
Vic



> You are running it up to 3000 RPM, floor it, and it goes flat. I am thinking you could have a possible lean issue. May need a bigger shot of fuel. Edelbrock has larger squirters.
>
> HOWEVER: You have a fair amount of duration and that cam will like a fair amount of initial timing. I would shoot for more initial (around 18-20 at least) with a total set at 34 with 36 probably being the max.
>
> Again, get your timing straight for the cam and set up before tuning on the carb. Initial timing at 10 is way too low.

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33Willys
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Re: Re: Re: AFB jets for 392
on: Mon 16 of Dec, 2013 [18:43 UTC] score: 0.00
Here is my suggestion (my opinion): Set your timing curve - intial advance at 20 degrees with total at 30. A hemi will most likely not need more than 30 due to the location of the spark plug - unless you have this on a dyno and it tells you otherwise. Start with getting this correct and then move on to the carb. You have enough duration that you may want to try locking the timing at 28-30 to see if there is an approvement.

I cannot stress enough how important it is to have your timing correct before tackling the carb tuning.

Consider a more cfm carb (or go with 2 625 or 650 cfm carbs). You dont have a high lift cam, but the duration is in the range that you need lots of initial timing. The Edelbrock carb will also respond much better to more intital timing.

Make sure the float levels are accurate, and have no more than 5.5psi fuel pressure. (and make sure the needles are not sticky)

I am not a fan of vacuum advance, but if you are using it, make sure it is working correctly for the curve you need. Or elminate it and just use the mechanical advance in the distributor. (MSD makes this very easy, but can also be done with the factory style distributors)

Now on my engine that is blown, it runs great at having the timing locked. I have it locked at 33 degrees, but pulling out 1 degree per pound of boost. So, at 9 pounds of boost, I have a total timing of 24 degrees. I have 2 750cfm Quick Fuel carbs.

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billm
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Re: Re: Re: Re: AFB jets for 392
on: Tue 17 of Dec, 2013 [21:32 UTC] score: 0.00
Hi Vic and 33Willys,

I agree with 33Willys about having the fuel pressure, float levels, and ignition timing set properly before trying to diagnose the problem Vic is having. I think Vic has addressed most of these issues. Vic hasn't mentioned fuel pressure, and really needs to make sure it's 5PSI or less. This is critical, especially with the larger needles and seats he installed. Vic didn't mention any changes to the fuel system after installing the new cam, before which the engine ran well, so I assumed the fuel pressure wasn't too high. I still recommend Vic re-install the original needles and seats. This is one variable he changed, and it would help to go back to his known-good configuration to help eliminate this variable. I believe Vic mentioned that the fuel pressure is steady at full throttle, so fuel supply shouldn't be an issue.
As 33Willys mentioned, Vic needs to have more static advance. 10 degrees is too low, but 18-20 sounds really high. Vic mentioned that his total advance was 33 degrees, which is close enough not to be an issue for the problems described. I would suggest 14 degrees initial, with a total of 30 degrees as a good starting point. But, this has nothing to do with the symptoms Vic mentions. Vic said he revs to 3,000 RPM before flooring the throttle. At 3,000 RPM, the distributor mechanical advance should be "all-in". The initial advance and the mechanical advance curve have nothing to do with his problem. As long as Vic has the proper total advance at 3,000+ RPM, the static and ignition timing curves are not an issue.
No offense to 33Willys, but he must be a drag racer. Locking the distributor advance and deleting vacuum advance are race-only tactics. A street engine needs a mechanical advance system and a vacuum advance system. Race engines operate at idle and full throttle only. Street engines operate somewhere between idle and full throttle most of the time. That's why the ignition vacuum and mechanical advance systems exist. Car manufacturer's would not have added this cost and complexity unless it was required.
That said, if Vic is running vacuum advance, make sure the static timing is set with the vacuum advance disconnected. The vacuum advance hose should be connected to the "ported spark" nipple on the front of the carburetor (the right front-nipple). But, this has nothing to do with the symptoms Vic mentions. The vacuum advance does nothing at wide open throttle.

Bill




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vic392
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Re: Re: Re: Re: Re: AFB jets for 392
on: Mon 23 of Dec, 2013 [02:48 UTC] score: 0.00
Hey Bill and 33Willys,
I found the problem. It is me!
First of all - you guys are great. Thanks for your comments and suggestions.
Here’s the scoop: “cam timing”.
I thought I owe you guys an explanation since I found the problem.
In desperation, I was going to pull the cam and put my old cam back. To my surprise, and dumb-headedness, I had the crank gear set wrong. It is the type that lets you advance, retard or set the timing normal. I wanted normal. I set the crank gear correctly on the normal keway slot – BUT – lined up the wrong mark with the dot on the cam gear. The result was the cam running in extreme advance. I’m surprised it ran at all. Also glad I didn’t have any valve to piston contact – so my valves are fine. I was quite mad at myself but felt relieved that I found the problem. I lined up the dots correctly, put it back together and it runs like a bandit. I went back to the original fuel inlets and jets. From the instant it fired, I knew all was well – EXCEPT – I needed to let you guys know what I did. To make matters worse, I did this once before on a 392 about 15 years ago and told myself I’d never be that dumb again. Oh well, I did say I’m 64? I’ll use that as my excuse.
All your suggestions couldn’t help my “cam timing” problem. Now that great lopey idle has 15 psi vacuum. I’m sitting at 11 degrees initial and 33 degrees total timing.

Thanks again and Merry Christmas.

> Hi Vic and 33Willys,
>
> I agree with 33Willys about having the fuel pressure, float levels, and ignition timing set properly before trying to diagnose the problem Vic is having. I think Vic has addressed most of these issues. Vic hasn't mentioned fuel pressure, and really needs to make sure it's 5PSI or less. This is critical, especially with the larger needles and seats he installed. Vic didn't mention any changes to the fuel system after installing the new cam, before which the engine ran well, so I assumed the fuel pressure wasn't too high. I still recommend Vic re-install the original needles and seats. This is one variable he changed, and it would help to go back to his known-good configuration to help eliminate this variable. I believe Vic mentioned that the fuel pressure is steady at full throttle, so fuel supply shouldn't be an issue.
> As 33Willys mentioned, Vic needs to have more static advance. 10 degrees is too low, but 18-20 sounds really high. Vic mentioned that his total advance was 33 degrees, which is close enough not to be an issue for the problems described. I would suggest 14 degrees initial, with a total of 30 degrees as a good starting point. But, this has nothing to do with the symptoms Vic mentions. Vic said he revs to 3,000 RPM before flooring the throttle. At 3,000 RPM, the distributor mechanical advance should be "all-in". The initial advance and the mechanical advance curve have nothing to do with his problem. As long as Vic has the proper total advance at 3,000+ RPM, the static and ignition timing curves are not an issue.
> No offense to 33Willys, but he must be a drag racer. Locking the distributor advance and deleting vacuum advance are race-only tactics. A street engine needs a mechanical advance system and a vacuum advance system. Race engines operate at idle and full throttle only. Street engines operate somewhere between idle and full throttle most of the time. That's why the ignition vacuum and mechanical advance systems exist. Car manufacturer's would not have added this cost and complexity unless it was required.
> That said, if Vic is running vacuum advance, make sure the static timing is set with the vacuum advance disconnected. The vacuum advance hose should be connected to the "ported spark" nipple on the front of the carburetor (the right front-nipple). But, this has nothing to do with the symptoms Vic mentions. The vacuum advance does nothing at wide open throttle.
>
> Bill
>
>
>

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33Willys
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Re: Re: Re: Re: Re: Re: AFB jets for 392
on: Mon 23 of Dec, 2013 [16:44 UTC] score: 0.00
Always - Always - Always - when installing a cam, degree it. Always.

Also, push your initial timing closer to 20 and max it at 29-30. You will be amazed at the difference.

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vic392
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Re: Re: Re: Re: Re: Re: Re: AFB jets for 392
on: Sat 28 of Dec, 2013 [03:20 UTC] score: 0.00
Noted. I have degreed cams on my other 392 builds but got lazy. My bad. Lesson learned very well!!

I'll mess with the timing - weather permitting. Won't I have to limit the mechanical (centrifugal) advance if I only want 9-10 added to my initial? The MP distributor has around 25 degrees of mechanical (centrifugal) . I've read about welding up the holes in the advance plate but haven't ever tried it. Thoughts???

Also, are your numbers OK for the street?
Thanks


> Always - Always - Always - when installing a cam, degree it. Always.
>
> Also, push your initial timing closer to 20 and max it at 29-30. You will be amazed at the difference.

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33Willys
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Re: Re: Re: Re: Re: Re: Re: Re: AFB jets for 392
on: Mon 30 of Dec, 2013 [00:26 UTC] score: 0.00
MP has a kit you can buy. It comes with springs and degree keys. You need to get your initial timing closer to 20 degrees, but max your total timing at 29-30.

Again, this is what I would do - if you are looking for good performance out of this engine with that cam. You will have a clean idle and good throttle response. Driveability will be great too. An aftermarket intake would also improve all around too.

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vic392
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AFB jets for 392 - now timing talk
on: Thu 02 of Jan, 2014 [16:18 UTC] score: 0.00
> MP has a kit you can buy. It comes with springs and degree keys. You need to get your initial timing closer to 20 degrees, but max your total timing at 29-30.
>
> Again, this is what I would do - if you are looking for good performance out of this engine with that cam. You will have a clean idle and good throttle response. Driveability will be great too. An aftermarket intake would also improve all around too.

Hey 33willys,
Thanks for the info. I have my initial up to 15 and it's much better. I'll try 20 weather permitting and after getting the kit which is made by Mallory 29014 since MP discontinued theirs.

I've been reading alot about timing for bigger cams. Looks like you know what you're talking about!!! I see Bob W. also says around 30 degrees total (on another thread). I'll go with that, but wanted your comments. I always read that BB mopars like around 35 degrees. Are our Hemi's different than RB mopars? Bob W. says Also, what are your thoughts on no vacuum advance at all. I a have a Mallory Unilite 3757901 without vacuum advance. It's been on a shelf for years because I always thought the vacuum was needed, at least for gas mileage which I'm not worried about. Looks like not for all out racing, but what about for street?

I'll be playing with my MP dist. but may go with the Mallory after I get your comments.

What ignition are you running?
Thanks,
Vic

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33Willys
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Re: AFB jets for 392 - now timing talk
on: Thu 02 of Jan, 2014 [20:36 UTC] score: 0.00
Hemi places the plug in the center of the chamber, therefore the flame does not need to travel across the piston, therefore do not need more advance. Also remember, retarted timing equals more heat.

I have not been fond of the Unilite - seen way too many go bad.

Vacuum advance will help with light driving and fuel mileage - but when trying to dial in a short curve in a distributor, it gets a little difficult to get it done. You will need to have mechanical set for advance and then limit the amount of vacuum advance too. I have even modified the GM HEI for a friends BB chevy, eliminated the vacuum advance and set the mechanical for his needs. Runs great and is a mild performance street car.

I am using an MSD billet distributor, with MSD 6BTM box, blaster 2 coil (high vibration). I have my timing locked out at 33 degrees (no advance at all). The BTM pulls timing out under boost. This car is driven - not trailered. Some of my car show trips are over 8 hour drives.

Now, MSD has a little 'flaw' in that they only have bushings that limit to 18% advance. This is too much. But, FBO (foursecondsflat.com) makes a 10 and 14 degree. So for example, if your initial is at 20, you can have the total at 30. Their ignition systems are supose to be very good too, but I have not used them.



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billm
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Re: Re: Re: Re: Re: Re: AFB jets for 392
on: Mon 23 of Dec, 2013 [15:24 UTC] score: 0.00

Hi Vic,

That's great news! Good detective work! What a nice Christmas present to yourself.
I used one of those multi-slot timing chain sets on my last engine build, and it took me a while to get the correct cam timing. Don't feel bad- it's easy to make a mistake.

Merry Christmas,
Bill

> Hey Bill and 33Willys,
> I found the problem. It is me!
> First of all - you guys are great. Thanks for your comments and suggestions.
> Here’s the scoop: “cam timing”.
> I thought I owe you guys an explanation since I found the problem.
> In desperation, I was going to pull the cam and put my old cam back. To my surprise, and dumb-headedness, I had the crank gear set wrong. It is the type that lets you advance, retard or set the timing normal. I wanted normal. I set the crank gear correctly on the normal keway slot – BUT – lined up the wrong mark with the dot on the cam gear. The result was the cam running in extreme advance. I’m surprised it ran at all. Also glad I didn’t have any valve to piston contact – so my valves are fine. I was quite mad at myself but felt relieved that I found the problem. I lined up the dots correctly, put it back together and it runs like a bandit. I went back to the original fuel inlets and jets. From the instant it fired, I knew all was well – EXCEPT – I needed to let you guys know what I did. To make matters worse, I did this once before on a 392 about 15 years ago and told myself I’d never be that dumb again. Oh well, I did say I’m 64? I’ll use that as my excuse.
> All your suggestions couldn’t help my “cam timing” problem. Now that great lopey idle has 15 psi vacuum. I’m sitting at 11 degrees initial and 33 degrees total timing.
>
> Thanks again and Merry Christmas.



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billm
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Re: AFB jets for 392
on: Sun 08 of Dec, 2013 [20:37 UTC] score: 0.00
First of all, the Edelbrock carburetors do not have mechanical secondaries in the same way a Holley does. The Edelbrock Performer and AVS carbs use an air valve to regulate airflow in the secondaries, much like the Rochester Quadrajet. The Performer carbs use a weighted air valve, while the AVS uses a spring loaded air valve. These air valves only open when the engine requires more air. An air valve stuck closed can cause the symptoms you describe. When you open the secondary throttles, a stuck air valve will cause the engine to go rich. The secondary jets and accelerator circuit will flow some fuel, but you won't be able to get the required air. The engine will run rich and "flat" until you close the secondaries. No amount of jet changing will fix this.
I don't think the air valves are stuck open. This would cause a lean flat spot when the secondaries opened, but would go away as RPM picked up.
To check the air valve, remove the air cleaner, then gently push the air valve open with a screwdriver. The valve should move very freely. There should be no drag or friction whatsoever. If there is, pull the top of the carb and find out why.
That's my 2 cents.
Bill


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vic392
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Re: Re: AFB jets for 392
on: Sun 08 of Dec, 2013 [21:00 UTC] score: 0.00
> First of all, the Edelbrock carburetors do not have mechanical secondaries in the same way a Holley does. The Edelbrock Performer and AVS carbs use an air valve to regulate airflow in the secondaries, much like the Rochester Quadrajet. The Performer carbs use a weighted air valve, while the AVS uses a spring loaded air valve. These air valves only open when the engine requires more air. An air valve stuck closed can cause the symptoms you describe. When you open the secondary throttles, a stuck air valve will cause the engine to go rich. The secondary jets and accelerator circuit will flow some fuel, but you won't be able to get the required air. The engine will run rich and "flat" until you close the secondaries. No amount of jet changing will fix this.
> I don't think the air valves are stuck open. This would cause a lean flat spot when the secondaries opened, but would go away as RPM picked up.
> To check the air valve, remove the air cleaner, then gently push the air valve open with a screwdriver. The valve should move very freely. There should be no drag or friction whatsoever. If there is, pull the top of the carb and find out why.
> That's my 2 cents.
> Bill
>

Hey Bill,
The air valve is free. I've been reading about drilling holes to lighten it up for quicker response or adding weight to slow the response down. So far I just removed it all together for a test and the motor acted the same. I then thought I might have to add weights but haven't tried that yet. I just but the valve back in and can see it open when I crack the throttle in the driveway without the air cleaner on.

Since the motor is flat with or without the air valve, it seems like a lean mix, but I got confused since the O2 sensor read rich. 33Willys said "If your engine falls flat reading the O2 sensor guage will not be accurate." so that helps me sort out the lean vs rich problem.

I might add weight to the air valve and see what that does. What do you think?

By the way, I had to go quite a bit richer on the primaries with the new cam to get a decent A/F ratio. Detonation was real bad until I open up the primary jets.
Vic

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billm
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Re: Re: Re: AFB jets for 392
on: Thu 12 of Dec, 2013 [18:34 UTC] score: 0.00
Hi Vic,

Thanks for your feedback. Something is seriously wrong here (duh!). It sure sounds like a carburetor issue, but I'm puzzled by the symptoms. You mentioned that you've been running the same carburetor on this engine before, and the problems occurred after installing a slightly wilder cam. This tells me the carburetor was okay before the cam swap. I can't offer you any more suggestions, but I have a few comments.
The Performer carbs are calibrated for mild engines. The AVS style carbs are intended for performance engines. Your cam is far from mild, and you'd probably be better off with an AVS style carb as a starting point.
The secondary air valve should not open when revving the engine in a static garage setting. The engine should not require enough air to open the air valve unless it's under a load. The air valve may move slightly, but it should not open.
If you removed the air valve, yet the symptoms were the same, you've got a big problem. You should have gotten a massive bog, if not a backfire through the carb, when the secondaries opened.
Don't mess with the air valve weights or do any other modifications to the carburetor. You've got a very basic problem with your engine or carb, but I don't know what it is. Can you borrow a known-good carb from a friend?

Best luck to you,
Bill

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vic392
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Re: Re: Re: Re: AFB jets for 392
on: Sun 15 of Dec, 2013 [21:52 UTC] score: 0.00
Hi Bill,
Thanks for the notes. I'll try and do better at explaining my tests.

My secondary air valve only moved slightly when revving the engine in a static garage setting since I only cracked the throttle to see what was happening. Of course at it revved and the I saw the valve start to open, I let off. Pulling the air valve out was a desperation attempt since before I installed the O2 sensor, I thought I had a rich problem so I went max lean without the air valve - just for a test. Like you said, I did get a massive bog and a backfire through the carb, when the secondaries opened - however this is what the hemi was doing that started me trying to tune the carb.

I have had the carb apart several times and haven't seen any fuel in the float wells like you found in your friend's carb.

I'm baffled since I've been running the hemi and this carb for several years. It seems like the cam is biting me.

By the way, I'm 64 and have been building and running 392's since I was a kid - but this is the biggest cam I've had yet and first solid lifter. I might have to get a milder cam but would sure like to get this setup going.

Also, I like the mechanical secondaries because I run a 4 speed and need the secondaries to open quick at gear changes. I've stayed away from the AVS for this reason.

I'll probably put my baby under wraps for winter but may get another shot or two if I get the weather to cooperate.

I'm still thinking I'm lean like 33Willys suggests but I'll try messing with the timing. I did have some heavy detonation so I'm leary about too much advance. I'll try it a few degrees at a time if weather permits.

Thanks again. Keep your thoughts coming.

Vic


> Hi Vic,
>
> Thanks for your feedback. Something is seriously wrong here (duh!). It sure sounds like a carburetor issue, but I'm puzzled by the symptoms. You mentioned that you've been running the same carburetor on this engine before, and the problems occurred after installing a slightly wilder cam. This tells me the carburetor was okay before the cam swap. I can't offer you any more suggestions, but I have a few comments.
> The Performer carbs are calibrated for mild engines. The AVS style carbs are intended for performance engines. Your cam is far from mild, and you'd probably be better off with an AVS style carb as a starting point.
> The secondary air valve should not open when revving the engine in a static garage setting. The engine should not require enough air to open the air valve unless it's under a load. The air valve may move slightly, but it should not open.
> If you removed the air valve, yet the symptoms were the same, you've got a big problem. You should have gotten a massive bog, if not a backfire through the carb, when the secondaries opened.
> Don't mess with the air valve weights or do any other modifications to the carburetor. You've got a very basic problem with your engine or carb, but I don't know what it is. Can you borrow a known-good carb from a friend?
>
> Best luck to you,
> Bill

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33Willys
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Re: AFB jets for 392
on: Fri 06 of Dec, 2013 [14:11 UTC] score: 0.00
If your engine falls flat reading the O2 sensor guage will not be accurate. What is your intial timing and what is your total timing - also what do you have for a timing curve?

When does it fall flat? If you hit the throttle hard, does it fall flat right away? Does it fall flat eventually?

Need more description to help you out more. But, you need to make sure your timing and curve are set correctly before tuning on the carb.

Also, check the float levels and fuel pressure. You do not need more than 5psi. Much more than that and the pump can start pushing fuel past the seats.

You will also get lots of help from hotrodders.com forum. (not that you may not here either)

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vic392
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Re: Re: AFB jets for 392
on: Sun 08 of Dec, 2013 [20:06 UTC] score: 0.00
> If your engine falls flat reading the O2 sensor guage will not be accurate. What is your intial timing and what is your total timing - also what do you have for a timing curve?
>
> When does it fall flat? If you hit the throttle hard, does it fall flat right away? Does it fall flat eventually?
>
> Need more description to help you out more. But, you need to make sure your timing and curve are set correctly before tuning on the carb.
>
> Also, check the float levels and fuel pressure. You do not need more than 5psi. Much more than that and the pump can start pushing fuel past the seats.
>
> You will also get lots of help from hotrodders.com forum. (not that you may not here either)

Hi Willys,
I'm running a Mopar Performance dist (haven't touched the curve). with the orange box. Initial is around 10 degrees and total around 33 degrees. I've been playing with the timing but can't seem to make a difference.

I start out at moderate throttle - on the primaries - than floor it around 3000RPM. As soon as the secondaries open, it falls flat. I've tried it at higher and lower RPM but it's the same. When I back off to just the primaries, it recovers and pulls fine, just low on power since it's back to just the primaries.

In the driveway - once I disconnected the secondary linkage - if I open the secondaries only, it runs great. So, only primaries it's OK and only secondaries it's OK. Put them together and it falls flat.

It still feels like a fuel starvation problem, but I have a pressure gauge and it holds fine. When I put in the larger inlet/needle sets I set the floats per Carter AFB specs for these inlets 13/32" Height, 15/16" drop.

I'm stumped!! Primaries OK, Secondaries alone OK, Primaries and Secondaries - FLAT.

Forgot to mention that I've had this motor for quite a few years in my 32 Ford Coupe with this carb (stock jets) and the same manifold. It ran great. I recently changed from a milder hydraulic cam (.459 lift, 230 Dur .050, 110 ls) to this Bob's solid lifter cam (.480 lift, 240 Dur .050, 108 ls). Guess I'm lousy when tuning for a big cam.

I'm running Sanderson Block Hugger headers and 2 1/2" Flowmasters.

Keep your thoughts coming.

Thanks


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