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Old 09-11-2009, 08:27 PM
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350 falls on face when floored

Iím hoping somebody has run into this issue before and can help out. A year ago I bought my brother-in-laws 62 impala SS. It has a mid 70ís 350 with a mild cam (very mild I put that in this winter) , Edelbrock EPS intake manifold and a 1406 carb. He explained when I bought it that when the secondaryís open the car basically dies. Get off the gas and vrrrooom off it goes. He attributed it to a bent gas tank pick up that he bent during an attempt to repair the gas gauge. Sounded reasonable, Iíve seen his work before; heís not the best at repairs and is more concerned about fixing it fast as opposed to correctly.
So I figured no big deal, Iíll take care of this over the winter and finish driving it to cruise nights for the rest of the season. The tank is old so Iíll replace the pickup, gas tank, fuel pump and lines. All the items were readily available, inexpensive and fairly easy to replace. Besides all of it was 46 years old, the tank had quite a bit of sediment in it anyway.

So over the winter I replaced the Tank, fuel lines, Installed an Edelbrock pump(around 5psi), fuel filter, spark plugs, spark plug wires ,cap , rotor ,air filter and heads (donít ask lol). Even after that it still dies when the secondaryís open! So I read up that it could be the small fuel float valves in the carb, Edelbrock makes a larger valve for this purpose. I ordered the larger valves, installed them and same problem!..

This occurs when the car is hot/cold cool or hot days, doesnít matter. Nothing seems to affect how it runs. On the primaries it runs fine. Iím about to order a new (rebuilt) Quadrajet to replace it. I have since replaced the edelbrock with a summit street/strip carb. Still same problem.

As long as itís on the primaries it runs fine, open it up and within 2 seconds bam just like it ran out of gas. Let up ,off it goes(when the bowl fills back up).

Oh and the fuel lines are far away from any heat source.
I posted this on another forum , buts rather slow there.

STUMPED!
Any help would be greatly appreciated!
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Old 09-11-2009, 09:18 PM
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have you checked timing and dist. advance.
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Old 09-11-2009, 09:28 PM
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Quote:
Originally Posted by bobyell
Iím hoping somebody has run into this issue before and can help out. A year ago I bought my brother-in-laws 62 impala SS. It has a mid 70ís 350 with a mild cam (very mild I put that in this winter) , Edelbrock EPS intake manifold and a 1406 carb. He explained when I bought it that when the secondaryís open the car basically dies. Get off the gas and vrrrooom off it goes. He attributed it to a bent gas tank pick up that he bent during an attempt to repair the gas gauge. Sounded reasonable, Iíve seen his work before; heís not the best at repairs and is more concerned about fixing it fast as opposed to correctly.
So I figured no big deal, Iíll take care of this over the winter and finish driving it to cruise nights for the rest of the season. The tank is old so Iíll replace the pickup, gas tank, fuel pump and lines. All the items were readily available, inexpensive and fairly easy to replace. Besides all of it was 46 years old, the tank had quite a bit of sediment in it anyway.

So over the winter I replaced the Tank, fuel lines, Installed an Edelbrock pump(around 5psi), fuel filter, spark plugs, spark plug wires ,cap , rotor ,air filter and heads (donít ask lol). Even after that it still dies when the secondaryís open! So I read up that it could be the small fuel float valves in the carb, Edelbrock makes a larger valve for this purpose. I ordered the larger valves, installed them and same problem!..

This occurs when the car is hot/cold cool or hot days, doesnít matter. Nothing seems to affect how it runs. On the primaries it runs fine. Iím about to order a new (rebuilt) Quadrajet to replace it. I have since replaced the edelbrock with a summit street/strip carb. Still same problem.

As long as itís on the primaries it runs fine, open it up and within 2 seconds bam just like it ran out of gas. Let up ,off it goes(when the bowl fills back up).

Oh and the fuel lines are far away from any heat source.
I posted this on another forum , buts rather slow there.

STUMPED!
Any help would be greatly appreciated!
Well, if it does it with both carbs, it tells me that it is probably the fuel supply to the carb. You say you have "about 5psi" of fuel pressure so that leaves me to believe that you are not exactly sure of the pressure. First thing to do is hookup a fuel pressure gauge and verify what the actual pressure is. Your other comment "let up, off it goes (when the bowl fills back up)" also points to a fuel pressure issue.
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Old 09-11-2009, 10:06 PM
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Not meaning to jack , but I have the same issue. I changed distributors from a stock gm unit to a summit brand, then a msd. There is something you have to adjust (advance) in the inside of the vac advance modulator. Could this be what problem is. I know they come somewhat set.. but is this what needs to be done.

Looks like all the newer distributors have this adjustment inside the vac adv. module.
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Old 09-11-2009, 10:07 PM
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Quote:
Originally Posted by S10 Racer
Well, if it does it with both carbs, it tells me that it is probably the fuel supply to the carb. You say you have "about 5psi" of fuel pressure so that leaves me to believe that you are not exactly sure of the pressure. First thing to do is hookup a fuel pressure gauge and verify what the actual pressure is. Your other comment "let up, off it goes (when the bowl fills back up)" also points to a fuel pressure issue.
Agreed! It seems like a fuel pressure problem to me also..
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Old 09-12-2009, 05:57 AM
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heres a good 1 for all on the subject. i have the same exact 1406. on my 350 sbc, it has the secondary bog, on my buddys car that has a 350 olds, it works just fine, no bog. i put a holley 600 with vacuum secondaries on the sbc and my car runs fine, no bog on secondary opening. if i had to guess, its gotta be a sbc trait or something bacause i also have a 500 cfm (1403 elec choke) edelbrock on my inline 6 and have no problems with it.
even i would like to know on why this is. the best ive been able to do to correct this on my sbc, is to add a ton of timing. and of course when doing so, it pings...
so, like others in this thread, whats the deal? something tells me this is more than just fuel related...
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Old 09-12-2009, 06:37 AM
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Quote:
Originally Posted by tnsmith10
heres a good 1 for all on the subject. i have the same exact 1406. on my 350 sbc, it has the secondary bog, on my buddys car that has a 350 olds, it works just fine, no bog. i put a holley 600 with vacuum secondaries on the sbc and my car runs fine, no bog on secondary opening. if i had to guess, its gotta be a sbc trait or something bacause i also have a 500 cfm (1403 elec choke) edelbrock on my inline 6 and have no problems with it.
even i would like to know on why this is. the best ive been able to do to correct this on my sbc, is to add a ton of timing. and of course when doing so, it pings...
so, like others in this thread, whats the deal? something tells me this is more than just fuel related...
If the fuel system has been checked and is good, it could be that the secondary air valves are opening too quick, not enough pump shot or too small a squirter.

Last edited by S10 Racer; 09-12-2009 at 06:43 AM.
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Old 09-12-2009, 11:50 AM
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Quote:
Originally Posted by S10 Racer
If the fuel system has been checked and is good, it could be that the secondary air valves are opening too quick, not enough pump shot or too small a squirter.
what pump shot? theres no secondary accelerator pump or squirters on a edelbrock,just the boosters and the secondary air flap. and the bog is only on secondary opening.
how about the metering rods, and the springs associated with them?
also, ive read here from previous posts that some people have drilled through the counter weights to help correct the secondary bog, but im not real willing to go through with a task with little info when i know the carb performs flawlessly on my buds on olds engine. and except for a very tame cam upgrade, his engine has no performance mods in it that i dont have in my engine.
yes the fuel system is good, i run both my holley and edelbrock @ 5.5-6 lbs (again, no problem out of the holley) and on my buddies olds, had the psi set @ 6.
can anyone explain why adding a bunch of timing would help this (up like around 5* over where you normally set your timing at)?
to me, this is quite a bit since my static timing is set @ 12* and im running HEI and not a msd. much over 14* and it gets hard to start when at operating temp.
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Old 09-12-2009, 04:28 PM
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No I did check the fuel pressure it , but it's been a while. But i agree it still sound and feels like fuel supply. The reason i dumped the edelbroock was I read how the seconaries workd and want to be able to have more control of when they opened. So I installed the summit carb and the adjustment kit too.

I even swapped the HEI out for the stock point style dist. with a pertronix electronic conversion. I did that mostly for the look because I just dont like the HEI look , too big and bulky to me.

Could it be the compression ratio ? Its a smog motor with 7.5 compression ratio.
I have looked at or replaced everything that would make sense, but nothing changes the symptom,period.

Bob
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Old 09-12-2009, 04:49 PM
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Quote:
Originally Posted by bobyell
No I did check the fuel pressure it , but it's been a while. But i agree it still sound and feels like fuel supply. The reason i dumped the edelbroock was I read how the seconaries workd and want to be able to have more control of when they opened. So I installed the summit carb and the adjustment kit too.

I even swapped the HEI out for the stock point style dist. with a pertronix electronic conversion. I did that mostly for the look because I just dont like the HEI look , too big and bulky to me.

Could it be the compression ratio ? Its a smog motor with 7.5 compression ratio.
I have looked at or replaced everything that would make sense, but nothing changes the symptom,period.

Bob
Is the Summit carb a vacuum or mechanical secondary carb? The only other thing I can suggest is to do a vacuum check to see how much vacuum your motor is pulling. It may not be pulling enough vacuum.
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Old 09-12-2009, 04:57 PM
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Its a vacuum secondary unit. I have the opening of the secondaries held off pretty far up in the rpm. 3500 rpm I think. I kept pushing it up with the spring kit, i purchased the quick swap spring kit to make it easier.
I'm not sure about the compresion ratio, I looked up the approximate year of the motor and saw the 7.5 ratio, and these pistons have some big dishes. The heads are 76 cc big valve heads.

Bob
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Old 09-13-2009, 11:49 AM
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Quote:
Originally Posted by bobyell
Its a vacuum secondary unit. I have the opening of the secondaries held off pretty far up in the rpm. 3500 rpm I think. I kept pushing it up with the spring kit, i purchased the quick swap spring kit to make it easier.
I'm not sure about the compresion ratio, I looked up the approximate year of the motor and saw the 7.5 ratio, and these pistons have some big dishes. The heads are 76 cc big valve heads.

Bob
it could be possible to a degree that its compression related, but my engine has flat tops and 64 cc heads running around 9.5:1 here. im wondering if it could be cam or intake related??
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Old 09-13-2009, 05:42 PM
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Thats what I was wondering. Anybody else ? Could it be the compression ratio,? Good blower motor..lol


It had an edelbrock performer RPM intake which was way too much intake for that motor. I swapped it out for an Edelbrock EPS.

Bob
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Old 09-13-2009, 06:59 PM
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I pulled this off Edelbrocks website on the 1406. After reading it, are you both sure you have the vacuum advance plugged into the correct port on the carb since it has a "timed" & "full" vacuum port?

Designed for small-block and small displacement big-block engines, these carbs are recommended only for stock to Performer level applications. They are not recommended for use on RPM or Torker II intake manifolds. Match with an Edelbrock Performer or Performer EPS manifold and other brands of similar design. Calibrated 2% leaner than #1405. Includes both timed and full vacuum ports for ignition advance. Comes with: Metering Jets - Primary .098, Secondary .095; Metering Rods - .075 x .047; Step-Up Spring - yellow (4" Hg).
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Old 09-13-2009, 08:13 PM
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I've tried both ported and direct vacuum and none. Also I no longer have the 1406 installed . i now have a summit street / strip carb (holley clone)

Bob

Last edited by bobyell; 09-13-2009 at 08:20 PM.
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