Edelbrock 1407 off idle bog
- Thread starter Baker7888
- Start date
As far as timing concerned I wouldn't get hung up on a setting.
If I was at your car I would do the following.
Leave everything hooked up the way it is, loosen the distributor hold down bolt to where it is snug. Hook up vac gauge to manifold vacuum.
Back the curb idle screw until plates are shut, close the choke until about 1/16 drill bit open. And try to start.
If it doesn't start, adjust idle screw to just get it to idle. Adjust idle mixture screws until best vacuum, then drop idle speed to just above where it wants to shut off.
Then move distributor both directions and watch vac gauge to highest vacuum reading, then move distributor clockwise (retard) about 1/8th inch. Adjust idle speed screw to about 750 or so. You have manual trans so maybe set about 850. Open choke up as it warms up. Let engine idle about 5 min to get fully warm. Figuring you should be 185 to 195*F, shut down and let sit about 5 min.
With choke open and not touching gas, try to start. It should snap. If it doesn't then one press on gas peddle to get one pump shot. Try to start and it should start. Lock down distributor bolt and go drive it. Take out to unused road and stab it from dead stop, hope to hear chirp or more. Let off and shift to 2nd and stab it again. Hope to hear nice chirp.
Hopefully no bog and no pinging. At night (nice and dark) pull number one and set on manifold, start it and should see nice blue spark.
If its still not running right or have to keep running by keeping choke partially closed, then have to find why it's not acting right.
If it is back to running right, take a short drive in town stop and go traffic to see how it acts. If ok, then take it on nice highway drive, highway speed for about 3 hours. Take home, let cool and pull plugs, inspect, and change (up or down) heat range if needed.
I guess words can only explain so much…. When you asked if i built the motor, to me that means starting with a bare block. I started with a used stock 10.4:1 EFI LT1, leak down and compression tested it, then regasketed it, carb swap, cam etc. “Bolt ons”. So i havent been “told” anything. Everything suggested in this thread has already been checked and checked and checked again. Unfortunately it takes time for jets and rods to arrive. I tried to keep the thread alive in hopes if getting some carb specific info while waiting on shipping. I understand the logic of starting at Point A, developing a baseline and working through the motions. I have already done this. It’s the carb. The merry go round here is the mystery that surrounds the 1407. Its all across the internet. Lots of contradicting info with no apparent solution.
What I am unclear on is
A. Why is pump shot hitting butterflies
B. Pump shot amount vs duration. Which is better for off idle bog
C. Pump plunger measurement. Lots of scattered info and procedures on this
The carb was used-rebuilt (reman basically)
I did find correct baseline jets and needles installed. Float height and drop was incorrect. Drop by a long shot.
For sake of conversation, I dont think its wise to set timing based on idle. I have 16” of vac at idle with a fairly radical cam (over stock) I think that is pretty good. But let me ask. How much vac do you think I will pick up by retarding the idle? How much power will i leave on the table everywhere else? Are you suggesting to find the compromise? My road test shows at only 5” the car will take off like a rocket. Again, this is when letting out the clutch. Vacuum drop. This is with choke closed off approx. 1/2 way. Everyone says pump shot-pump shot-pump shot, i am not sure if this is helping or hurting. Also, regarding wideband, I have read that, for example, on takeoff situations (like mine) the accelerator pump can make the wideband read momentarily rich, however the carb is operating by design. The data therefore can be misleading. Just my opinion. I hope jets and needles will at least have some effect
A. Why is pump shot hitting butterflies
B. Pump shot amount vs duration. Which is better for off idle bog
C. Pump plunger measurement. Lots of scattered info and procedures on this
The carb was used-rebuilt (reman basically)
I did find correct baseline jets and needles installed. Float height and drop was incorrect. Drop by a long shot.
For sake of conversation, I dont think its wise to set timing based on idle. I have 16” of vac at idle with a fairly radical cam (over stock) I think that is pretty good. But let me ask. How much vac do you think I will pick up by retarding the idle? How much power will i leave on the table everywhere else? Are you suggesting to find the compromise? My road test shows at only 5” the car will take off like a rocket. Again, this is when letting out the clutch. Vacuum drop. This is with choke closed off approx. 1/2 way. Everyone says pump shot-pump shot-pump shot, i am not sure if this is helping or hurting. Also, regarding wideband, I have read that, for example, on takeoff situations (like mine) the accelerator pump can make the wideband read momentarily rich, however the carb is operating by design. The data therefore can be misleading. Just my opinion. I hope jets and needles will at least have some effect
Last edited:
I had an Edelbrock 750 on a mild 289 eons ago and I don't remember it having any bad habits. I did replace it with a shiny new 600 when I got the money, but I really don't recall being overcarbed being a problem in terms of drivability on that one. It was backed by a C6 and installed in a 92 Crown Vic.
Even I would think that a 750 is too much carb on a 283. I’m glad to hear that it was not. I certainly do not think it’s too much on a 350 despite what the calculator says. Lots of 750/350s out there. Despite all the negativity about Edelbrock. I like the top load design and that the gasket is above the fuel line. If i can get this stumble to disappear it will be an excellent carb.
78Delta88, I owe you an apology. Im not out of the woods but you are on to something with the timing. First thing. My throttle blades are already closed. I followed your directions to a Tee, and i got highest vaccuum (then retard 1/8”) at a whopping 26 degrees base! Combined with my mechanical 16, this can’t fly! Vac can remained disconnected and plugged. I went easy on it, and it did not stumble.
I need to be very clear here. The stumble i have been fighting is at a NORMAL takeoff. Not a clutch dump or hard takeoff.
SO. I certainly cant run 26 degrees of base timing. What’s next? I’m all ears.
By the way, my rods showed up. I started off by richening the cruise circuit. Stumble was unaffected. Cruise power was not as good. Back to stock.
No apologies needed, I understand the frustration.
I started replying earlier, but didn't get to post. Anyway, I didn't take anything said as negative or derogatory.
Try the new jets and rods and see how it goes. It could boil down to just CFM change, mainly smaller primaries and stronger vacuum signal.
On the pumper issue any many don't understand this: even the OEM had problems with off idle transition to acceleration to cruising. So the solution was a pump shot. It's sloppy and many times too rich, but it reduces the bog, so they went with that as a solution.
The Edelbrock carb is a Carter AFB (Aluminum Four Barrel) and it was designed back in the sixties and prevalent with Carter, Ford Autolite/Motorcraft and Mopar's Carter Thermoquad. All very similar and all square bore. GM took different route with Rochester and went Spreadbore.
Yet all had same problem of off idle stumble. This is a lean-out condition that happens when the vehicle is stationary or moving under load, but it is needed to get vehicle to accelerate. OEM solution was to give pump shot of gas. It is sloppy, but it works.
Remember physics?? Friction of Rest is greater than Friction of Motion. When in gear cruising and want to accelerate..., usually no stumble. In motion even if you lean out momentarily, the momentum of rotational force keeps you from experiencing this stumble. When you are sitting still you have no forward momentum and then you get the bog (stumble).
From standing stop or even moving, physics is still Thrust over Weight. On an reciprocal machine like a V8, it boils down to rotational torque. Basically you take ton and half and go from zero to max speed in very little time. So somewhere in there is something that is upsetting that process. So the issue is finding the cause and correcting it.
I started replying earlier, but didn't get to post. Anyway, I didn't take anything said as negative or derogatory.
Try the new jets and rods and see how it goes. It could boil down to just CFM change, mainly smaller primaries and stronger vacuum signal.
On the pumper issue any many don't understand this: even the OEM had problems with off idle transition to acceleration to cruising. So the solution was a pump shot. It's sloppy and many times too rich, but it reduces the bog, so they went with that as a solution.
The Edelbrock carb is a Carter AFB (Aluminum Four Barrel) and it was designed back in the sixties and prevalent with Carter, Ford Autolite/Motorcraft and Mopar's Carter Thermoquad. All very similar and all square bore. GM took different route with Rochester and went Spreadbore.
Yet all had same problem of off idle stumble. This is a lean-out condition that happens when the vehicle is stationary or moving under load, but it is needed to get vehicle to accelerate. OEM solution was to give pump shot of gas. It is sloppy, but it works.
Remember physics?? Friction of Rest is greater than Friction of Motion. When in gear cruising and want to accelerate..., usually no stumble. In motion even if you lean out momentarily, the momentum of rotational force keeps you from experiencing this stumble. When you are sitting still you have no forward momentum and then you get the bog (stumble).
From standing stop or even moving, physics is still Thrust over Weight. On an reciprocal machine like a V8, it boils down to rotational torque. Basically you take ton and half and go from zero to max speed in very little time. So somewhere in there is something that is upsetting that process. So the issue is finding the cause and correcting it.
Thanks. Unfortunately I am back at square one. I have been reading about restricting bypass idle air bleed. I suppose it’s worth a shot. The only other thing I can think of, is limit my centrifugal advance even more so i can run like 20 something degrees of base. And continue to use manifold vac for the can. I honestly think Im pretty maxed out. The 1407 has a bad rep. I wonder if it’s time to move on. I’d hate to have the same issues. The carb is great everywhere else.
Similar threads
