Another Holley 3810 question
11-18-2018, 07:52 AM
#41
Race Director
Well, there you go tbarb, giving me more stuff to adjust.
I had not noticed the rear blades are offset mounted - it must not be much. I didn't measure exactly but my secondary's are cleared by the link to start opening at probably 10 to 15 degrees primary throttle movement. I'll see what I have at around 45 degrees movement. I did check at full throttle to make sure the secondary's were able to open 100%.
I had not noticed the rear blades are offset mounted - it must not be much. I didn't measure exactly but my secondary's are cleared by the link to start opening at probably 10 to 15 degrees primary throttle movement. I'll see what I have at around 45 degrees movement. I did check at full throttle to make sure the secondary's were able to open 100%.
Last edited by DansYellow66; 11-18-2018 at 07:54 AM.
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steve meltzer (11-18-2018)
11-18-2018, 09:28 AM
#42
learnin' all the time. thanx guys. much appreciated. s
11-18-2018, 10:56 AM
#43
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From my research I just want to add to the information about the secondary closing link.
I always thought the same as Dan about the link holding the secondary blades closed at idle but that's not it's purpose. When lifting the throttle the link will mechanically close the secondary blade but the air above at atmospheric pressure will force them closed at idle because the blade area is offset.
The secondary link is adjusted correctly when at 1/3 to 1/2 primary throttle blade opening the link allows the secondary blades to be open approx the same amount as the primary blades. At this point, both the primary and secondary blades will continue to open the same amount all the way to WOT. When adjusted like this there will be some play in the link at idle, remember the air against the offset blade keeps the secondary blades closed at idle.
This will ensure that when the secondary blades open they are held against the link and open equally with the primary blades, that is the desired effect when the secondary is tuned correctly.
I always thought the same as Dan about the link holding the secondary blades closed at idle but that's not it's purpose. When lifting the throttle the link will mechanically close the secondary blade but the air above at atmospheric pressure will force them closed at idle because the blade area is offset.
The secondary link is adjusted correctly when at 1/3 to 1/2 primary throttle blade opening the link allows the secondary blades to be open approx the same amount as the primary blades. At this point, both the primary and secondary blades will continue to open the same amount all the way to WOT. When adjusted like this there will be some play in the link at idle, remember the air against the offset blade keeps the secondary blades closed at idle.
This will ensure that when the secondary blades open they are held against the link and open equally with the primary blades, that is the desired effect when the secondary is tuned correctly.
Steve, if you still have the carb off the engine, check the secondary idle adjustment screw (it is on the opposite side of the carb from the throttle arm and is only visible when you turn the carb upside down). It should be adjusted just slightly so the transfer slot looks like a square when viewed from the bottom. This ensures a small amount of fuel is drawn through the secondary idle circuit. If the secondaries stay closed for a long period of time, the secondaries can gum up. You have probably noticed that no matter how high you rev the engine while the car is parked, the secondaries never open. Without a load on the engine, the secondaries will never open. Sometimes the combination of infrequent driving, insufficient engine loading, and new gas blends can conspire to gum up secondaries that are rarely used.
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steve meltzer (11-18-2018)
11-18-2018, 02:36 PM
#44
Factoid: " A vacuum secondary will not open at all until the vacuum is sufficiently high enough for it to overcome the spring pressure in the canister, pulling the secondary blades open, but only to the point ALLOWED by the linkage bar Steve referenced."
I've never understood this, so now's a good time for me show my ignorance. Engine vacuum is at it's max value at idle, right? So wouldn't vacuum secondaries open with a FALLl in vacuum, not a rise, like at WOT?
Also, since i've got all of you smart guys helpin' me (thanx so much!)...The carb is leaking fuel from the passenger side and, it doesn't seem to be either bowl nor the accelerator pump. What and where do I look next?
thanx for the schoolin' and education. much appreciated.
steve
I've never understood this, so now's a good time for me show my ignorance. Engine vacuum is at it's max value at idle, right? So wouldn't vacuum secondaries open with a FALLl in vacuum, not a rise, like at WOT?
Also, since i've got all of you smart guys helpin' me (thanx so much!)...The carb is leaking fuel from the passenger side and, it doesn't seem to be either bowl nor the accelerator pump. What and where do I look next?
thanx for the schoolin' and education. much appreciated.
steve
Last edited by steve meltzer; 11-18-2018 at 02:37 PM.
11-18-2018, 02:45 PM
#45
tbarb, that sounds like the description of a mechanical secondary, not a vacuum secondary carb. A vacuum secondary will not open at all until the vacuum is sufficiently high enough for it to overcome the spring pressure in the canister, pulling the secondary blades open, but only to the point ALLOWED by the linkage bar Steve referenced.
Steve, if you still have the carb off the engine, check the secondary idle adjustment screw (it is on the opposite side of the carb from the throttle arm and is only visible when you turn the carb upside down). It should be adjusted just slightly so the transfer slot looks like a square when viewed from the bottom. This ensures a small amount of fuel is drawn through the secondary idle circuit. If the secondaries stay closed for a long period of time, the secondaries can gum up. You have probably noticed that no matter how high you rev the engine while the car is parked, the secondaries never open. Without a load on the engine, the secondaries will never open. Sometimes the combination of infrequent driving, insufficient engine loading, and new gas blends can conspire to gum up secondaries that are rarely used.
The closed throttle blade adjustment for the vacuum secondary is approx 1/4 turn on the stop screw, just enough so the blades don't stick in there bores because the vacuum servo will not be strong enough to snap them open so you want the screw just holding them from completely stuck shut.
If you adjust the secondary blades into the transfer slot the car will run very rich, usually the slot is higher on the vacuum secondary carburetor. Also, the secondary idle air bleed is very small on the vacuum carburetor so when the blades open the mixture is rich to avoid a lean condition created because there is no accelerator pump shot.
On some vacuum secondary Holley's there are tiny constant feed discharge holes (approx .020) in the secondary below the transfer slot which serve just the purpose of a small fuel draw and that keeps the fuel from getting stale in the back bowl if you drive like gramma, I'm sure none of us need to worry about that. :-)
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Factoid (11-18-2018)
11-18-2018, 02:56 PM
#46
Factoid: " A vacuum secondary will not open at all until the vacuum is sufficiently high enough for it to overcome the spring pressure in the canister, pulling the secondary blades open, but only to the point ALLOWED by the linkage bar Steve referenced."
I've never understood this, so now's a good time for me show my ignorance. Engine vacuum is at it's max value at idle, right? So wouldn't vacuum secondaries open with a FALLl in vacuum, not a rise, like at WOT?
Also, since i've got all of you smart guys helpin' me (thanx so much!)...The carb is leaking fuel from the passenger side and, it doesn't seem to be either bowl nor the accelerator pump. What and where do I look next?
thanx for the schoolin' and education. much appreciated.
steve
I've never understood this, so now's a good time for me show my ignorance. Engine vacuum is at it's max value at idle, right? So wouldn't vacuum secondaries open with a FALLl in vacuum, not a rise, like at WOT?
Also, since i've got all of you smart guys helpin' me (thanx so much!)...The carb is leaking fuel from the passenger side and, it doesn't seem to be either bowl nor the accelerator pump. What and where do I look next?
thanx for the schoolin' and education. much appreciated.
steve
There are two different types of vacuum created in the engine. Manifold vacuum which is created by the pistons going up/down which is what you are referring to and venturi vacuum that's created when the throttle blades are opened and the air that rushes into the venturi creates a low pressure (vacuum) in the reduced area of the venturi. That is where your secondary vacuum servo gets it's signal.
Search for a post a few days ago where I explained it better.
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steve meltzer (11-18-2018)
11-18-2018, 04:50 PM
#47
As I was typing my previous reply, i was thinking that maybe it was Venturi vacuum about which you were speaking, not manifold vacuum. I got it now. I assume that having that very small "square" opening in the transfer slot of the secondaries is still correct. The tech at Holley agreed with that setting. s
11-18-2018, 05:50 PM
#48
Race Director
I tried checking my secondary opening with the primary's at 50% open - tough to do accurately on the car. It looks like my secondary's are allowed to open a bit less than 50% at that point - but they are allowed to open fully at full throttle. I will probably pull the carb after a few more drives to re-tighten all the base plate screws again and I'll check it a little closer then.
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steve meltzer (11-20-2018)
11-19-2018, 06:23 AM
#49
As I was typing my previous reply, i was thinking that maybe it was Venturi vacuum about which you were speaking, not manifold vacuum. I got it now. I assume that having that very small "square" opening in the transfer slot of the secondaries is still correct. The tech at Holley agreed with that setting. s
If the carburetor is a four corner idle carburetor ( idle adjustment screws on all corners) then the transfer slot is cut lower in the throttle body and needs to be active. The four corner carburetors have idle circuit calibrations similar to the primary side (IFR-IAB) so they don't run rich.
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steve meltzer (11-20-2018)
11-19-2018, 02:13 PM
#50
Thanx tBarb, So, on my 3810 the secondary plate should not show any of the transfer slot, right? thanx again. s
11-19-2018, 02:54 PM
#51
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Steve, I agree with tbarb on the correct adjustment for the secondary idle adjustment on your carb. The Holley tech and I were both referring to a carb with four corner idle mixture adjustments which your carb does not have.
Last edited by Factoid; 11-19-2018 at 02:57 PM.
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steve meltzer (11-20-2018)
11-19-2018, 04:31 PM
#52
Race Director
I would be careful of the information you get from the Holley techs. I called them up a few years ago to discuss primary and secondary float settings on Holley 1850s that are reverse mounted on my ERA Cobra per factory Ford dual quad intake. They didn't understand the question at all. s
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steve meltzer (11-20-2018)
11-20-2018, 09:43 PM
#53
took the PS pump out of the car, as it was failing, then promptly went on vacation! So, it'll be a bit before i get back on this. thanx again guys, for all of your help. s